11-2 Genetic Crosses

1. Genotype and Phenotype A. Genotype: the genetic make-up of an organism. The alleles that the organism inherits from the parents. 1.. Example – BB, Bb, bb, TT, Tt, tt B. Phenotype: the physical appearance of an organism as a result of its genotype.

C. Homozygous: when both alleles of a pair are alike. 1. example – BB or bb D. Heterozygous: when both alleles of a pair are different. 1. example – Bb E. Probability: the likelihood that a specific event will occur.

Probability Punnett Squares - are used to see the probability of different traits inherited by the offspring

2. Different Punnett Square crosses A. Homozygous Dom – Homozygous Dom = 100% Homozygous Dominate B. Homozygous Dom.- Homozygous Rec. = 100 % Heterozygous Dominate. C. Heterozygous – Homozygous Dom. = 50 % - 50% D. Heterozygous – Heterozygous = 25% Homo. Dom. , 50% Hetero. Dom., 25% homozygous rec.

A. Involves only one pair of contrasting traits. 2. Monohybrid crosses A. Involves only one pair of contrasting traits.

is crossed with a homozygous recessive individual. E. Testcrosses: an individual with unknown genotype is crossed with a homozygous recessive individual.

F. Incomplete Dominance- Occurs when two or more alleles influence the phenotype, resulting in neither factors takes on the dominant role and they compromise in a third trait.

Incomplete dominance

Complete dominance

H. Codominance: occurs when both alleles for a gene are expressed in a heterozygous offspring. 1. No trait is dominant and there is no blending of traits. Both traits are shown equally.

Co-dominance – Blood types

Chapter 11 Section 11:3 Dihybrids

3. Dihybrid Crosses A. Involves two pairs of contrasting traits

Constructing a Di-Hybrid cross 1. Dominant – Dominant 2. Dominant – Recessive 3. Recessive – Dominant 4. Recessive – Recessive