Sexlinked Traits What is SexLinked Inheritance Sexlinked inheritance

Sex-linked Traits

What is Sex-Linked Inheritance? Sex-linked inheritance is different from other types of inheritance because your gender plays a significant role in the chances of inheriting a particular trait or a disease.

What is sex-linked? Sex-linked genes are found on X chromosomes Females have XX chromosomes Males have XY

How does sex-linked inheritance work? Because females have two X chromosomes, they are usually at an advantage in terms of inheriting “bad” genes located on the X chromosome because they will have to get it on BOTH X chromosomes. If girls inherit one of these genes on one X chromosome, they may have another X chromosome with the normal gene that will mask the effects of the “bad” gene. Males, on the other hand, have only one X chromosome. If they inherit a “bad” gene from their mom (the X chromosome), they are stuck with that particular trait or disease

What traits are carried on X chromosome? Blood clotting and normal color vision are two genes carried on the X chromosome of all humans. Hemophilia (the inability to make platelets so your blood clots when you get cut) and colorblindness occur when a person inherits a mutated and recessive version of this gene.

Female Genotypes: Hemophellia Female with normal blood clotting ability (Homozygous dominant) X NX N Female with normal blood clotting ability (Heterozygous) X NX n Female with hemophilia (Homozygous recessive) X n N = normal n = hemophellia

Male Genotypes Male with normal blood clotting ability X NY Male with hemophilia X n. Y **Notice the Y chromosome never gets a letter – you simply carry it through the punnett square

Practice Problem #1 A female who is heterozygous for hemophilia marries a man who has normal blood clotting ability. Make a punnett square and list their genotype and phenotype ratios.

Practice Problem #2 A homozygous normal female and a male with hemophilia have children. We are the genotype and phenotype ratios of their offspring?

Color-blindness In order for a woman to be colorblind, she must inherit the colorblindness gene on both of her X chromosomes. For males, they only need to inherit one copy in order to exhibit the trait.

Genotype: Female with normal color vision (Homozygous dominant) X CX C Female with normal color vision (Heterozygous) X CX c Female with colorblindness (Homozygous recessive) X c

Genotype: Male with color vision X CY Male with colorblindness X c. Y

Practice Problem #3 Cross a female who is colorblind with a male with normal color vision. What are the genotypes and phenotypes of their children?

Practice Problem #4 If a colorblind son from the previous problem has children with a woman with normal color vision (homozygous dominant). What percentage of the SONS is colorblind? Make a punnett square to find out.