How Many Chromosomes do Human Have?

The simple answer to how many chromosomes do humans have is that human beings have 23 pairs of chromosomes. It makes a total of 46 chromosomes.

Out of these 23 pairs, 22 pairs are consisting of autosomal chromosomes and the 23rd pair of chromosomes represents the sex chromosomes.

Chromosomes are the basic part of the inheritance and are responsible for the transfer of traits from parents to offspring. X and Y chromosomes are responsible for the determination of the sex of the next generation.

What are chromosomes?

:star: Chromosomes are hereditary units and are composed of genes. Chromosomes are thread-like structures that are present in the nuclei of humans, animals, and plant cells.

:star: Word “Chromosome” is originated from the Greek language. Chrome means color and soma means body. So, the chromosome is collectively meaning “colored body”.

:star: This term was attributed to this hereditary structure because of specific staining of chromosomes when dyes are applied and the fact was observed by some scientists.

:star: While talking about the structural makeup of chromosomes, they are made up of protein and Deoxyribonucleic acid (DNA) molecule.

:star: Unique characteristics that are attributed to each individual are carried as a message hidden in DNA that is transferred from parents to the children.

:star: 23 pairs of chromosomes that make a total of 46 chromosomes are the actual source to carry the genetic information from parents to child through the process of heredity.

:star: Details that are present in the genetic message carried by DNA - that forms chromosomes - are responsible for the unique traits of each individual that are completely different from others.

:star: How many chromosomes are present in the cell of an organism – whether human beings or plants, determine in which sense and to which extent they will be different from each other.

:star: For example, if we consider some species of insects, they may have just one or two chromosomes while some larger animals such as giraffes have 31 pairs of chromosomes making a total of 62.

:star: Similarly, some other animals yet have a varied range of chromosomes. All species, including humans, have a diploid number of chromosomes.

:star: It means that chromosomes are present in form of matching pairs, you can compare them with a pair of socks or gloves that are exactly similar to each other and serve hand in hand to perform their function.

:star: In each pair, one chromosome is inherited from each parent during the process of fertilization. While considering the number of chromosomes in the cells of human beings, each human cell has 23 pairs and a total of 46 chromosomes.

:white_check_mark: Autosomal chromosomes: While elaboration further, among these 23 pairs, 22 pairs are referred to as autosomes as they have nothing to do with the determination of sex of the offspring.

:white_check_mark: Sex chromosomes: One pair of chromosomes that is consisting of X-chromosome and Y-chromosome are known as sex chromosomes and this only pair defines the sex of offspring.

:star: When there is any problem in this pair of chromosomes, it results in sex-linked problems that are transferred from generation to generation, such as hemophilia is such a medical anomaly that expresses itself in generations if present in the parents.

:star: In this XY pair, the X chromosome is donated by a female parent while the Y chromosome comes from the male parent. DNA and proteins are the structural units of chromosomes while a special section of DNA is referred to as a Gene.

:star: Genes are present as gene pairs at the special points that are known as loci. As a whole, all the genetic material is named as genome and genome is the designing material of offspring.

:star: Nowadays, several chromosome-linked diseases are being treated because of deep genetic study. When genetic studies are done for various individuals, it allows the scientists that are studying genetics to find out the genes that are responsible for different medical conditions.

:star: Studying the genetic makeup of human beings, helps scientists to come up with specific treatments for lethal diseases that are specifically targeting that person’s genome. Mostly the disorders that are being treated or are aimed to be treated are genetic disorders such as sickle cell anemia or thalassemia.

:star: Other than these two disorders, there are several disorders that are caused by the problems in genetic sequence, precisely known as “Genetic error”. One such example is diabetes in which the genes that are responsible for insulin synthesis are not properly sequenced and hence it results in Diabetes mellitus.

:star: A better treatment strategy is only designed if you know the disorder and its roots deeply and clearly. That is the reason, scientists and researchers are focusing the genetic study more than before to come out with targeted treatments.

Discovery of chromosomes

:white_flower: How many chromosomes are present in the human body and how are they arranged are the points to be considered for understanding the problems and designing the treatments.

:white_flower: Chromosomes are too small to be seen by the naked eye and hence the scientists who study heredity, look at cells and cell materials in the microscope. The first cell was looked at by microscope in the late 1800s and at that time, cell study was quite a striking discovery.

:white_flower: Initially, there were no details available regarding the structure and function of a cell and the cell particles, however, with the advancement in cellular studies, now almost every detail regarding cells is in knowledge.

:white_flower: Methodology and technology kept on developing and in the 20th century, scientists had a much better understanding of nuclear material consisting of chromosomes.

:white_flower: The chromosomal study gave scientists a much better and clear vision about the relationship between the problems during inheritance and their expression in the generations.

:closed_book: Read Also :point_down:

Do all cells have DNA?
How do you transcribe DNA into mRNA?
What is inheritance and gene expression?

