Question

Consider what you learned about dominant and recessive alleles in Concept 14.1. If a disorder were caused by a dominant X-linked allele, how would the inheritance pattern differ from what we see for recessive X-linked disorders?

Short answer

In both recessive, dominant X-linked disorders, males express the trait because they possess just one X-chromosome. On the other hand, females can be a carrier or diseased in case of recessive X-linked disease but diseased in dominant X-linked conditions because one dominant allele is enough to cause the disease.

Step-by-step solution

Dominant and recessive alleles

There are two alternative forms of a gene; these are called alleles.Out of the two alleles, one is dominant, and the other is recessive.The allele that determines the trait of an organism is dominant alleles, whereas the other allele which does not have any effect on the trait is recessive alleles.

Any individual who possesses one dominant and one recessive allele is called heterozygous, whereas individuals with either both dominant or recessive alleles are called homozygous.

Inheritance of recessive X-linked disease

Recessive X-linked disease is caused by the inheritance of two recessive alleles.In contrast, an individual with one recessive allele is a carrier for the disease.

In this condition, males having recessive alleles will express the trait because they are hemizygous. While females who receive one recessive would be the carrier for the disease, and those who receive both the recessive alleles express the trait. Thus, females have an advantage here due to the presence of two recessive alleles.

Inheritance of dominant X-linked disease

Dominant X-linked disease is caused by the inheritance of just one dominant allele.Individuals receiving one dominant allele express the trait. Thus,an individual cannot be a carrier for a dominant X-linked trait.

In this condition, males transmit the dominant allele to the daughter, and, thus, daughters are diseased. At the same time, females with dominant alleles will transmit half of the alleles to sons and half to daughters.

Difference between the two inheritance patterns

Males receiving defective alleles in both recessive and dominant X-linked disorder express the trait because they have just one X chromosome, which causes the disorder. As a result, males have more X-linked disorders.

On the other hand, females receiving recessive alleles can be carriers for recessive X-linked disorder but are diseased with just one dominant allele in dominant X-linked conditions.