Q: What is sex linkage?
A: Sex linkage is a term that describes the inheritance of traits or conditions that are controlled by genes on the X chromosome.
Q: How does the sex determination system work in mammals?
A: Mammals have an XX/XY system of sex determination, where females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).
Q: Why is the X chromosome important in sex linkage?
A: The X chromosome has many more genes than the Y chromosome, and therefore carries a larger portion of the genetic information.
Q: What are recessive alleles?
A: Recessive alleles are forms of a gene that are only expressed when an individual has two copies of the allele, one inherited from each parent.
Q: How are traits like colour blindness and haemophilia caused by sex linkage?
A: These traits are caused by recessive alleles that are carried on the X chromosome. As males only have one X chromosome, they are more likely to exhibit the trait if they inherit the recessive allele from their mother.
Q: Why do females carrying the mutant allele for sex-linked conditions usually not show the condition?
A: Females have two X chromosomes, so even if one carries the recessive allele, the other X chromosome can compensate by carrying a dominant allele that expresses a normal phenotype.
Q: Why will a male develop a sex-linked condition if he carries the mutant allele?
A: If a male carries the mutant allele on his X chromosome, it will be expressed because he does not have a second X chromosome that can provide a dominant allele for that gene.
