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.

13. FIGURE 12-4 Cross of white and purple pea flowers

14. FIGURE 12-5 Cross of F1 purple pea flowers

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

16. Genotype vs Phenotype Genotype Phenotype
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

20. FIGURE 12-6 Chromosomes in the gametes of a homozygous parent

21. FIGURE 12-7 Chromosomes in the gametes of a heterozygous parent

22. FIGURE 12-8 Gametes from peas homozygous for purple and white flowers

23. FIGURE 12-9 Combinations of gametes that produce F1 offspring flowers

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
FIGURE 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