Applying Mendels Principles Learning Objectives Explain how geneticists

Applying Mendel’s Principles

Learning Objectives § Explain how geneticists use the principles of probability to make Punnett squares. § Explain the principle of independent assortment. § Explain how Mendel’s principles apply to all organisms.

Determining Probability: the likelihood an event will occur • Probability of either outcome: 50% or 1/2 • Three coin tosses? 1/2 × 1/2 = 1/8 • Each flip is an independent event.

Using Segregation to Predict Outcomes Probability of a gamete receiving a T? 50%, or 1/2 Probability of gamete receiving a t? 50%, or 1/2 Probability of tall offspring is Probability of short offspring is 3/4 1/4 . .

Genotype and Phenotype Genotype: genetic makeup Phenotype: physical traits Two organisms may share the same phenotype but have different genotypes.

Heterozygous and Homozygous: has two identical alleles for a gene Heterozygous: has two different alleles for a gene Which are: homozygous? 1, 4 heterozygous? 2, 3 1 2 3 4

Making a Punnett Square A cross of ospreys: beak size (B, b) Possible gametes Gametes for a parent along one side Combine gamete genotypes

Making a Punnett Square: Two Factors A cross of pea plants: size (T, t) and pod color (G, g) All possible gametes All gametes for a parent along one side Combine gamete genotypes

The Two-Factor Cross: F 1

The Two-Factor Cross: F 2 Independent assortment: Genes for different traits can segregate independently during gamete formation. 9: 3: 3: 1 ratio of phenotypes

Summary of Mendel’s Principles, Part I Inheritance is determined by units called genes passed from parents to offspring. , which are Where more than one form of a gene for a single trait exists, some alleles may be dominant and others recessive.

Summary Mendel’s Principles, Part II • Each adult has two copies of each gene—one from each parent. These genes segregate from each other when gametes are formed. • Alleles for different genes usually segregate independently of each other.