Structure of chromosomes

:white_flower: For a better understanding of chromosomes and genes and their inheritance in generations, the first step is to understand the structure of chromosomes.

:white_flower: If we consider an individual chromosome, it’s too small to be seen with the naked eye. By using a microscope initially and an electron microscope lately, scientists came out with a clear structural study of this inheritance material.

:white_flower: Two major components that form a chromosome are protein and deoxyribonucleic acid – DNA. One DNA molecule is used in the formation of a single chromosome and DNA is present in coiled form around the larger protein – histone protein.


:question: What if DNA is not coiled around protein?

:white_flower: Well, DNA is composed of smaller subunits and one DNA can have a length of 6 feet if it is placed uncoiled. For better fitting in the cell nucleus, DNA is coiled around the protein and hence can be fitted in the nucleus.

:white_flower: While talking about the structure of DNA, it is present as a double helix or like two springs that are coiled around each other. Either side of this twisted helix is consisting of a nucleotide base and a backbone made up of sugar-phosphate.

:white_flower: Four main nucleotide bases that are taking part in the structure of DNA are:

Adenine – abbreviated as A

Guanine – abbreviated as G

Cytosine – abbreviated as C

Thymine – abbreviated as T

:white_flower: The structural assembly of these bases in the helix plays the main role in the formation of a double helix – a characteristic shape of DNA. Bases are assembled in such a way that adenine is bonded with thymine and cytosine is present in front of guanine forming a link in between them.

:white_flower: If there is any problem in the linking of nucleotide bases, such as if A is not forming a linkage with T, or G is not linked with C, there will be a mess during the process of mitosis. Mitosis is the actual process that forms the base of cell division.

:white_flower: During mitosis, DNA that is present in the form of a double helix is uncoiled, and the two uncoiled strands then form new strands complementary to each of them.

Codons: Genetic Codons are the sequence of base pairs that are the basic recipe for the synthesis of proteins. Three base pairs are combined to form a single codon and different amino acids – that are building blocks of proteins – are then formed by the instructions present in form of codons.

:white_flower: For example, amino acid glycine is formed by a codon that has a nucleotide base sequence as GGG, i.e., three guanine bases are making a codon.

:white_flower: The recipe for each protein is present in a gene and the human genome is the basic responsible factor for the synthesis of proteins in the body.

:white_flower: Proteins are then assigned different functions in the body such as keratin protein is taking part in the manufacturing of hair and insulin is being used for controlling blood sugar level.

:white_flower: Almost all the functions that are being carried out in the body are involving the use of proteins. For instance, enzymes, which are the major catalysts in the biochemical reactions taking place in the body are proteins by nature.

:white_flower: Hemoglobin is a major component of blood and antibodies that make the defense system of the body are also proteins. Thus, it can be said that chromosomes – basic hereditary material – are composed of two main constituents.

1. Proteins – known as histones
2. Deoxyribonucleic acid (DNA)

Centromeres and telomeres

:dizzy: While chromosomes are the long DNA molecules that are coiled around the histone protein for the integration of the structure, the chromosome itself has some other parts.

Centromere: If we look at the shape of the chromosome, it has a constricted region in the center or away from the center, and that constricted part is known as the centromere.

:dizzy: No matter it is named as centromere, it’s not present in the center of the chromosome as it can be misunderstood by the name, it can sometimes present at the peripheral region of a chromosome.

:dizzy: Parts of chromosomes that are present on both sides of the centromere are referred to as arms and hence each chromosome has two arms.

Role of centromere: The role of the centromere in the chromosomes is to keep the chromosome in an aligned form as it goes through the complicated steps involved in the cell division.

:dizzy: During mitosis, when the chromosomal copies are being prepared, the centromere is the region that aids in the attachment of each half of replicated chromosomes, which are named as sister chromatids.

Telomeres: At the tips of each arm of the chromosome, the repetitive DNA stretches that are protecting the tips are known as telomeres.

:dizzy: The integrity of chromosomes is necessary for the proper functioning and division of the cell and if this integrity is not maintained, the cell has to suffer a lot.

:dizzy: In several cells, telomeres sometimes start losing their DNA during each cell division, and unfortunately if all the DNA is lost like this, cell replication isn’t possible anymore and it dies.

:dizzy: Especially those cells who are continuously in a phase of division, such as WBCs, have some special type of enzymes that protect them from losing DNA of telomeres during cell division. In absence of these protective enzymes, it would not have been possible for cells to keep dividing.

:dizzy: Although in several anomalies, telomeres are lost but in the case of malignant tumors, they are usually protected and help in fueling the unchecked growth of cells making the disease life-threatening.

Function of chromosomes

:dizzy: The growth and reproduction of an organism aren’t possible if the cells are not constantly dividing to generate the newer cells. When new cells are formed, they replace the older and dying cells of the body.

