Genetics *transmission of traits – heredity *variation *genetics

Two main hypotheses on how traits were transmitted: *blending inheritance *particulate inheritance Gregor Johann Mendel The father of transmission genetics:

Mendel tracked heritable characters for three generations *P - parental generation *F 1 – first filial generation *F 2 – second filial generation -Example: X TallDwarf P F 1 – all Tall Tall F2F2

Mendel’s hypotheses (to explain his results) *genes and alleles 1. Alternative versions of genes (alleles) account for variation in inherited characters 2. For each character, an organism inherits two alleles, one from each parent

3. If two alleles differ, one is dominant, the other recessive X TallDwarf P: DD dd F 1 – all Tall Tall Dd 4. The two alleles for each character segregate (separate) during gamete production. Mendel’s Law of Segregation

Punnett Square predicts the results of a genetic cross between individuals of known genotype Ddd TallDwarf P: DD dd X Gamete formation: D *genotype *phenotype *Homozygous *Heterozygous

Mendel’s Law of Independent Assortment *What happened when he looked at two characters? If they segregate together:If they segregate independently:

Dihybrid cross- A genetic cross between two individuals involving two characters F1F1 All yellow, round GGWWggww Example: P1P1 yellow, roundgreen, wrinkled X Punnett square and the law of independent assortment: GW GW gw GgWw

F1F1 All yellow, round GgWw F1F1 All yellow, round GgWw X F2F2 9/16 yellow, round 3/16 yellow, wrinkled 3/16 green, round 1/16 green, wrinkled Punnett square and the law of independent assortment: GW Gw gW gw gW GW gw Gw 9:3:3:1 Phenotypic ratio; Genotypic ratio as follows: 1/16 GGWW, 2/16 GGWw, 2/16 GgWW, 4/16 GgWw 1/16 GGww, 2/16 Ggww 1/16 ggWw, 2/16 ggWw 1/16 ggww

Mendelian inheritance is based on probability Example- coin toss *1/2 chance landing heads *Each toss is an independent event *Coin toss, just like the distribution of alleles into gametes *The rule of multiplication – determines the chance that two or more independent events will occur together ½ x ½ = ¼