Outline

1. Mendelian Inheritance

2. Outline • Blending Inheritance • Monohybrid Cross • Law of Segregation • Modern Genetics • Genotype vs. Phenotype • Punnett Square • Dihybrid Cross • Law of Independent Assortment • Human Genetic Disorders

3. Gregor Mendel

4. Gregor Mendel • Austrian monk • Studied science and mathematics at University of Vienna • Conducted breeding experiments with the garden pea Pisum sativum • Carefully gathered and documented mathematical data from his experiments • Formulated fundamental laws of heredity in early 1860s • Had no knowledge of cells or chromosomes • Did not have a microscope

5. Fruit and Flower of theGarden Pea

6. Mendel’s Monohybrid Crosses:An Example

7. Garden Pea TraitsStudied by Mendel

8. Blending Inheritance • Theories of inheritance in Mendel’s time: • Based on blending • Parents of contrasting appearance produce offspring of intermediate appearance • Mendel’s findings were in contrast with this • He formulated the particulate theory of inheritance • Inheritance involves reshuffling of genes from generation to generation

9. Mendel’s Monohybrid Crosses:An Example

10. One-Trait Inheritance • Mendel performed cross-breeding experiments • Used “true-breeding” (homozygous) plants • Chose varieties that differed in only one trait (monohybrid cross) • Performed reciprocal crosses • Parental generation = P • First filial generation offspring = F1 • Second filial generation offspring = F2 • Formulated the Law of Segregation

11. Law of Segregation • Each individual has a pair of factors (alleles) for each trait • The factors (alleles) segregate (separate) during gamete (sperm & egg) formation • Each gamete contains only one factor (allele) from each pair • Fertilization gives the offspring two factors for each trait

12. Modern Genetics View • Each trait in a pea plant is controlled by two alleles (alternate forms of a gene) • Dominant allele (capital letter) masks the expression of the recessive allele (lower-case) • Alleles occur on a homologous pair of chromosomes at a particular gene locus • Homozygous = identical alleles • Heterozygous = different alleles

13. Homologous Chromosomes

14. Genotype Versus Phenotype • Genotype • Refers to the two alleles an individual has for a specific trait • If identical, genotype is homozygous • If different, genotype is heterozygous • Phenotype • Refers to the physical appearance of the individual

15. Punnett Square • Table listing all possible genotypes resulting from a cross • All possible sperm genotypes are lined up on one side • All possible egg genotypes are lined up on the other side • Every possible zygote genotypes are placed within the squares

16. Punnett Square ShowingEarlobe Inheritance Patterns

17. MONOHYBRID CROSS Cross a heterozygous tall plant with a heterozygous tall plant (use T = tall and t = short) Determine expected genotype and phenotype ratios. Try this one

18. Monohybrid Testcross • Individuals with recessive phenotype always have the homozygous recessive genotype • However, Individuals with dominant phenotype have indeterminate genotype • May be homozygous dominant, or • Heterozygous • Test cross determines genotype of individual having dominant phenotype

19. One-Trait Test CrossUnknown is Heterozygous

20. One-Trait Test CrossUnknown is Homozygous Dominant

21. IS MY DOG A PURE BREED? • Do a test cross: G = golden retriever • g = other

22. Not so much!

23. Two-Trait Inheritance • Dihybrid cross uses true-breeding plants differing in two traits • Observed phenotypes among F2 plants • Formulated Law of Independent Assortment • The pair of factors for one trait segregate independently of the factors for other traits • All possible combinations of factors can occur in the gametes

24. Try Mendel’s Classic Dihybrid Cross • Cross two heterozygous tall, heterozygous green pod producing plants. Use a punnett square to show expected offspring and complete a phenotype ratio. • Key: • T = tall G = green pods • t = short g = yellow pods

25. Two-Trait (Dihybrid) Cross

26. Hartford’s example

27. Rat Answers

28. Two-Trait Test Cross

32. Rules of Probability *segregation and independent assortment of alleles during meiosis and fertilization are random events *if we know genotype of parents we can predict the EXPECTED genotypes of offspring using rules of probability SOLVING GENETICS PROBLEMS