:dizzy: Yet for the transfer of genetic material from one cell to another, its necessary for genetic material to remain intact. As DNA is present in chromosomes, thus chromosomes are the defining parts of the nucleus that genetic material is intact and being distributed in other cells during cell division.

:dizzy: Although there are checkpoints to keep all the processes in control, yet it happens sometimes that errors in the genetic material or chromosomal division occur resulting in genome-linked disorders.

:question: What happens when an error occurs in chromosomal division or distribution?

:dizzy: If some changes occur by chance in the count and the structure of the chromosome, it results in serious disorders such as leukemia is the perfect example of the chromosome-linked disorder.

:dizzy: If an exact number of chromosomes are not transferred from parents to children, for instance, one or two chromosomal pair is missing, the property that will be defined in the children by those chromosomes isn’t developed.

:dizzy: An example of such kind of chromosomal problem is Down’s syndrome in which offspring receive an additional copy of chromosome number 21. In normal human beings, there are two copies of chromosome 21 are present.

Inheritance of chromosomes

:ballot_box_with_check: Traits are transferred from parents to children via chromosomes. All the genetic material is confined in the genes and during the process of reproduction, each parent donates a copy of chromosomes so that offspring is having the traits from both of them.

:ballot_box_with_check: Then there is a function of dominant and recessive genes that defines further that trait of which parent will be exhibited and which parent will be suppressed in the children.

Mitosis: Mitosis is the process that controls the division of somatic cells while producing the diploid cells (2n).

Meiosis: Meiosis is also the process of cell division but is present only in gamete cells producing the four haploid gametes.

:ballot_box_with_check: Here is interesting information that only the female gamete cells keep their mitochondria intact while sperm cells of males don’t do this. Thus, the mitochondrial DNA of offspring is only donated by the female parent and not the male.

How many genes are present in the human genome?

:ballot_box_with_check: The human genome is a full set of DNA and the DNA is the hereditary unit that contains all the genetic instructions required for the development of properties of an individual.

:ballot_box_with_check: DNA is a double-stranded helix in which each strand is composed of four types of nucleotide bases. These bases are Adenine, guanine, cytosine, and thymine.

:ballot_box_with_check: Adenine is present opposite to the thymine and is linked with it while guanine and cytosine are paired together. DNA double helix remains its structure intact with the help of a phosphate bridge that acts as a backbone.

:ballot_box_with_check: When collectively considered, the human genome contains about3 a billion of these nucleotide base pairs. All these base pairs are confined in just 23 pairs of chromosomes and that is the miracle of nature.

:ballot_box_with_check: A single chromosome is containing thousands of genes, and all the instructions for the synthesis of proteins are present in these genes. approximately 30,000 genes present in the human genome make about 3 proteins.

:closed_book: See also

Evolution, a theory or fact?
Where does transcription occur and where does translation occur?
What are the steps of lytic cycle?

Number of chromosomes in prokaryotes and eukaryotes

How many chromosomes are present in human or other cells either prokaryotes or eukaryotes? Human beings have diploid chromosomes that mean each cell is having 23 pairs of chromosomes making a total of 46.

:star: While human beings have diploid chromosomes, some species of plants may have hexaploidy chromosomes it means they have 6 copies of 7 different chromosomes and it makes a total of 42 chromosomes.

:star: Generally, all the members belonging to a particular eukaryotic species possess the same number of chromosomes in their nuclei. While chromosomes that are present in mitochondria or plasmid-like smaller chromosomes can be varied in number. This kind of chromosome may be present in multiple copies in each cell.

:star: All those species that make their offsprings by sexual reproduction have somatic body cells that are diploid [2n], i.e., they have chromosomes in pairs. For example, human beings have 23 pairs that make a total of 46.

:star: When reproduction occurs, children get one pair from each parent thus making their total of 46. While gamete cells are haploid because two gametes are combined during the process of sexual reproduction and these haploid chromosomes are produced during the process of meiosis of a normal diploid germ line cell.

:star: When meiosis occurs, smaller parts between the chromosomes of female and male parents are exchanged to create the new chromosome.

:star: Thus, children are getting the traits from both parents, and the property of which parent is dominant is represented in the children while masking the other one.

:star: Haploid chromosomes from each gamete cell when combined in the form of a zygote, the diploid organism is created. Even some species of both plants and animals that are polyploid means such species are having more than two sets of chromosomes.

:star: Mostly tobacco and wheat plants, which are important agricultural plants are polyploid although their ancestors were not like this.

:star: For example, pasta and bread wheat are having tetraploid and hexaploidy chromosomes while opposite to them, wild wheat has diploid chromosomes. Thus, variations are present in the different species.

How many chromosomes are in a human gamete?

:star: Well, that is an interesting fact that although all the other cells present in the human body are having 23 “pairs” of chromosomes, human gamete cells are exceptional in this regard.

