Question

Describe the structure of sex chromosomes with the help of labelled diagram.

Answer 1

Structure of X and Y chromosomes:

1. The x chromosome is straight, rod-like, and longer than the Y chromosome.
2. The x chromosome is metacentric, while the Y chromosome is acrocentric.
3. The x chromosome has a large amount of euchromatin (extended region) and a small amount of heterochromatin (highly condensed region).
4. Euchromatin has a large amount of DNA material, hence the X chromosome is genetically more active.
5. The y chromosome has a small amount of euchromatin and a large amount of heterochromatin, hence it is genetically less active or inert.
6. Both X and Y chromosomes show homologous and non-homologous regions.
7. Homologous regions show similar genes while non-homologous regions show dissimilar genes.
8. Crossing over occurs only between homologous regions of X and Y chromosomes.
9. The non-homologous region of the X chromosome is longer and contains more genes than that of a non-homologous region of the Y chromosome.
10. X-linked genes are present on the non-homologous region of the X-chromosome while Y-linked genes are present on the non-homologous region of the Y-chromosome.