AGB 121: Principles of Animal Genetics and Population Genetics (2+1)

SEX LINKAGE

• There are two types of chromosomes,
  • Autosomes and
  • Sex chromosomes
• Autosome refers to those chromosomes that are not involved in sex determination.
• Sex chromosomes determine the sex of an organism. A human somatic cell has two sex chromosomes: XY in male (hetero-gametic) and XX in female (homo-gametic).
• In birds the female (ZW) is hetero-gametic and male (ZZ) is homo-gametic.

Sex linkage

• Sex chromosome contains genes not only for sex but also for other traits.
• Sex linkage refers to the association or linkage of a hereditary trait with sex chromosomes.
• Most traits carried are present only on the X-chromosome.
• The Y-chromosome is smaller, and so, very few genes are located on this chromosome.
• Because of their location in the sex chromosomes, they are said to be “sex linked traits”.