:star: Gamete cells have just 23 chromosomes that make them haploid cells. The total number of chromosomes that are present in a single set is represented by n that is a symbol of haploid.

:star: While 2n shows the two sets of chromosomes and so on. For instance, somatic cells have 2n while gamete cells in human beings are having the n number of chromosomes.

:star: The reason for this exception is, when male and female gamete is combined during the process of fertilization, they form a zygote with 46 chromosomes. If there are already 46 chromosomes in gamete cells, the zygote will be having a total of double these numbers.

:star: Haploid gametes are the result of meiosis, a division process that generates the cells each with half number of chromosomes as the parent cell. However, some species may have a part of their life cycle as haploid and the other half as diploid, such as algae.

:star: While some other organisms, for example, ants may live as haploid species throughout their life.

How many chromosomes do Down syndrome have?

:white_check_mark: There are some inheritance or chromosome-related disorders that occur because of some irregularities in the number of chromosomes or structural issues. A similar type of disorder is Down’s syndrome.

:white_check_mark: Normally, when a baby is born, he is having 46 chromosomes in each cell. But a baby with Down’s syndrome has an additional copy of chromosome 21 that is an abnormality. This expression of an extra copy of the chromosome is known as trisomy in medical terms.

:white_check_mark: As trisomy is occurring in chromosome 21, it is also narrated as Trisomy 21, i.e., an extra copy of chromosome number 21.

:white_check_mark: This additional and undesired copy of chromosome 21 results in the abnormal development of both the brain and the body of the baby. This abnormal development causes both kinds of problems including mental and physical.

:white_check_mark: Although there are similarities in the appearances of all the people having Down’s syndrome, yet there are differences in the abilities that they have.

:white_check_mark: The main difference between people with Down’s syndrome from the normal human beings is that they have low IQ levels and speech problems.

Role of chromosomes in Down’s syndrome

Down’s syndrome has three variants according to the problem in chromosome 21 although all these types are too similar to be differentiated by symptoms and characteristics. These types can be defined as:

1. Trisomy 21

This is the most common type of Down’s syndrome and about 95% of people with Down syndrome are having this type. In trisomy 21, each cell of the body is having an additional copy of chromosome 21 hence 3 copies of this chromosome are present in all the cells that are represented by the name.

2. Translocation Down’s syndrome

A smaller number of people are having translocation Down’s syndrome and it is present in almost 3% of people. When there is an extra part or a full extra chromosome 21 is present in the cells but it’s not present as a separate 21 chromosome.

It is translocated to a different chromosome and hence named as translocation Down’s syndrome.

3. Mosaic Down syndrome:

Although present rarely – in up to 2% of people – mosaic Down syndrome is characterized by having regular two copies of chromosome 21 in some cells and an extra coping in others. Thus, it’s a mixture of normal and abnormal chromosome 21 and hence named mosaic Down’s syndrome.

Those people who are suffering from mosaic Down syndrome have some characteristics or features in common with other types of Down’s syndrome while differentiating in some because of cells with normal copies of chromosome 21.

Frequently asked questions

Several questions are relevant to how many chromosomes in humans. Some of them have been answered in this section briefly yet precisely.

1. What are 24 chromosomes?

  1. Although it sounds weird that human beings have 24 chromosomes. But it doesn’t mean that human beings are having 24 pairs of chromosomes making 48 chromosomes in total.

  2. It’s about the type of chromosomes that human beings have. Human beings – known as Homo sapiens – have 24 chromosomes in the sense that 22 chromosomes are autosomal, one is -chromosome and the 24th is Y-chromosome. Both X and Y chromosomes are sex chromosomes.

2. How many sexes do humans have?

  1. Human beings normally have 2 sexes that are male and female. Sometimes, due to chromosomal errors, there may be a third type of sex in human beings that is called transgender.

  2. However, based on reproductive cells and sexual reproduction, females are characterized by ovules while males are characterized by having spermatocytes.

3. Do humans have 48 chromosomes?

  1. Normally, human beings have 46 chromosomes that are present in form of 23 chromosomal pairs. Out of these 23 pairs, 22 pairs of chromosomes are autosomal while the last pair is consisting of sex chromosomes.

  2. However, if they’re a human being is having 48 chromosomes, it means it’s not a normal condition. Chromosomal aberration may result in such manipulations that express themselves in form of some chromosome-linked disorder.

4. What gender is the XXY chromosome?

Klinefelter syndrome!

  1. While observing the chromosomal makeup of a normal human being, it’s obvious that a female offspring has two X chromosomes and a male offspring has one X and one Y chromosome.

  2. In some conditions, the child is having XXY chromosomes which means he is carrying an extra chromosome. This disease is known as Klinefelter syndrome and although the child is having male gender yet female characteristics such as enlarged breasts are apparent in such a child.

