Dihybrid Cross & Beyond Dominant and Recessive Genetics January 6, 2011

Warmup In ginuea pigs, short hair (S) is dominant to long hair (s). Two short-haired ginuea pigs breed and one of the resulting offspring is long-haired. Draw the punnett square to represent this situation What are the genotypes of the parents?

Law of Independent Assortment Mendel wondered if alleles were “linked” together. He knew yellow seeds (Y) were dominant over green (y), and round seeds (R) were dominant over wrinkled (r). But… Are all yellow seeds were round? And all green seed were wrinkled?

Independent Assortment cont. So he crossed them- Got the F1 RRYY (round yellow) x rryy (wrinkled green) rryy RRYY    ry ry  RY  RrYy   RrYy

Independent Assortment cont Then he did the F2 He crossed the RrYy with RrYy Since the seeds in the generation no longer linked being yellow and round and green and wrinkled. Mendel now new that genes were independent of each other

Two laws from his observations Law of Segregation- when you make your gametes (sex cells), the copies of a gene separate. Ex. One of your sex cells may have an allele for brown hair and another gamete may have an allele for red hair Law of Independent Assortment- genes for different traits separate independently of one another Contributes to genetic variations observed in plants and animals

Beyond Dominant and Recessive Some alleles are not dominant or recessive and others are not controlled by just one gene! Incomplete Dominance Codominance Multiple Alleles Polygenic traits

Incomplete Dominance When one allele is not dominant over another. The heterozygous genotype produces a mix of the phenotypes Red and white flower producing PINK

Codominance When both alleles contribute to the phenotype Not mixed, but both present Example: Red cows x White cows  red and white spotted cows

Multiple Alleles When a gene has more than 2 possible alleles Although individuals can only have 2 there are more in nature Example – ABO Human Blood Type Example– Fur color in rabbits Single gene, 4 alleles

Blood Types

Polygenic trait When trait/phenotype is controlled by the interaction of more than 1 gene Example: Skin color in humans, high blood pressure and height Skin color- more than four different genes that control this trait

Polygenic traits- Skin Color

Homework Finish green “Genetic Basics” worksheet # 15, 16, 17, 20 Fill in front side of 11-3 notes sheet (read the section to complete) Quiz tomorrow!