Useful Genetics Lecture 4b: Genes on the Sex Chromosomes

Overview

• Focus on genes present on the X and Y chromosomes.
• X chromosome:
  • Similar to autosomes in gene density and function.
  • Approx. 2,000 genes, not specific to sexual development.
• Y chromosome:
  • Contains few genes functioning only in males.
  • Major male phenotype genes are autosomal, regulated by SRY.

Chromosome Details

X Chromosome

• Large, approx. 155 million base pairs.
• Contains about 2,000 genes.
• Functions include:
  • Blood clotting
  • Red-green color vision
  • Muscle function
• X-linked phenotypes are common in males due to inheritance patterns.
• Similar gene density across all autosomes and X chromosome.
• Functions mostly shared between males and females.

Y Chromosome

• Shorter, about 38% the length of the X chromosome.
• Contains only a couple of dozen genes, expressed in males.
• Genes are not crucial for male-specific functions.
  • SRY is the key determinant of maleness.
  • SRY does not activate Y chromosome genes but affects autosomal and X chromosome genes.
• Y chromosome contains many degenerated gene sequences.

Gene Expression

• X chromosomes are inherited like autosomes, with differing gene expression.
• Details on gene expression differences will be covered in Lectures 4C and 4D.

SRY Gene

• Produces SRY protein, a male-specific transcription factor.
• Activates male-specific genes on autosomes and the X chromosome, not on the Y chromosome.

Inheritance

• Further discussion on X and Y chromosome inheritance in modules 7 and 8.

Upcoming Topics

• Next lectures will cover dosage discrepancies of X chromosome genes in males and females.