Location of Sex-Limited Trait Genes

Genes controlling sex-limited traits are present on:

Correct Answer: Autosomes

From Table 6 in the notes: Genes of sex-limited traits are present on autosomes. Although the genes are carried by both sexes on autosomes, their phenotypic expression is completely limited to one sex due to sex hormones.

Sex-Limited Examples (from notes)

• Milk production — gene present in both bulls and cows, but expressed only in cows
• Semen production — expressed only in males
• Egg production in poultry — expressed only in females
• Baldness in humans
• Secondary sexual characters (udder development, antler growth)
• Responsible for sexual dimorphism

Breeding Implication

Since bulls carry genes for milk yield but cannot express them, a bull's genetic merit for milk production can only be estimated through his daughters — hence progeny testing is the best method for selecting sires for sex-limited traits.