Mendel and Genetics A little history: Prior to 1820s, people knew about inherited traits and used this concept to raise plants and animals: fast horses would breed fast horses. As far a people, the generally accepted theory was that children were a blend (or combination) of characteristics of both the mother and father: A blonde woman and a dark-haired man would have a baby with brown hair (a mix of blonde and dark hair).

Mendel and Genetics In the early 1800s, a monk by the name of Gregor Mendel changed everything we know about Genetics. Mendel bred and studied pea plants. He noticed that the pea plants had specific traits (characteristics) that were passed on from generation to generation.

Mendel’s Peas – Traits he Studied These traits are physical features of the pea plants: they would produce one or the other feature (white or purple flowers).

What would offspring look like if Mendel bred a yellow and green pea ? First, these plants breed “true”. A plant producing yellow peas will always produce yellow peas. If traits were blended, a plant with yellow peas bred to a plant with green peas would produce yellow-green peas.

What Mendel Observed Seed Color – Breeding a yellow pea and a green pea X This observation was consistent with all traits Mendel observed. Key: P1 = one parent P2 = the other parent F1 = first generation offspring F2 = second generation offspring

Important Questions If the offspring were a blend of the parents, what color would the F1 offspring be? Does one color “disappear” in the F1 offspring? Which color? Does that color “reappear” in the F2 generation?

What Mendel Observed When a plant producing green peas was crossed with a plant producing yellow peas, all the offspring produced yellow peas: In that first generation, not a single plant produced green peas. When the yellow pea plants were bred to each other, the green peas returned! X X

Mendel's work showed: Each parent contributes one factor of each trait to the offspring. The blending theory of inheritance was discounted. Traits are not mixed or combined. Males and females contribute equally to the traits in their offspring. Acquired traits are not inherited.

Mendel’s Laws Law of Segregation: each gamete (sex cell) only receives one copy. Law of Independent Assortment: separate genes for separate traits are passed independently of one another from parents to offspring You get one set of traits from your mother and the same set of traits from your father. translation Traits will not affect each other. If one parent is weaker, their trait will not be affected by the stronger parent.

Vocabulary Trait Alleles Genotype - the genetic make-up of a trait in an organism Phenotype - the physical appearance of the trait in an organism Heterozygous Homozygous