BIOL 200 Lecture Notes - Lecture 6: Blood Type, Penetrance, Allele
Document Summary
Outline: allele lethality, incomplete dominance and codominance, partial (incomplete) penetrance, gene interactions(epistasis and complementation) Imagine that in mice, yellow fur (y) is dominant over gray fur (y) You work with yellow and gray mice and notice: you can never obtain true-breeding homozygous yellow mice, when you cross two heterozygotic yellow mice, your progeny ratio is always 2:1, yellow:gray. The very thing happened to cuenot over 100 years ago: it was determined that homozygous dominant yellow furred mice spontaneously abort during development, and this screws up our mendel based genetic outcomes. Yy mice die so 2/3 of progeny are yy, yellow and 1/3 are yy, nonyellow. When a gene is heterozygotic and there are two different alleles one allele beats the other down and is solely expressed: this is how dominance works at large number of genes, but not always. Blonde hair is no (little) pigment in the hair. Alleles for blonde hair are lack of function ; no pigment.
