Patterns of Inheritance – Mendelian Genetics

1. Patterns of Inheritance – Mendelian Genetics

2. Genes • Location of a gene on a chromosome is called its locus • Homologous chromosomes

3. What are alleles?

4. Homozygous Alleles vs. Heterozygous Alleles

5. Who Was Gregor Mendel? nitro.biosci.arizona.edu

6. Secrets of Mendel’s Success

7. Self-fertilization • Pea flowers can self-fertilize • Pollen from male structures transfers to eggs in female structures

8. True-breeding • Plants homozygous for a characteristic are true-breeding

9. Cross-fertilization • Mendel was able to mate two different plants by hand (cross-fertilization) • Female parts (carpels) were dusted with pollen from other selected plants

10. Secrets of Mendel’s Success • Mendel experimental design was simple and methodical • Chose a good organism to study • Studied characteristics that have unmistakably different forms (like purple versus white) • Studied one trait (characteristic) at a time

11. Genetic Cross • The mating of pollen and eggs (from same or different parents)

12. Genetic Cross • Parents used in a cross are part of the parental generation(known as P) • Offspring of the P generation are members of the first filial generation(F1) • Offspring of the F1 generation are members of the F2 generation, etc.

15. Alleles • Every cell in a pea plant carries 2 alleles per characteristic (either the same or different)

16. Genotype vs Phenotype • Genotype • Particular combination of the 2 alleles carried by an individual • (e.g. PP, Pp, or pp) • Phenotype • Physical expression of the genotype • (e.g. purple or white flowers)

17. Dominant and Recessive Alleles

18. How Meiosis Separates Genes • 2 alleles for a characteristic separate during gamete formation (meiosis) • Homologous chromosomes separate in meiosis anaphase I • During meiosis anaphase II, each gamete receives one of each pair of homologous chromosomes and thus one of the two alleles per characteristic

19. How Meiosis Separates Genes • Separation of alleles in meiosis is known as Mendel’s Law of Segregation

24. Genetic Bookkeeping • Punnett Square Method predicts offspring genotypes from combinations of parental gametes

25. Genetic Bookkeeping • From the sums of all the different kinds of offspring genotypes, create a genotypic ratio • ¼ PP, ½ Pp, ¼ pp is in the ratio 1PP: 2Pp: 1pp • Based on dominant and recessive rules, determine the phenotypic ratio • A genotypic ratio of 1PP: 2Pp: 1pp yields 3 purple flower plants: 1 white flower plant

26. The Test Cross

27. Traits Inherited Independently • Mendel performed genetic crosses in which he followed the inheritance of two traits at the same time

28. Traits Inherited Independently • Seed color (yellow vs. green peas) and seed shape (smooth vs. wrinkled peas) were characteristics studied • Allele symbols were assigned: • Y = yellow (dominant), y = green (recessive) • S = smooth (dominant), s = wrinkled (recessive)

29. Traits Inherited Independently • 2 trait cross was between two true breeding varieties for each characteristic • P: SSYY x ssyy

30. Traits Inherited Independently • Mendel then allowed the F1 offspring to self fertilize: SsYy x SsYy

31. Mendel’s Genius Went Unrecognized