Genetics & Heredity

1. Genetics & Heredity Mendel and His Peas

3. Gregor Mendel • Heredity – the passing of traits from parents to offspring • Gregor Mendel – “father of genetics” • Austrian monk • performed experiments on peas to help answer questions about genetics • Genetics – the study of how traits are passed from parents to offspring

4. Mendel’s First Pea Experiment • Cross-pollinated • Purple flowers x purple flowers = all purple flowers • White flowers x white flowers = all white flowers • Purple flowers x white flowers = all purple flowers

5. Mendel’s Second Pea Experiment • Self-pollinated the hybrid flowers from the first generation (the offspring that were a result of the purple flowers x white flowers) • Results: • some offspring were purple and some were white

6. Mendel’s Conclusions • Dominant and Recessive • Dominant Trait • a genetic factor that blocks another genetic factor (ex. purple color (P)) • Recessive Trait • a genetic factor that is blocked by the presence of a dominant factor (ex. white color (p)) • recessive trait is observed only when two recessive genetic factors are present in offspring (pp)

7. Ratios • A comparison of two numbers or quantities by division • The ratio of purple to white flowers in Mendel’s second experiment is 3 to 1 or 3:1 or 3/1 • Try it: • There are 14 girls and 7 boys in a classroom. What is the ratio of girls to boys? Boys to girls?

8. Inheritance

9. Genes & Alleles • Gene– a section on a chromosome that has genetic information for one trait • ex. flower color • Allele – the different forms of a gene • ex. purple, white

10. Genotype & Phenotype • Phenotype – how a trait appears, or is expressed • ex. purple flowers, blue eyes, red hair • Genotype – the two alleles that control the phenotype of a trait • expressed as letters • uppercase for dominant • lowercase for recessive

11. Homozygous and Heterozygous • Homozygous – when the two alleles of a gene are the same • homozygous dominant - purple flowers (PP) • homozygous recessive - white flowers (pp) • Heterozygous – when the two alleles of a gene are different • ex. purple flowers (Pp)

12. Punnett Squares • Punnett square – a model used to predict possible genotypes and phenotypes of offspring • expressed as a probability (percent chance) • Phenotype: • Green = 75% • Yellow= 25% • Genotype: • GG = 25% • Gg = 50% • Gg = 25%

13. Punnett Square Examples

14. Draw a Punnett square for the following breeding pair of frogs: Gg x Gg If green skin (G) is dominant to yellow skin (g), what is the probability of the offspring being green?

15. Try Some Punnett Squares: • Brown eyes (BB) x Blue eyes (bb) • Freckles (Ff) x no freckles (ff)

16. Pedigree • Pedigree – a chart that shows phenotypes of genetically related family members • Symbols:

17. Pedigree Example

18. Patterns of Inheritance

19. Types of Dominance • Incomplete Dominance – when the phenotype of an offspring is a combination of the parents’ phenotype • ex. white flower x red flower = pink flower • Codominance – when two alleles can be observed in a phenotype • ex. white cow x black cow = spotted cow

20. Other Patterns of Inheritance • Multiple Alleles • genes with more than two alleles • ex. blood type (A, B, AB, O) • Sex-linked Traits • alleles found on the sex chromosomes (X, Y) • Polygenic Inheritance • when multiple genes determine the phenotype of a trait • ex. height