Why is a pair of sex chromosomes in human beings called amismatched pair in terms of type and size ?

In humans, a pair of sex chromosomes is referred to as a mismatched pair in terms of type and size due to the differences in their physical characteristics and the genes they carry.

1. Type: Humans have two types of sex chromosomes, X and Y. Females have two X chromosomes (XX) and males have one X and one Y chromosome (XY). The X chromosome carries around 1,000-2,000 genes, many of which are not related to sex determination. The Y chromosome is much smaller and carries around 50-60 genes, most of which are related to sex determination and sperm production.

2. Size: The X chromosome is significantly larger than the Y chromosome. The X chromosome is about 155 million base pairs long, while the Y chromosome is about 59 million base pairs long. This size difference is another reason why they are referred to as a mismatched pair.

3. Gene content: The X chromosome contains more genes compared to the Y chromosome. Many of these genes are responsible for non-sexual characteristics. On the other hand, the Y chromosome contains fewer genes, most of which are responsible for determining male sexual characteristics.

In conclusion, the term "mismatched pair" refers to the differences in type, size, and gene content between the X and Y chromosomes in humans.