Mendel's Discoveries on Inheritance of Traits in Pea Plants

1. Chapter 14 Mendel and the Gene Idea

2. 14.1 • Blending vs. particulate ideas • Anecdotally many thought children inherited “_______” of their parents • Mendel showed that some traits are _____

3. Vocab • Character- varieties with distinct heritable features (such as flower color) • Trait- character variants (such as purple or white flowers) • **sometimes used interchangeably**

4. Why Peas? • . • . • .

5. Fig. 14-2a TECHNIQUE 1 2 Parental generation (P) Stamens Carpel 3 4

6. Mendel chose to track only those characters that varied in an either-or manner • What does that mean? • He also used varieties that were true-breeding

7. Vocab!! • In a typical experiment, Mendel mated two contrasting, true-breeding varieties, a process called hybridization

8. Fig. 14-3-3 EXPERIMENT P Generation (true-breeding parents)  Purple flowers White flowers F1 Generation (hybrids) All plants had purple flowers F2 Generation 224 white-flowered plants 705 purple-flowered plants

9. What Mendel called a “heritable factor” is what we now call a gene • Mendel observed the same pattern of inheritance in six other pea plant characters, each represented by two traits

10. Reflect • What did Mendel discover? • What’s the typical ratio for F2 generation?

11. Law of Segregation 1. Alternative versions of genes account for variations in inherited characters • Ex.

12. 2 • Organisms inherits two alleles for every gene, one from each parent • Those two alleles: • May be • May be

13. 3 • If the two alleles at a locus differ, then one (the dominant allele) determines the organism’s appearance, and the other (the recessive allele) has no noticeable effect on appearance • In the flower-color example, the F1 plants had purple flowers because the allele for that trait is dominant

14. 4. Law of Segregation • The two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes • Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism • Meiosis anyone??

15. Vocab • Alleles- alternative versions of a gene • Locus- location on a specific chromosome Each gene resides at a specific locus • Dominant • Recessive

16. Fig. 14-4 Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers

17. Punnett square- a diagram for predicting the results of a genetic cross between individuals of known genetic makeup

18. homozygous – having two _______alleles for a gene • heterozygous having two ________alleles for a gene • Not ___________

19. Genotype v Phenotype • Because of the different effects of dominant and recessive alleles, an organism’s traits do not always reveal its genetic composition • Genotype- genetic makeup • . • . • . • Phenotype- physical appearance/expression of the gene

20. Fig. 14-6 Phenotype Genotype PP Purple 1 (homozygous) Pp 3 Purple (heterozygous) 2 Pp Purple (heterozygous) pp White 1 1 (homozygous) Ratio 3:1 Ratio 1:2:1

21. Testcross • How can we tell the genotype of an individual with the dominant phenotype? • testcross:

22. Fig. 14-7 TECHNIQUE  Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp Predictions If PP If Pp or Sperm Sperm p p p p P P Pp Pp Pp Pp Eggs Eggs P p pp Pp pp Pp RESULTS or All offspring purple 1/2 offspring purple and 1/2 offspring white

23. Monohybrid • A cross between heterozygotes is called a monohybrid cross

24. Dihybrid • dihybrids - heterozygous for two genes • Mendel used dihybrid crosses to figure out the law of independent assortment

25. Fig. 14-8 EXPERIMENT YYRR yyrr P Generation Gametes yr YR  F1 Generation YyRr Hypothesis of dependent assortment Hypothesis of independent assortment Predictions Sperm or Predicted offspring of F2 generation 1/4 1/4 1/4 yr 1/4 YR yR Yr Sperm YR yr 1/2 1/2 1/4 YR YYRr YYRR YyRR YyRr 1/2 YR YyRr YYRR 1/4 Yr Eggs YYRr YYrr Yyrr YyRr Eggs 1/2 yr YyRr yyrr 1/4 yR YyRR YyRr yyRR yyRr 3/4 1/4 1/4 yr Phenotypic ratio 3:1 Yyrr yyRr YyRr yyrr 3/16 1/16 9/16 3/16 Phenotypic ratio 9:3:3:1 RESULTS Phenotypic ratio approximately 9:3:3:1 315 108 101 32

26. Law of independent assortment • Each pair of alleles segregates independently of each other pair of alleles during gamete formation • Ex. • This law applies only to genes on different, nonhomologous chromosomes

27. 14.2 • When tossing a coin, the outcome of one toss has no impact on the outcome of the next toss • In the same way, the alleles of one gene segregate into gametes independently of another gene’s alleles

28. The multiplication rule states that the probability that two or more independent events will occur together is the product of their individual probabilities

