Inheritance OR: Why did Dumbo have such big ears?

1. crosstopix.blogspot.com Inheritance OR: Why did Dumbo have such big ears? LECTURE #13 Winter 2011

2. Inheritance • Concept of inheritance is ancient and universal. • How traits are transmitted was a mystery… • Gregor Mendel, mid-1800sAustrian naturalist and monk • “Black Box” of genetics

3. Black box • Inferences made by Mendel… #1. The basic units of inheritance are material elements. #2. These elements come in pairs. #3. Pairs separate during the formation of gametes. • Meiosis I #4. Elements retain character through generations.

4. Mendel’s peas liseed.org gstuff.co.nz

5. Garden pea biology • Cross-pollinate OR • Self-pollinate • Each pollen grain unique • Each egg in ovary unique = unique progeny monstergirlee.blogspot.com

6. Fertilization in plants Anthers contain pollen grains Ovary contains the eggs

7. Peas in a pod • Each pea contains an embryo • Each embryo is a separate individual… … from a separate fertilization event … with different traits • The peas in a pod are not identical. blog.locallectual.com

9. The Experiments • Mendel “forced” hispea plants to cross-pollinate

10. CROSS POLLINATING 1. Clip anthers off mother plant. 2. Gather pollen from father plant. 3. Rub father plant pollen on mother plant’s stigma.

11. 7 different characters. 2 traits for each. Traits are either dominant or recessive.

12. Genotype vs. Phenotype • Genotype = all the genes belonging to a single individual • Phenotype= the • physical appearance of an individual. • Genotype + Environment anthro.palomar.edu

13. Terminology • P generation = parent generation • F1 generation = first filial; offspring from P • F2 generation = second filial; offspring from F1

14. The Experiments • “True breeding” plants • Example: All pea plants from yellow seeds also have only yellow-seeded F1 and F2 progeny. • Mendel only used these for P generation

15. Results of cross • True-breeding P generation (yellow x green) • F1 generation is ALL yellow • No green seeds, no “blending” of inheritance 

16. Results of cross • F1 generation planted and allowed to “self” • F2 generation • 6,022 yellow seeds • 2,001 green seeds • ¾ are yellow, ¼ are green • 3:1 ratio • Yellow:green • Dominant:recessive

17. Dominant vs. Recessive • Dominant: Always visible • Recessive: Only visible if 2 copies

19. Dominant Alleles • True-breeding plant has 2 identical alleles for that trait. • Homozygous dominant = two dominant alleles Y Y Genotype  YY Phenotype  yellow seeds Gametes produced  only have Y allele

20. Recessive Alleles • True-breeding plant has 2 identical alleles for that trait. • Homozygous recessive= two recessive alleles y y Genotype  yy Phenotype  green seeds Gametes produced  only have y allele

21. Dominant vs. Recessive • Heterozygous = two different alleles Y y Genotype  Yy Phenotype  yellow seeds Gametes produced  one Y allele and one y allele

22. Mendel’s Law of Segregation • Individuals possess two alleles for each gene • These alleles separate during gamete production (meiosis) • Alleles separate when homologous chromosomes separate (Meiosis I)

23. Ratios of different genotypes and phenotypes are best illustrated using a Punnett square

25. The green phenotype couldn’t be expressed in the F1 generation because the dominant allele (Y) was present.

27. A pattern to progeny Genotypic ratio 1:2:1 YY : Yy: yy Phenotypic ratio 3:1 dominant : recessive

28. Activity • Worksheet Part I

29. Dihybrid crosses • Dihybrid cross = involve crossing 2 characters. • Monohybrid cross • Yellow seeds x green seeds • Smooth seeds x wrinkled seeds • Dihybrid cross • Smooth yellow x wrinkled green

30. Dihybrid cross • P: smooth yellow x wrinkled green • Genotypes: SSYY x ssyy • Gametes: SY and sy • F1 generation: All SsYy • All smooth and yellow • All heterozygous for both traits

31. Dihybrid cross • F1: double heterozygotes self-pollinate • Genotypes: SsYy x SsYy • Gametes: SY , Sy , sY, and sy • F2 generation • Four different phenotypes

32. Dihybrid cross • F2 generation • 315 smooth yellow • 101 wrinkled yellow • 108 smooth green • 32 wrinkled green • 9:3:3:1 phenotypic ratio • 3:1 phenotypic ratio still preserved for each character! • yellow:green • smooth:wrinkled • The transmission of one trait did not affect the other

33. Gametes will be composed of some arrangement of SsYy

34. Mendel’s Law of Independent Assortment • During gamete formation, gene pairs assort independent of one another • The transmission of one character does not influence the transmission of another character • Independent assortment in Meiosis I

35. Activity • Worksheet Part II

36. Multiple alleles, genes • Mendel’s peas • Single gene, 2 alleles for each • 2 potential phenotypes • Reality (most characters) • Multiple genes involved • More than 2 alleles for each gene (2-302 alleles)

37. Human blood type • Types: A, B, AB, and O • Determined by types of glycoproteinson the surface of red blood cells • Single gene on chromosome 9 • Three alleles for glycoprotein • “A” allele  A molecule • “B” allele  B molecule • “o” allele  no molecule

38. Codominance • Six allele combinations produce four blood types Blood typeGenotypeGlycoproteins present Type A AA or Ao “A” molecule Type B BB or Bo “B” molecule Type AB AB “A” and “B” Type ooo neither is present

39. A and B display dominance over the recessive O allele. But A and B are both expressed when together = codominant.

40. Incomplete dominance Genotypes: WW CW CC ultimatehorsesite.com totaleclipsefarms.com statesymbolsusa.org

41. Polygenic inheritance • Several genes contribute additive effects to a character. • Not either/or characters (yellow vs. green) • Human height, skin color, etc. • Length of an ear of corn • Amount of milk production in a cow

43. Genes and the environment • Environmental factors also greatly influence traits • Smoking  development of lung cancer • Soil pH  color of hydrangeas • Temperature  Siamese cat coloring