5. Can females have XXY syndrome?

No!

  1. The presence of a Y-chromosome in the set shows that the child will be male. Normal males have XY chromosomes while the X chromosome is donated by the female parent and the Y chromosome comes from the male parent.

  2. But, if a child has XXY chromosomes, it means although he is male, yet he will be having some characteristics that are attributed to females. However, a female can’t have XXY syndrome.

Conclusion

  • The simplest answer to the question that how many chromosomes do humans have is that human beings have 23 pairs of chromosomes.

  • Having 23 pairs of chromosomes makes a total of 46 chromosomes and out of these 23 pairs, 22 pairs are consisting of autosomal chromosomes while the last or 23rd pair represents the sex chromosomes.

  • Chromosomes are the basic part of the inheritance and are responsible for the transfer of traits from parents to offspring. X and Y chromosomes are responsible for the determination of the sex of the next generation.

  • Chromosomes are made up of deoxyribonucleic acid (DNA) and DNA threads are coiled around large histone proteins. DNA is consisting of genes and all the details about heredity characters are present in the genetic message.

  • Mitosis and meiosis are the processes that are involved in the cell division and development of new organisms. Mitosis produces cells with diploid chromosomes that are copies of parent cells.

  • Meiosis is the process of cell division that is present in genetic cells and it results in four haploid copies of chromosomes. Thus, haploids from both parents when combined result in a new diploid set of chromosomes.

  • If there is any irregularity in the number or structure of chromosomes, it is expressed in form of some chromosomal-linked syndromes such as Klinefelter syndrome in which XXY chromosomes present in the male represent themselves in form of some female characteristics.

Autosome chromosomes are responsible for storing the genetic material that is common to that species, including the similarities between males and females. On the other hand, there is another type of chromosome responsible for sexual differences. Stay with us to know everything about autosome chromosomes!


Chromosomes are spiral chromatin filaments, present in the nucleus of all cells.

Chromatin is formed by DNA molecules associated with proteins of two classes, histones and non-histone chromosomes.

Chromatin can be presented in the form of euchromatin or heterochromatin:

  • Euchromatin: Consists of active DNA that can perform transcription.
  • Heterochromatin : Consists of very condensed, inactive DNA that cannot transcribe genes.

What are chromosomes?

It is known that all species have genetic material, that is, a sequence of molecules that encode what each individual will be like. The union of two individuals results in a new being, which bears some similarities to each of its parents.

In biology, in the field of genetics, this is what we mean when we talk about chromosomes. Each strand of DNA in your body will intertwine with each other until it forms a chromosome, a small piece of the cell that will be passed on to the next generation in reproduction.

There are haploid individuals (N - each 1 chromosome corresponds to a characteristic that forms the being) and diploids (2N - each pair of chromosomes corresponds to a characteristic that forms the being).

The human species is diploid, that is, it has a number of chromosomes as follows: 2n = 23, that is, there are 23 pairs of chromosomes that determine our characteristics. To see better, observe this human karyotype (exam for identification of chromosomes) below:

What-are-chromosomes-autosomes-examination-of-karyotype-human-complete-male

Each streak is a cluster of DNA strands, that is, a chromosome. It carries all of your information and is present in all the nuclei of your cells. They are your “molecular fingerprint”!

A man and a woman have their own karyotype, each with 23 pairs. When they reproduce, they also have a child with 23 pairs. For this reasoning, we know that cell reproduction of gametes cannot be mitosis, otherwise the child would be born with 46 pairs - which does not belong to the human species.

Therefore, male and female gametes reproduce by meiosis, that is, they reduce their number of chromosomes in half and, alone, are unable to form anything.

But, when they unite, they will form an embryo, that is, there will be a new individual with 23 pairs, a karyotype of its own, which will express the characteristics. Therefore, each chromosome pair of a child is formed by a chromosome of the mother and another of the father, generating a being completely unique and different from its parents.

As you may have noticed, the last pair, number 23, has a different shape from the others.

What are autosome chromosomes?

All the first 22 pairs of human chromosomes are called autosome chromosomes. This means that they will develop characteristics that are common to all individuals of that species.

Let’s take the example:

Let’s assume that pair number 2 is where the information is that will make the human intestine be formed and pair number 16 is where the height is. We know that having a human intestine and having a height are characteristics common to all individuals of this species, whether male or female.

There are small variations precisely because each being is unique, that is, it is the combination of two other unique beings. They occur in even smaller parts - within each chromosome - and we study them in Mendel’s Laws!

The fact is that there are basic characteristics that group that species, whether male or female, and it is the autosomal chromosomes that are responsible for this!

What are sex chromosomes?

Now that you know what autosome chromosomes are, we can see the next type: sex chromosomes (or heterosomes).

Pair number 23, which are represented by letters (X and Y), are responsible for telling which gender that individual belongs to male or female.

