GENETICS -2A Gregor Mendel

E. Law’s of Heredity The Law of Segregation – Two alleles responsible for a trait separate when gametes are formed. a. Alleles then "recombined" at fertilization. b. Shown by a monohybrid cross (tests 1 trait). 2. The Law of independent Assortment – Alleles for different genes separate independently of one another in meiosis. a. Shown by a dihybrid cross (tests two traits).

E. Law’s of Heredity Mendelian Genetics 2/1/2017 3. Law of Dominance: In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. a. All the offspring will be heterozygous and express only the dominant trait. i. Example: RR x rr yields all Rr (round seeds)

f. Punnett Square 1. Punnett square – used to predict the outcome of a genetic cross. 2. Example: The two colors of flower (purple and white) – Alleles 3. Both parents have 2 different alleles – (Bb) Heterozygous

g. Monohybrid cross 1. Monohybrid: A cross in which only one trait is considered.

G. MonoHybrid Cross - Example Question: A pea plant that is heterozygous for round seeds is fertilized with a homozygous recessive wrinkled seed, what are the phenotypic ratios of the resulting offspring? Step 1A: Determine the letters and meaning of each letter (dominant and recessive traits). R = round r = wrinkled Step 1B: Determine the gametes of the parental genotypes. The word “heteroyzous” and “homozygous recessive” are the most important clues. Rr x rr

g. Monohybrid Cross - Example Step 3: Set up the 2x2 Punnett square, place one gamete set from the parent on the top, and the other on the side. Gamete 1 ___R_____ ___r_____ Gamete 2

g. Monohybrid Cross - Example Step 4: Complete the Punnett square by writing the genotypes of the offspring in each box and determine how many of each phenotype you have. RR = __0:4________ Rr = __2:4 = 1:2_____ rr = __ 2:4 = 1:2 __ Gamete 1 ___R_____ ___r_____ Gamete 2 Rr rr