Sex-Linked Traits Essential Question: How are dominant and recessive sex-linked traits passed onto offspring?

Sex-linked traits are determined by genes on sex-chromosomes. Most sex-linked alleles (genes) are carried on the X chromosome.

Rett Syndrome is a dominant allele sex-linked trait Rett Syndrome is a dominant allele sex-linked trait. A carrier female conceives a child with an unaffected male. What percentage of their daughters will have Rett’s Syndrome? Rett syndrome is a neurodevelopmental disorder that affects girls almost exclusively.

Two of 4 boxes are females (the two on the left). Of the 2 boxes on the left, only 1 has the dominant allele (R). This means that 1 of 2 females has the diseases. 50%.

If the sex-linked trait is recessive, then males require 1 copy and females require 2 copies.

Hemophilia is a bleeding disorder in which the blood does not clot Hemophilia is a bleeding disorder in which the blood does not clot. Hemophilia affects mostly males. Explain to me why mostly males are affected.

If the sex-linked trait is dominant then ALL of an affected male’s daughters will have the trait. Oddly enough, NONE of the an affected male’s SONS will have the disease unless the mother has it. Why?

X-linked hypophosphatemia is a dominant trait X-linked hypophosphatemia is a dominant trait. If a woman with this disease (carrier) conceives a child with a normal man. What percentage of their daughters will have the disease? What percentage of their sons? 60 seconds…GO!

Creating a pedigree chart. Begin with the parents (P1)

Extend a line to display the children (F1)

Extend a line to display spouse/mates.

Extend line to display the grandchildren (F2).

Shade in boxes to display the presence of a trait.

Full box = has the trait. Half box = carriers the trait.

For autosomal inheritance, males are just as likely as females to have the trait/disease.

For autosomal inheritance, males are just as likely as females to have the trait/disease. For a sex-linked (X-linked) inheritance, one gender will be more likely than another to have the disease. X-linked dominant = more females will have it. Ex. Rett syndrome, Hypophosphatemia, etc. X-linked recessive = more males will have it. Ex. Baldness, Colorblindness, Hemophilia.