33. Scale range: 0-1 The probability of all possible outcomes for an event must add up to 1 Probability Scale

34. EVENT PROBABILITY *tossing heads w/normal coin………………1/2 *tossing tails w/normal coin………………1/2 1 Common Examples

35. Probability of rolling 3 on a six-sided die? 1/6 Probability of rolling a number other than 3? 5/6 Try a common one

36. Random events are independent of one another! If a couple has 6 sons and tries for the little girl: there is still a ½ chance of getting their wish. Regardless of the past events!

37. LAWS OF PROBABILITY* Rule of multiplication*Rule of addition

39. Q: In a Mendelian cross between two heterozygous pea plants (Tt), what is the probability that the offspring will be homozygous recessive? A: egg w/ t = ½ sperm w/ t = ½ overall probability that two will unite is ½ x ½ = ¼ Ex 3 - monohybrid

40. Q: For YyRr x YyRr, what is the probability of an F2 plant having genotype YYRR? A: prob. of egg w/ YR = ½ x ½ = ¼ prob. of sperm w/ YR = ½ x ½ = ¼ Overall prob. for offspring: ¼ x ¼ = 1/16 Ex 4. Dihybrid cross

41. Q: What is the probability that a trihybrid cross between two organisms with genotypes AaBbCc and AaBbCc produce an AABBCc offspring? A: Look at each allele pair separately Aa x Aa: prob. of AA = ¼ Bb x Bb: prob. of BB = ¼ Cc x Cc: prob. of Cc = ½ Overall that this will occur simultaneously: ¼ x ¼ x ½ = 1/32 Ex. 5 Trihybrid

42. The probability of an event that can occur in two or more independent ways is the sum of the separate probabilities of the different ways. Think heterozygotes! Rule of Addition

43. ¼ + ¼ = 1/2

44. Q: In a Mendelian cross between pea plants that are heterozygous (Pp), what is the probability of the offspring being heterozygous? A: there are two different ways for this to occur- 1) sperm gives P and egg gives p OR 2) egg gives P and sperm gives p Ex. 2: monohybrids

45. So… sperm gives P and egg gives p ½ X ½ = ¼ 2) egg gives P and sperm gives p ½ X ½ = ¼ OVERALL PROB. of way 1 or way 2 ¼ + ¼ = ½

46. EX 3 - Dihybrid What is the probability that two parents heterozygous for both height and flower color will produce HETEROZYGOUS tall offspring with purple flowers?

47. Q: What is the probability that a trihybrid cross between two organisms with genotypes AaBbCc and AaBbCc produce an aabbcc offspring? A: Look at each allele pair separately Aa x Aa: prob. of aa = ¼ Bb x Bb: prob. of bb = ¼ Cc x Cc: prob. of cc = ¼ Overall that this will occur simultaneously: ¼ x ¼ x ¼ = 1/64 Ex 4 Trihybrid

48. Q: PpYyRr x Ppyyrr What is the chance that the offspring will show at least two recessive phenotypes out of the three traits? A: break down the possibilities of all the genotypes that are homozygous recessive for at least two traits: ppyyRr, ppYyrr, Ppyyrr, PPyyrr, and ppyyrr Ex. 5 Trihybrid

49. PpYyRr x Ppyyrr ppyyRr ¼ x ½ x ½ = 1/16 ppYyrr ¼ x ½ x ½ = 1/16 Ppyyrr ½ x ½ x ½ = 2/16 PPyyrr ¼ x ½ x ½ = 1/16 ppyyrr ¼ x ½ x ½ = 1/16 6/16 or 3/8 chance of an offspring showing at least 2 of the recessive traits

50. CHAPTER 11 – autosomal disorders CHAPTER 12 – sex-linked and gene-linked and trisomy/monosomy ANALYZING GENETIC DISORDERS