Exam 2: Set 1: X-Linked Recessive

sex-linked genes

genes found on one or both of the sex chromosomes

X/Y-linked genes

found on the X or y chromosome respectively

sry gene

codes for the SRY transcription factor that causes male embryonic development

what happens if an XY embryo has a LOF mutation on the sry locus?

The embryo will be phenotypically female since the SRY transcription factor won’t trigger male development

X-linked inheritance patterns

Males only need one copy of the LOF mutation to have the phenotype. Females need two copies (one on each X chromosome)

Hallmarks of x-linked recessive pattern of inheritance

Males are primarily affected and typically have an unaffected mother.

If a female is affected, her father is always also affected.

Approximately half of a carrier female’s sons will be affected

why is an x-linked recessive disorder never passed from father to son?

Males get their X chromosome from their mother, meaning if their mother has no LOF alleles, the sons must also be unaffected

why are all daughters of an affected male, carriers for an x-linked recessive disorder?

Since they receive one of their X chromosomes from their father, and he has only one LOF allele on his single X-chromosome, they must have received one LOF allele.

what are the two x-linked recessive disorders you must know?

red-green colorblindness and hemophilia