Inheritance

1. crosstopix.blogspot.com Inheritance LECTURE #13

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. Scientific method • Materials • Garden pea (Pisumsativum) • Tweezers and a paintbrush • Methods • Crossing various “parent” plants • Observing traits of the offspring • Results • The set of principles that govern inheritance

4. Black box • Inferences made by Mendel… #1. The basic units of inheritance are material elements. • Genes = Elements of DNA located on chromosomes

5. Black box • Inferences made by Mendel… #2. These elements come in pairs. • Homologous chromosomes = Similar in size and content, but contain different genes.(one from mom, one from dad) • Diploid organisms have 2 copies

6. Black box • Inferences made by Mendel… #3. Pairs separate during the formation of gametes. • Meiosis I = Separation and independent assortment of homologous chromosomes. • Each sperm or egg only gets one copy of each gene. • Haploid gametes

7. Black box • Inferences made by Mendel… #4. Elements retain character through generations. • Chromosomes copied during meiosis and getpassed on unchanged into next generation.

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

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

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

11. hobbyandblog.com

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

14. The Experiments • Pea plants normally self-pollinate • Mendel was able to force pea plants to cross-pollinate

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

16. 7 different characters. 2 traits for each. Traits are either dominant or recessive.

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

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

19. 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

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

21. 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

23. What Mendel learned… • No “blending” of characteristics • Discrete elements are being transmitted • Green seeds absent from F1, but reappear in F2 so they must have been present in F1 generation too. • Traits caused by pairs of elements • Paired genes exist on homologous chromosomes • Allele = different form of a gene (yellow allele, green allele)

24. Dominant vs. Recessive • Capital letters designate dominant alleles • Lower case letters designate recessive Y y

25. Dominant vs. Recessive • A true-breeding plant would have two dominant alleles for that trait. • Homozygous dominant = two dominant alleles Y Y Genotype  YY Phenotype  yellow seeds Gametes produced  only have Y allele

26. Dominant vs. Recessive • A true-breeding plant would have two recessive alleles for that trait. • Homozygous recessive= two recessive alleles y y Genotype  yy Phenotype  green seeds Gametes produced  only have y allele

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

28. Mendel’s Law of Segregation • Individuals possess two alleles for each gene • These alleles separate during gamete production (meiosis) • Since alleles reside on chromosomes, alleles separate when homologous chromosomes separate during meiosisI.

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

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

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

34. Activity • Worksheet Part I

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

36. Dihybrid cross • P: smooth yellow x wrinkled green • Genotypes: SSYY x ssyy • Gametes: SY and sy • F1generation: All SsYy • All smooth and yellow • All heterozygous for both traits

37. Dihybrid cross • F1: double heterozygotes self-pollinate • Genotypes: SsYy x SsYy • Gametes: SY , Sy , sY, and sy • F2generation • Four different phenotypes

38. 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

39. Gametes will be composed of some arrangement of SsYy

40. 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

41. Activity • Worksheet Part II

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

43. 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

44. Blood Type • Six allele combinations produce four blood types Blood typeGenotypeMolecules present Type A AA or AO “A” molecule Type B BB or BO “B” molecule Type AB AB “A” and “B” Type O OO neither is present

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

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

48. Genes and the environment • Environmental factors also influence traits • External factors affect phenotypic expression • Smoking  development of lung cancer • Soil pH color of hydrangeas

49. Writing response • At the beginning of this chapter of the book, a newspaper article states that blonde hair is “so recessive” that it will eventually disappear from the population. • Explain why this is so unlikely. • Explain why the phrase “so recessive”doesn’t make any sense.