- Genes/traits that are carried by the sex chromosomes (X and Y) – Mostly X-linked!
- Sex-linked traits can be Dominant or Recessive. MOST are recessive. Sex-linked that is dominant is VERY RARE.
- More males are affected than females. Why? Because males only have one X chromosome. Y chromosome does not carry versions of the same genes as that of the X chromosome. This is shown below.
- An affected son (X^aY genotype) can have parents who have the normal phenotype. (X^AY, dad) x (X^AX^a, mom – a carrier)
- For a daughter (X^aX^a genotype) to be affected, her father must also have it. Her mother must have it or be a carrier. (X^aY, dad) (X^aX^a or X^AX^a, mom)
- OTHER SEX-LINKED INFORMATION: * The trait often skips a generation from the grandfather to the grandson.
* If a woman has the trait (X^aX^a), ALL of her sons will be affected.
* Pedigrees show only female carriers--no male carriers.
- Examples of Sex-Linked Recessive Disorders: colorblindness, hemophilia, deafness, cataracts, etc.
Parent Tip: Review the logic above to help your child master the concept of sex linked inheritance worksheet.