  • When the pair is formed by 2 X chromosomes, it belongs to the female sex (XX).
  • When the pair is formed by an X and a Y, it belongs to the male sex (XY).

As you can see, the Y chromosome is a little smaller and it is he who will trigger male characteristics: high testosterone production, denser bones, etc.

The presence of 2 X chromosomes will trigger female characteristics: developed breasts, more open pelvis, high estrogen production, etc. The X chromosome alone triggers characteristics such as the presence of breasts. As the woman is formed by a pair of X chromosomes, the breasts develop in her and the man does not.

What is the difference between chromosome and chromatin?

The two structures are composed of DNA, the difference between them is the state in which they are.

Chromatin corresponds to a long, thin strand of DNA, found during interphase when the cell is not dividing.

Each chromatin strand constitutes a chromosome. The chromosome is the chromatin “wrapped” on itself, taking on a spiralized and condensed shape when the cell divides.

Therefore, the chromosome corresponds to condensed chromatin. To get an idea of ​​the degree of condensation, the chromosome is the only structure visible during cell division.

Chromosome Formation

A chromosome can be demarcated along its length in thousands of regions called genes .

The function of chromosomes is to control the functions of cells. In addition, they carry an individual’s genetic information through genes.

Structure

The chromosome has a filamentous structural unit of DNA in the form of a spiral, being surrounded by a protein substance called a matrix.

Chromosome Parts

The parts of the chromosome are:

  • Chromomers: These are very irregular thickenings with a granulation aspect, present in the entire length of the chromatin;

  • Chromatids: They are the result of the longitudinal division of the chromosome during cell division;

  • Centromere: Primary constriction that divides the chromosome into 2 arms and influences movement during cell division. In general, there is a single centromere per chromosome, although there are dicentric or polycentric organisms;

  • Satellite: Terminal part of chromosomal material separated from the chromosome by a secondary constriction;

  • SAT zone: Portion of the chromosome related to the formation of the nucleolus during telophase;

  • Telomeres: Final ends of the chromosomes that protect it from degradation.

In the metaphase and anaphase of cell division, the chromosome filaments are more compact and condensed, making them easier to study.

DNA and Histones

The association between DNA and histone proteins is another important aspect in the structure of chromosomes.

They form a complex since histones are positively charged and the phosphate groups of DNA have negative charges.

There are 5 different types of histones (H1, 2 H2A, 2 H2B and 2 H3), which are distinguished according to the lysine/arginine ratio.

Histones increase the diameter of DNA and also alter its physical properties.

For example, the melting temperature, at which the DNA strands change from the regular double helix to the single strand form, is greatly increased due to histones.

Types of Chromosomes

Chromosomes are classified according to the position of the centromeres.

  • Metacentric : Centromere in the middle position. The two arms are the same size.

  • Acrocentric : Centromere near one end of the chromosome. One arm is large and the other is smaller.

  • Telocentric : Centromere at one end. The chromosome has a single arm;

  • Submetacentric : Centromere slightly displaced from the median region. The arms are in uneven sizes.

Types of Chromosomes

Human Chromosomes

The set of chromosomes of a species is called a karyotype.

Thus, the human karyotype has 23 pairs of chromosomes. In diploid organisms, somatic cells have 2n chromosomes, because 23 chromosomes were of maternal origin and the other 23 were of paternal origin.

Thus, a total of 46 chromosomes received. Of these, 44 are autosome chromosomes, found in all somatic cells. Meanwhile, 2 of them are sex chromosomes, with “X” being the female chromosome and “Y” being the male chromosome.

Women have pairs “XX” and men “XY”.

Human karyotype of a male individual

Human karyotype of a male individual

Any type of change in the number and structure of chromosomes causes the mutation.

An example of a mutation is Down’s Syndrome caused by the presence of an extra chromosome in pair 21, hence it is also known as Trisomy 21.

Homologous chromosomes

The homologous chromosomes have the same size and maintain the same relative positions of the centromeres.

Homologous chromosomes are related to the Allele Genes. These genes occupy the same gene locus on homologous chromosomes and are involved in determining the same character.

The syndromes generated

When changes in chromosomes occur, consequences in the body can develop. These changes can be structural or numerical. The structural one is about changing the size or shape of the chromosome. This process is generated due to the deficiencies caused during the process of duplication, inversion or also translocation.

The numerical changes correspond to the increase or decrease in the amount of normal karyotype of the individual. These changes are classified into euploidies and aneuploidies.

Euploidies: in this process, there is an increase or loss of chromosomes in the genome;

Aneuploidies: there is already a chromosome increase or decrease process.

Numeric aneuploidy changes are responsible for generating Down’s syndrome and Turner’s syndrome.

