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Question
Describe the structure of sex chromosomes with the help of labelled diagram.
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Solution
Structure of X and Y chromosomes:
- The x chromosome is straight, rod-like, and longer than the Y chromosome.
- The x chromosome is metacentric, while the Y chromosome is acrocentric.
- The x chromosome has a large amount of euchromatin (extended region) and a small amount of heterochromatin (highly condensed region).
- Euchromatin has a large amount of DNA material, hence the X chromosome is genetically more active.
- The y chromosome has a small amount of euchromatin and a large amount of heterochromatin, hence it is genetically less active or inert.
- Both X and Y chromosomes show homologous and non-homologous regions.
- Homologous regions show similar genes while non-homologous regions show dissimilar genes.
- Crossing over occurs only between homologous regions of X and Y chromosomes.
- 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.
- 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.
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