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A little more on genetics… 4-4

Some vocabulary: Generations: P1 = Parent generation (1st in a cross) F1 = First filial (offspring of P1) F2 = Second filial (offspring of F1) Locus = the location of a gene on a chromosome

Mendel’s Work Principle of Dominance and Recessiveness Bred different phenotype plants (ex. T= tall, t = short) by cross-pollination: P1 Pure tall (TT) X Pure short (tt) F1 All Tall (Tt, Tt) F2 ¾ Tall (TT or Tt), ¼ Short (tt)

P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

He repeated this with 7 different traits and always got the same ratio in F2 Therefore: “Factors” (now called genes) control each trait. Trait appearing in F1 is DOMINANT (ex. tall) Trait reappearing in F2 is RECESSIVE (ex. short)

Punnett squares: Method used to predict the outcome of genetic crosses One-Factor cross = one trait Monohybrid cross– both parents heterozygous

Testcross To figure out the Genotype of a parent, cross with a homozygous recessive parent and analyze offspring. Ex. A man with free earlobes wants to know if he is homozygous or heterozygous. He marries an attached earlobed woman and has kids. The first kid he has displays attached earlobes The man has thus found out that he is heterozygous