Genetics I Genetic Diversity Gene Pool All the

Genetics

I. Genetic Diversity • Gene Pool - All the different genes found in a population (same species) • Variation is good for survival of a population!

II. Causes of Variation 1. Combinations of different parents 2. Independent Assortment: only one of the two genes from a parent goes into each sex cell 3. Cross-over during meiosis 4. Mutations

III. Alleles • Allele = Version of a gene Ex: red or brown hair • Expressed trait = the allele you “show” • Humans have 2 alleles (one from mom, one from dad) for each trait Example: Gene = flower color Alleles = purple or white

• Dominant Alleles – Allele that “masks” recessive alleles; always shows – Represented with a capital letter (A)

• Recessive Alleles – Allele that is “masked” by dominant alleles – Trait will only show if alleles from both parents are recessive – Represented with lower case letter (a)

• Gregor Mendel - Determined the Principle of Dominance: some alleles are dominant, some are recessive

IV. Predicting Genetics • Punnett Squares – used to determine probability of offspring traits • Each parent gives only one of their two alleles (genes) for a trait – but which one is RANDOM!

• Vocabulary: A. Genotype: the alleles (genes) a person has for a trait, represented by letters Ex: AA 1. Homozygous: two of the same alleles (AA, aa) 2. Heterozygous: two different alleles (Aa), also called a hybrid or carrier of a trait

B. Phenotype: the physical trait that is shown Ex: red hair

V. Punnett Squares • Each square shows a possible combination of the two parents’ genes Possible alleles from DAD Possible alleles from MOM

Bring top letter down, side letters over. What is the probability (%) that a child will be aa? What is the probability that a child will be Aa?

Practice: 1. Draw a Punnett Square 2. Cross a homozygous dominant father with a homozygous recessive mother 3. What is the probability (%) of a homozygous recessive child?

• Ratios: Used to say what the probability of one outcome is compared with another Ex: #tall vs. #short #tall : #short A. Genotypic Ratios 1. What are the possible genotypes? AA, Aa, aa 2. How many of each? 1 AA, 2 Aa, 1 aa 1: 2: 1 A = tall , a = short (25% chance AA, 50% chance Aa, 25% chance aa)

B. Phenotypic Ratios 1. What are the possible phenotypes? Tall, short 2. How many of each? 3 tall, 1 short therefore 3: 1 (75% chance tall, 25% chance short) A = tall , a = short

You try! 1. What is the probability (%) of these parents having a child that is AA? Aa? aa? 2. What is the probability of these parents having a child that is red? blue?

• Genotypic ratio Genotypes: Aa # of each: 4 Ratio: 4: 0 or 1: 0 • Phenotypic ratio Phenotypes: Red # of each: 4 Ratio: 1: 0

You try! • Genotypic ratio Genotypes: # of each: Ratio: • Phenotypic ratio Phenotypes: # of each: Ratio: T = dark green t = light green

Probability question. Purple ears (E) is dominant over green ears (e). 1. Cross a homozygous dominant father with a heterozygous mother. 2. What is the probability (%) they will have a child that is heterozygous for this trait? 3. What color will that heterozygous child have? **Start by making a Geno-Pheno KEY: geno’s pheno’s EE, Ee Purple ears ee Green ears