We have discussed how recessive phenotypes are more likely to be expressed in males if the corresponding gene is found on the X-chromosome. For example, one-type of colorblindness is caused by a recessive X linked allele, and this trait is much more common inmales than females. But we have also discussed how, in placental mammals, one copy of each X chromosome is randomly silenced in female cells (X inactivation). This raisessomewhat of a paradox. Why donât half of heterozygous females exhibit colorblindness just like hemizygous males that carry the recessive allele?
a.
Based on your under standing of Xinactivation in placental mammals, provide an explanation for why heterozygous females generally do not exhibit colorblindness despite the random silencing of one X chromosome.
b.How would your answer change if we were talking about a marsupial mammal (inwhich the paternally inherited copy of the X chromosome is inactivated in every cell)? Would you expect half of heterozygous females in a marsupial species toexhibit color blindness? Why or why not?
We have discussed how recessive phenotypes are more likely to be expressed in males if the corresponding gene is found on the X-chromosome. For example, one-type of colorblindness is caused by a recessive X linked allele, and this trait is much more common inmales than females. But we have also discussed how, in placental mammals, one copy of each X chromosome is randomly silenced in female cells (X inactivation). This raisessomewhat of a paradox. Why donât half of heterozygous females exhibit colorblindness just like hemizygous males that carry the recessive allele?
a.
Based on your under standing of Xinactivation in placental mammals, provide an explanation for why heterozygous females generally do not exhibit colorblindness despite the random silencing of one X chromosome.
b.How would your answer change if we were talking about a marsupial mammal (inwhich the paternally inherited copy of the X chromosome is inactivated in every cell)? Would you expect half of heterozygous females in a marsupial species toexhibit color blindness? Why or why not?