Down Syndrome

As mentioned, the human being has 23 chromosome pairs, with a total of 46. The individual who has Down’s Syndrome has one more chromosome in the pair - 21 (2n + 1). It is for this reason that it is also called the 21 trisomy.

People who have Down’s syndrome have, for example, a single line on the palm of their hand. In addition, they usually have short stature and eyes pulled up. People who have trisomy 21 are prone to develop heart, lung and respiratory problems.

In summary, this syndrome concerns a genetic mutation in pair 21. There is no cure, however, treatments can be performed, for example, physiotherapy.

Klinefelter Syndrome

Klinefelter Syndrome is also an alteration in the chromosome that concerns the presence of an extra X chromosome. This condition affects only men and can cause, for example, infertility and malformation of the genital organ.

Turner’s syndrome

There is also the Turner Syndrome, a condition caused to the detriment of the numerical alteration aneuploidies. This syndrome occurs only in women and is generated due to the absence or lack of part of the X sex chromosome, that is, 2n - 1.

One of the characteristics of those who have the syndrome is the excess skin on the neck. In addition, other aspects of the affected people are related to the existence of the enlarged chest and breasts.

Conclusion

The chromosomes correspond to filaments that have the power to multiply and divide, and are present in the cell nucleus. The human being has 46 chromosomes organized in 23 pairs.

The basic response to the number of chromosomes do people have is that individuals have 23 sets of chromosomes. It makes an aggregate of 46 chromosomes.

DNA, Chromosomal primary unit

DNA, Chromosomal primary unit

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Out of these 23 sets, 22 sets are comprising of autosomal chromosomes and the 23rd pair of chromosomes addresses the sex chromosomes.

Chromosomes are the fundamental piece of the legacy and are liable for the exchange of attributes from guardians to posterity. X and Y chromosomes are answerable for the assurance of the sex of the future.

What are chromosomes?

:star: Chromosomes are genetic units and are made out of qualities. Chromosomes are string like designs that are available in the cores of people, creatures, and plant cells.

:star: Word “Chromosome” is begun from the Greek language. Chrome implies shading and soma implies body. Thus, the chromosome is aggregately signifying “shaded body”.

:star: This term was credited to this genetic construction as a result of explicit staining of chromosomes when colors are applied and the reality was seen by certain researchers.

:star: While discussing the primary cosmetics of chromosomes, they are comprised of protein and Deoxyribonucleic corrosive (DNA) particle.

:star: Unique qualities that are ascribed to every individual are conveyed as a message covered up in DNA that is moved from guardians to the youngsters.

:star: 23 sets of chromosomes that make an aggregate of 46 chromosomes are the real source to convey the hereditary data from guardians to youngster through the interaction of heredity.

:star: Details that are available in the hereditary message conveyed by DNA - that structures chromosomes - are answerable for the remarkable qualities of every person that are totally not quite the same as others.

:star: what number chromosomes are available in the cell of a life form – regardless of whether individuals or plants, decide in which sense and to which degree they will be not the same as one another.

:star: For instance, on the off chance that we think about certain types of creepy crawlies, they may have only a couple of chromosomes while some bigger creatures, for example, giraffes have 31 sets of chromosomes making a sum of 62.

:star: Similarly, some different creatures yet have a shifted scope of chromosomes. All species, including people, have a diploid number of chromosomes.

Chromosomes, sister chromatids

Chromosomes, sister chromatids

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:star: It implies that chromosomes are available in type of coordinating with sets, you can contrast them and a couple of socks or gloves that are actually like one another and serve inseparably to play out their capacity.

:star: In each pair, one chromosome is acquired from each parent during the cycle of preparation. While thinking about the quantity of chromosomes in the cells of people, every human cell has 23 sets and a sum of 46 chromosomes.

:white_check_mark: Autosomal chromosomes: While elaboration further, among these 23 sets, 22 sets are alluded to as autosomes as they don’t have anything to do with the assurance of sex of the posterity.

:white_check_mark: Sex chromosomes: One sets of chromosomes that is comprising of X-chromosome and Y-chromosome are known as sex chromosomes and this lone pair characterizes the sex of posterity.

:star: When there is any issue in this pair of chromosomes, it brings about sex-connected issues that are moved from one age to another, for example, hemophilia is such a clinical oddity that communicates in ages if present in the guardians.

:star: In this XY pair, the X chromosome is given by a female parent while the Y chromosome comes from the male parent. DNA and proteins are the primary units of chromosomes while an extraordinary segment of DNA is alluded to as a Gene.

:star: Genes are available as quality sets at the uncommon focuses that are known as loci. Overall, all the hereditary material is named as genome and genome is the planning material of posterity.

:star: Nowadays, a few chromosome-connected sicknesses are being dealt with in light of profound hereditary examination. At the point when hereditary examinations are accomplished for different people, it permits the researchers that are considering hereditary qualities to discover the qualities that are answerable for various ailments.

