1. Observations of the outcomes of simple dominant and recessive
C-13 Mendelian Genetics
Observations of the outcomes of simple dominant and recessive
gene pairings

2. Early ideas of heredity
Constancy of species – heredity occurs within the boundary of the species; not so prior to the Middle ages
(Ex: giraffe and minotaur)

3. View held thru time of Darwin
Direct transmission of traits – child is formed after hereditary material from all parts of parent’s body come together – blending occurs

4. Gregor Mendel Studied garden peas Large # of pea varieties
Peas are small, easy to grow, short generation time
Peas can self-fertilize; bisexual

5. Mendel conducted studies in 3 stages
Self-crossed flowers to make sure white/purple flowered plants were true-breeding
Crossed true-breeding plants (white X purple)
Crossed F1 plants to see traits in future generation (F2 generation)

6. Mendel came to understand….
Plant progeny did not show blending of traits
For each pair of alternative traits, 1 was not expressed in F1, but re-appeared in F2
Traits segregate among the progeny
Alt, traits are expressed in 3:1 ratio in F2

7. The Mendelian ratio
Phenotypic ratio of 3:1
Genotypic ratio of 1:2:1

8. Mendel proposed a simple model of heredity – 5 parts:
Parents transmit “factors’ to offspring
Each individual receives 2 factors which code for the same trait
Not all factors are identical – alternative gene forms are called alleles
Alleles do not influence each other as alleles separate independently into gametes
The presence of an allele does not insure that its trait will be expressed