Allosomes and Other Traits
So far, we've explored traits on the 22 pairs of chromosomes that are not allosomes. But what are allosomes? Allosomes are special in that they are the chromosomes that carry gender/sex information. And while you can get other traits from either of your parents, allosomes contain traits that are linked to your gender.
Sex-linked genes/alleles are genes carried by either sex chromosome. Because only men inherit Y chromosomes, only men get traits linked to the Y chromosome. However, since men also have 1 X chromosome, they have a 50/50 chance of getting either of their mother’s X chromosomes. The father cannot provide an X chromosome to a boy, because if he did the boy would be XX—and not a boy! A girl will always receive one X chromosome from her father and one of her mother’s X chromosomes. This means she will always get her father’s dominant X-linked traits, and a 50% chance of getting either of her mother’s chromosome.
Sex-linked genes/alleles are genes carried by either sex chromosome. Because only men inherit Y chromosomes, only men get traits linked to the Y chromosome. However, since men also have 1 X chromosome, they have a 50/50 chance of getting either of their mother’s X chromosomes. The father cannot provide an X chromosome to a boy, because if he did the boy would be XX—and not a boy! A girl will always receive one X chromosome from her father and one of her mother’s X chromosomes. This means she will always get her father’s dominant X-linked traits, and a 50% chance of getting either of her mother’s chromosome.
For example, if a mother carries (but does not show) a recessive, X-linked allele for a trait but the father does not, the boys will have a 50% chance of getting that trait (50% of getting each of the mother’s X chromosomes). 50% of the girls carried the recessive X(a) allele, and 50% of the boys showed X(a) in their phenotype
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