Epistasis, Pedigree Analysis and the Genetics of Sex

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Sex chromosomes:

A male needs only 1 copy of a recessive allele to display the phenotype. A female needs 2 copies. Therefore, males are more likely to display recessive traits.

Ex. Sex-influenced traits

Females:

AA > normal
Aa > normal
aa > bald

Males:

AA > normal
Aa > bald
aa > bald

Epistasis: interaction of different loci

Ex. AA or Aa > round
aa > wrinkled
BB or Bb > yellow
bb > green

If you cross: AaBb * AaBb

9 AABB or AABb or AaBB or AaBb (round, yellow)
3 AAbb or Aabb (round, green)
3 aaBB or aaBb (wrinkled, ...