Sex-linked inheritance

• Sex-linked genes are located on sex chromosomes
• XX = female
• XY = male
• X^A = normal allele on X chromosome
• X^a = affected allele on X chromosome
• Female can either have X^R X^R or X^R X^r
• Male can only have either X^RY or X^rY
• X^RX^r is a carrier for a trait meaning it won't always express it, just show mild symptoms
• Usually conditions are recessive, meaning in order to express it you must have X^rY or X^rX^r. X^RX^r is a carrier
• If a condition is dominant, it will be expressed through X^RX^r, X^RX^R, and X^RY
• If X-linked inheritance is impossible, then the condition is autosomal
• Any time a child has something and both parents dont have it, the trait is recessive
• If the condition skips a generation, it is recessive
• When the trait is dominant, affected males have only affected daughters
• When the trait is dominant, unaffected females have unaffected sons
• When the condition is recessive, affected mother must have affected sons
• When the trait is recessive, two affected parents have only affected offspring
• When the condition is recessive, heterozygous mothers can have affected or unaffected offspring
• When the trait is recessive, unaffected fathers have only unaffected daughters