29. Fig. 14-9 Rr Rr  Segregation of alleles into sperm Segregation of alleles into eggs Sperm 1/2 1/2 R r R R R 1/2 r R 1/4 1/4 Eggs r r r R 1/2 r 1/4 1/4

30. The rule of addition states that the probability that any one of two or more exclusive events will occur is calculated by adding together their individual probabilities

31. The rule of addition can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous rather than homozygous

32. Fig. 14-UN1

33. 14.3 Inheritance patterns are often more complex than predicted by simple Mendelian genetics • Many heritable characters are not determined by only one gene with two alleles • However, the basic principles of segregation and independent assortment apply even to more complex patterns of inheritance

34. Non-Mendelian situations include • When alleles are not ______________ • When a gene has more than ___________ • When a gene produces _________________

35. Degrees of Dominance • Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical • Incomplete dominance, the phenotype of F1hybrids • Codominance-two dominant alleles affect the phenotype ________________________

36. Fig. 14-10-3 P Generation Red White CRCR CWCW CR CW Gametes Pink F1 Generation CRCW 1/2 1/2 CR CW Gametes Sperm 1/2 1/2 CR CW F2 Generation 1/2 CR CRCW CRCR Eggs 1/2 CW CRCW CWCW

37. Tay-Sachs • Tay-Sachsdisease is fatal; a dysfunctional enzyme causes an accumulation of lipids in the brain • At the organismal level, the allele is recessive • At the biochemical level, the phenotype (i.e., the enzyme activity level) is incompletely dominant • At the molecular level, the alleles are codominant

38. Dominance is NOT PREdominance! • Dominant alleles are not necessarily more common in populations than recessive alleles • For example, one baby out of 400 in the United States is born with extra fingers or toes

39. Multiple Alleles • Most genes exist in populations in more than two allelic forms • For example, the four phenotypes of the ABO blood group in humans are determined by three alleles for the enzyme (I) that attaches A or B carbohydrates to red blood cells: IA, IB, and i. • The enzyme encoded by the IA allele adds the A carbohydrate, whereas the enzyme encoded by the IB allele adds the B carbohydrate; the enzyme encoded by the i allele adds neither

40. Fig. 14-11 Carbohydrate Allele Phenotype (blood group) Red blood cell appearance Genotype IA A B IB i none (a) The three alleles for the ABO blood groups and their associated carbohydrates IAIA or IA i A B IBIB or IB i AB IAIB ii O (b) Blood group genotypes and phenotypes

41. Pleiotropy • pleiotropy– genes that have multiple phenotypic effects • Ex. cystic fibrosis and sickle-cell disease have MULTIPLE SYMPTOMS

42. Epistasis • Epistasis-a gene at one locus alters the phenotypic expression of a gene at a second locus • Ex.

43. Fig. 14-12  BbCc BbCc Sperm 1/4 1/4 1/4 1/4 BC bC Bc bc Eggs 1/4 BC BBCc BBCC BbCC BbCc 1/4 bC bbCC bbCc BbCC BbCc 1/4 Bc BBcc Bbcc BBCc BbCc 1/4 bc BbCc bbCc Bbcc bbcc : 4 9 : 3

44. Polygenic Inheritance • Quantitative characters are those that vary in the population along a continuum • Indicate polygenic inheritance(an additive effect) of two or more genes on a single phenotype • Ex.

45. Fig. 14-13  AaBbCc AaBbCc Sperm 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 1/8 Eggs 1/8 1/8 1/8 1/8 Phenotypes: 1/64 6/64 15/64 20/64 15/64 1/64 6/64 Number of dark-skin alleles: 2 6 0 3 4 5 1

46. Nature and Nurture: The Environmental Impact on Phenotype • For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity • Sea Turtles? • Obesity/Heart Disease/ Diabetes

47. 14.4 Human Mendelian Traits • Humans are not good subjects for genetic research • . • . • . • However, basic Mendelian genetics endures as the foundation of human genetics

48. Pedigree • A family tree that describes the interrelationships of parents and children across generations

49. Fig. 14-15b 1st generation (grandparents) Ww Ww ww ww 2nd generation (parents, aunts, and uncles) Ww Ww ww ww Ww ww 3rd generation (two sisters) WW ww or Ww Widow’s peak No widow’s peak (a) Is a widow’s peak a dominant or recessive trait?

50. Fig. 14-15c 1st generation (grandparents) Ff Ff ff Ff 2nd generation (parents, aunts, and uncles) Ff Ff FF or ff ff Ff ff 3rd generation (two sisters) ff FF or Ff Attached earlobe Free earlobe (b) Is an attached earlobe a dominant or recessive trait?