Question

Distinguish between X and Y chromosomes. (Mention any ‘two’ points).

Answer 1

Hint: Insights of the sequencing of the human genome has shown that the smallest chromosome in humans has the least number of genes. The X chromosome has a small amount of heterochromatin and the Y chromosome has a large amount of heterochromatin.

Complete answer: Humans have 23 pairs of autosomes and one pair of sex chromosomes. Females have two copies of the X chromosome and males have only one X chromosome. Only one X chromosome is functional in females. The Y chromosome is a male determining gene because male lineage is usually traced using the Y chromosome. Different approaches were used in identifying the number of genes in a chromosome. Genes on sex chromosome help in sex determination and also provides instructions for protein synthesis. The Y chromosome is one of the smallest chromosomes in humans. It has the least number of genes that are approximately 55 genes and the X chromosome has about 900 genes. The Y chromosome typically represents about 2-3 percent of the total DNA in the cells. The non-homologous part of the X-chromosome has a greater number of genes than the Y-chromosome.

Note: The X-chromosome contains a larger number of active genes or DNA. Whereas the Y chromosome has a smaller number of active genes. The Y-chromosome has a limited number of genes because the chromosomal genes have degenerated during evolution. The Y chromosome is also known as the gene-poor chromosome. Much of the Y chromosome is composed of repeating DNA sequences.