Sex Chromosomes Every cell in human body has DNA that is tightly packed into compact structures called chromosomes. They are present inside the nucleus of the cell. There are 23 pairs of chromosomes of which 22 pairs are called autosomes and the 23rd pair is called allosome or sex chromosomes Autosomes Autosomes are homologous pairs, which transfer genetic information from the parents to the offspring.
Each pair of chromosome contains all the genes that are responsible for the existence of the life. There are 22 pairs of autosomes in every cell.
In each pair, the chromosomes are of the same length, with the centromere placed in the same location. During mitosis, these chromosomes are duplicated and transferred to two daughter cells.
So the new daughter cells get a complete copy of chromosomes containing the genetic information from the parent cell. Autosomes are labeled from 1 to 22, based on number of base pairs present within them. This TDF transcription factor plays an important role in determining male sex. Mutations on SOX9 gene in humans with a Y chromosome leads to the development of female offspring.
Allosomes or sex chromosomes The 23rd pair of chromosomes present in humans is called the allosomes. They differ in size and function when compared to autosomes. They determine the sex of an individual. They are labeled using letters X and Y.
Allosomes in females comprise two X chromosomes, and in male it comprises of one X chromosome and one Y chromosome. Unusual combination of allosomes result in disorders like colour blindness, haemophilia, Fragile X syndrome.
Males and female gametes The gametes sperms in male and egg in female are haploid cells. Haploid cells are those that have only one set of chromosomes 23 chromosomes. All female gametes have 22 autosomes and one X chromosome.
Male gametes are of two kinds, one kind with 22 autosomes and one X chromosome, and the other kind with 22 autosomes and one Y chromosome. When the male and female gametes fuse during sexual reproduction, a new offspring having 46 chromosomes is produced. If the male gamete with an X chromosome fuses with the female gamete, it results in the formation of a female offspring.
If the male gamete with a Y chromosome fuses with the female gamete, it results in the formation of a male offspring.