:star: Studying the hereditary cosmetics of individuals, assists researchers with thinking of explicit medicines for deadly illnesses that are explicitly focusing on that individual’s genome. For the most part the problems that are being dealt with or are planned to be dealt with are hereditary issues, for example, sickle cell sickliness or thalassemia.

:star: Other than these two issues, there are a few issues that are brought about by the issues in hereditary grouping, accurately known as “Hereditary mistake”. One such model is diabetes in which the qualities that are liable for insulin amalgamation are not appropriately sequenced and thus it brings about Diabetes mellitus.

:star: A superior treatment system is possibly planned on the off chance that you know the problem and its underlying foundations profoundly and plainly. That is the explanation, researchers and analysts are centering the hereditary examination more than before to come out with focused medicines.

Disclosure of chromosomes

:white_flower: what number chromosomes are available in the human body and how are they organized are the focuses to be considered for understanding the issues and planning the medicines.

:white_flower: Chromosomes are too little to even think about being seen by the unaided eye and henceforth the researchers who study heredity, take a gander at cells and cell materials in the magnifying instrument. The principal cell was taken a gander at by magnifying instrument in the last part of the 1800s and around then, cell study was a serious striking disclosure.

:white_flower: Initially, there were no subtleties accessible in regards to the construction and capacity of a cell and the cell particles, be that as it may, with the headway in cell examines, presently pretty much everything about cells is in information.

:white_flower: Methodology and innovation continued creating and in the twentieth century, researchers had a vastly improved comprehension of atomic material comprising of chromosomes.

:white_flower: The chromosomal examination gave researchers a greatly improved and clear vision about the connection between the issues during legacy and their appearance in the ages.

:closed_book: Read Also :point_down:

Do all cells have DNA?

How would you decipher DNA into mRNA?

What is legacy and quality articulation?

Construction of chromosomes

:white_flower: For a superior comprehension of chromosomes and qualities and their legacy in ages, the initial step is to comprehend the construction of chromosomes.

:white_flower: If we think about an individual chromosome, it’s too little to even consider being seen with the unaided eye. By utilizing a magnifying lens at first and an electron magnifying instrument recently, researchers came out with a reasonable primary investigation of this legacy material.

:white_flower: Two significant parts that structure a chromosome are protein and deoxyribonucleic corrosive – DNA. One DNA atom is utilized in the arrangement of a solitary chromosome and DNA is available in curled structure around the bigger protein – histone protein.

Chromosomes, hereditary qualities

Chromosomes, hereditary qualities

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:question: What if DNA isn’t snaked around protein?

:white_flower: Well, DNA is made out of more modest subunits and one DNA can have a length of 6 feet on the off chance that it is set uncoiled. For better fitting in the cell core, DNA is snaked around the protein and consequently can be fitted in the core.

:white_flower: While discussing the design of DNA, it is available as a twofold helix or like two springs that are curled around one another. Either side of this contorted helix is comprising of a nucleotide base and a spine comprised of sugar-phosphate.

:white_flower: Four fundamental nucleotide bases that are participating in the design of DNA are:

Adenine – truncated as A

Guanine – truncated as G

Cytosine – truncated as C

Thymine – truncated as T

:white_flower: The primary gathering of these bases in the helix assumes the principle part in the development of a twofold helix – a trademark state of DNA. Bases are gathered so that adenine is fortified with thymine and cytosine is available before guanine framing a connection in the middle of them.

:white_flower: If there is any issue in the connecting of nucleotide bases, for example, if An isn’t framing a linkage with T, or G isn’t connected with C, there will be a wreck during the interaction of mitosis. Mitosis is the real interaction that frames the base of cell division.

:white_flower: During mitosis, DNA that is available as a twofold helix is uncoiled, and the two uncoiled strands at that point structure new strands corresponding to every one of them.

Codons: Genetic Codons are the grouping of base combines that are the essential formula for the combination of proteins. Three base sets are consolidated to frame a solitary codon and diverse amino acids – that are building squares of proteins – are then shaped by the directions present in type of codons.

:white_flower: For instance, amino corrosive glycine is framed by a codon that has a nucleotide base grouping as GGG, i.e., three guanine bases are making a codon.

:white_flower: The formula for every protein is available in a quality and the human genome is the fundamental capable factor for the amalgamation of proteins in the body.

:white_flower: Proteins are then allocated various capacities in the body, for example, keratin protein is participating in the assembling of hair and insulin is being utilized for controlling glucose level.

:white_flower: Almost every one of the capacities that are being completed in the body are including the utilization of proteins. For example, chemicals, which are the significant impetuses in the biochemical responses occurring in the body are proteins naturally.

:white_flower: Hemoglobin is a significant segment of blood and antibodies that make the guard arrangement of the body are likewise proteins. Consequently, it tends to be said that chromosomes – fundamental inherited material – are characteristics.