9 2 Genetic Crosses Genotype The genetic makeup

9 -2 Genetic Crosses Genotype: The genetic makeup of an organism, consisting of alleles inherited from parents. Ex: for purple flowers, genotype = PP or Pp for white flowers, genotype = pp Phenotype: The appearance of an organism as a result of its genotype. Ex: PP or Pp = purple flowers pp = white flowers Homozygous : both alleles of a pair are alike. Heterozygous : both alleles of a pair are different.

Probability: likelihood that a specific event will occur. Prob. = the # of times an event is expected to occur the # of opportunities for an event to occur Ex: In Mendel’s experiment: (for F 2 generation) yellow seed color appeared 6, 022 times green seed color appeared 2001 times total # of individuals was 8, 023 Do the math: Prob. Dominant: 6, 022 = 0. 75% 8, 023 Prob. Recessive: 2, 001 = 0. 25% 8, 023

Predicting results of monohybrid crosses Monohybrid cross: involves one pair of contrasting traits Ex 1: Homozygous x Homozygous

Ex 2: Homozygous x Heterozygous Ex 3: Heterozygous x Heterozygous

Ex 4: Testcross : unknown genotype crossed with homozygous recessive Ex 5: Incomplete Dominance : when 2 or more alleles influence the phenotype, resulting in an intermediate phenotype. (Ex: red & white = pink)

Ex 6: Codominance : When both alleles are expressed in a heterozygous offspring. No blending occurs!

Predicting Results of Dihybrid Crosses (involves 2 pairs of contrasting traits) • Homozygous x Homozygous • Heterozygous x Heterozygous coat color labrador

Section 9 -2 Review 1. Explain how you might determine the genotype of a purple-flowering pea? 2. What is the equation used to determine probability? In what ways can probability be expressed? 3. If you were to cross pink-flowering four o’clocks with white-flowering four o’clocks, what results would you expect? Provide a Punnett square to support our answer. 4. Explain how you would use a Punnett square to predict the probable outcome of a monohyrid cross. 5. Explain the difference between a monohybrid cross and a dihybrid cross. Give an example of each. 6. The offspring of 2 short-tailed cats have a 25% chance of having no tail, a 25% chance of having a long tail, and a 50% chance of having a short tail. Based on this information, what can you hypothesize about the genotypes of the parents?