Chromosome Number in Humans – Information at a GlanceÂ
The chromosome number in humans is 23 pairs. Normally, there are 46 chromosomes in total in each cell in humans. Twenty-two of these 23 pairs are referred to as autosomes and are the same in both females and males. However, the difference is in the last pair of chromosome – 23rd pair. It differs in females and males. They are the sex chromosomes determining the sex of an individual.
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| Species | Humans |
| Ploidy | Diploid (Somatic cells)
Haploid (sex cell) |
| Chromosome number | 46 or 23 pairs |
| Representation | 2n=46
2n – diploid (somatic cells) n – haploid (sex cells) |
Ploidy of Humans
Ploidy is the number of sets of chromosomes in the nucleus of a cell (genome) of an entity. It is denoted by “n”.
In humans, the chromosomes can be categorised into the following two types:
- Allosomes (gametes or sex chromosomes)
- Autosomes (body chromosomes)
Some of the genetic characteristics are associated with the sex of an individual and are inherited through the sex chromosomes. The autosomes comprise the remaining genetic hereditary instruction. All of these tend to behave in the same way at the time of cell division.
The monoploid number(x) in humans is equivalent to the haploid number (n); this is to say that x = n = 23. The diploid (2n) cells possess two homologous copies of each of the chromosomes, one each from each of the biological parents. The exact number of chromosomes can be one or two different from the 2n number; still, the cells can be categorised as diploid. The majority of mammals are diploid entities, even though all the individuals possess some part of cells that show polyploidy. The human diploid cells possess 46 chromosomes, and the human haploid gametes (Sperm and egg) comprise 23 chromosomes.
Pairs of Chromosomes in Human Body
| Chromosome number/name | Number of genes | Base pairs |
| Chromosome 1 | Over 3000 genes | Over 240 million base pairs, of which approximately 90% are known |
| Chromosome 2 | Over 2500 genes | Over 240 million base pairs, of which approximately 95% are known |
| Chromosome 3 | Approximately 1900 genes | Close to 200 million base pairs, of which approximately 95% are known |
| Chromosome 4 | Approximately 1600 genes | Close to 190 million base pairs, of which approximately 95% are known |
| Chromosome 5 | Approximately 1700 genes | Close to 180 million base pairs, of which approximately 95% are known |
| Chromosome 6 | Approximately 1900 genes | Close to 170 million base pairs, of which approximately 95% are known |
| Chromosome 7 | Approximately 1800 genes | Close to 150 million base pairs, of which approximately 95% are known |
| Chromosome 8 | Approximately 1400 genes | Close to 140 million base pairs, of which approximately 95% are known |
| Chromosome 9 | Approximately 1400 genes | Close to 130 million base pairs, of which approximately 85% are known |
| Chromosome 10 | Approximately 1400 genes | Close to 130 million base pairs, of which approximately 95% are known |
| Chromosome 11 | Approximately 2000 genes | Close to 130 million base pairs, of which approximately 95% are known |
| Chromosome 12 | Approximately 1600 genes | Close to 130 million base pairs, of which approximately 95% are known |
| Chromosome 13 | Approximately 800 genes | Close to 110 million base pairs, of which approximately 80% are known |
| Chromosome 14 | Approximately 1200 genes | Close to 100 million base pairs, of which approximately 80% are known |
| Chromosome 15 | Approximately 1200 genes | Close to 100 million base pairs, of which approximately 80% are known |
| Chromosome 16 | Approximately 1300 genes | Close to 90 million base pairs, of which approximately 85% are known |
| Chromosome 17 | Approximately 1600 genes | Close to 80 million base pairs, of which approximately 95% are known |
| Chromosome 18 | Approximately 600 genes | Close to 70 million base pairs, of which approximately 95% are known |
| Chromosome 19 | Approximately 1700 genes | Close to 60 million base pairs, of which approximately 85% are known |
| Chromosome 20 | Approximately 900 genes | Close to 60 million base pairs, of which approximately 90% are known |
| Chromosome 21 | Approximately 400 genes | Close to 40 million base pairs, of which approximately 70% are known |
| Chromosome 22 | Approximately 800 genes | Close to 40 million base pairs, of which approximately 70% are known |
| Chromosome X | Approximately 1400 genes | Close to 150 million base pairs, of which approximately 95% are known |
| Chromosome Y | Approximately 200 genes | Close to 50 million base pairs, of which approximately 50% are known |
Human Genome
The human genome comprises 3 x 109 nucleotide pairs, and one strand of these many nucleotides would approximately be 2 metres in length. The nucleus of a typical cell in humans is approximately 5-8 micrometres in diameter.
The DNA of humans should be packed into a nucleus that is about 5 micrometres in diameter, which indicates that it is highly compressed. This is made possible by coiling the DNA around the nucleosomes and then enclosing it in helical filaments.
Chromosome number – Number of Human Chromosomes
Human cells have 23 pairs of chromosomes – 22 pairs of autosomes (diploid) and one pair of allosomes or sex chromosomes (haploid). This makes up for a total of 46 per cell. Males have one X and one Y chromosome, while females possess two copies of X chromosomes. Additionally, human cells can have several copies of the mitochondrial genome.
Each copy of the chromosome is inherited from the biological parents – the female parent and the other from the male parent. Subsequently, the offspring inherits some traits of their father and some of their mother. There is a difference in the pattern of inheritance for the smaller circular chromosome seen in the mitochondria. At the time of fertilization, it is only the egg cells (not the sperm cells), which retain their mitochondria. Thereby, the mitochondrial DNA is always inherited from the mother, the female parent. A few conditions in humans, even some forms of diabetes and hearing impairments, have been linked with the mitochondrial DNA.
Inaccurate Inheritance
The consequence of inheriting an insufficient or exceeding number of copies of sex chromosomes can be serious. For instance, those females who have inherited extra copies of X chromosomes usually are taller compared to the average, and some even are mentally retarded.
The males possessing more than one X chromosome have Klinefelter syndrome. It is a condition distinguished by a tall build, and in most cases, has impaired fertility.
Another condition that is a result of an imbalance in the number of allosomes is Turner syndrome. Those women who have Turner syndrome have only one X chromosome. They are distinguished by short stature and generally do not experience puberty; some have heart and kidney problems too.
This was brief on the number of chromosomes in humans. For related information, visit BYJU’S.
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Frequently Asked Questions
How many chromosomes do humans have?
Each cell in humans generally has 23 pairs of chromosomes, totally 46 in number. Out of these 23 pairs, 22 pairs of chromosomes are autosomes. The last pair, 23rd pair are the sex chromosomes differing in males and females.
What happens if one has an extra chromosome, 47 chromosomes?
An extra chromosome leads to a trisomy – a chromosomal condition. A person having trisomy has 47 chromosomes instead of the normal 46 chromosomes. An example of trisomy is Down syndrome.
What are chromosomes made of?
Each chromosome comprises a DNA that is tightly coiled several times around proteins referred to as histones accommodating its structure.
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