CHAPTER 11 MENDEL & HEREDITY

1. CHAPTER 11MENDEL & HEREDITY SC STANDARD B 4: The student will understand the molecular basis of heredity.

2. Essential Question • How does segregation of alleles contribute to genetic variation?

3. Origins of Hereditary Science • Mendel” Breeding Experiments • Genetics: is the science of heredity &the mechanism by which traits are passed from parents to offspring • Mendel • born in Austrian Empire (today Czech Republic) in 1822 • Studied physics & mathematics @ University of Vienna • Joined monastery in 1843 where he was put in charge of the gardens

4. Mendel’s Experiments • Mendel spent 2 years preparing his control plants to insure they were true breeders • describes organisms that are homozygous for a specific trait so always produce offspring that have the same phenotype for that trait

5. Mendel’s Experiments

6. Mendel’s Experiments • crossed true breeding, purple blossomed pea plants with true breeding, white blossomed pea plants and all the offspring had purple flowers • Then let the offspring self-pollinate and some of the plants in that generation had purple flowers & some had white

7. male parts were removed from 1st flower pollen taken from male parts of 2nd flower pollen from 2nd brushed onto female parts of 1st flower Mendel’s Experiments

8. Mendel’s Experiments Vocabulary: - character: a recognizable inherited feature or characteristic of an individual - trait: one of two or more possible forms of a character ~ phenotype: physical characteristics ~ genotype: genetic makeup , what alleles an organism has

9. Mendel’s Experiments Vocabulary: - hybrid: the offspring of a cross between parents that have contrasting traits - generation: the entire group of offspring produced by a given group of parents

10. Mendel’s Experiments • 3 reasons why the garden pea plant was good choice: • Several characters appear in contrasting forms • These flowers can self-pollinate because each flower has both male & female parts • Plant is easy to grow • Matures quickly • Needs little care • Produces many offspring

11. Mendel’s Experiments • Monohybrid Cross

12. Mendel’s Experiments • Monohybrid Cross: 3 Steps • Produced a true-breeding parent generation (P generation) • Produced 1st filial generation ( F 1 generation) • Produced 2nd filial generation ( F 2 generation)

13. True breeding purple True breeding white Mendel’s Experiments

14. Step 2: cross pollinated parents F 1 generation all purple Self-pollinated F 2 generation 3 : 1 purple to white Mendel’s Experiments

15. Mendel’s Experiments • Mendel repeated these experiments with 7 different traits in pea plants: For each of the 7 characters he found a similar 3 : 1 ratio of contrasting traits in the F 2 generation

16. Mendel’s Experiments

17. Mendel’s Experiments • Ratios in Mendel’s Results • F 1 generation expressed the same trait for any of the 7 characteristics he studied • When F 1 plants allowed to self-pollinate he always saw a 3 : 1 ratio of contrasting traits

18. Mendel’s Theory • Explains simple patterns of inheritance • 2 of several versions of a gene combine & result in 1 of several possible traits • Allele: one of two or more alternative forms of a gene each leading to a unique trait

19. Dominant:describes an allele that is fully expressed whenever the allele is present Recessive:describes an allele that is expressed only when there is no dominant allele present Mendel’s Theory

20. Mendel’s Theory • Law of Segregation of Alleles: • When an organism produces gametes, each pair of alleles on homologous chromosomes separate in Meiosis I and each gamete has an equal chance of receiving either one of the alleles

21. Mendel’s Theory: Law of Segregation of Alleles

22. Mendel’s Theory • GENOTYPE:a specific combination of alleles in an individual….. the “genes” an individual has • example: AA, Aa, or aa • PHENOTYPE : the detectable trait or traits that result from the genotype of an individual….. the “physical appearance” an individual has • example: normal, normal, albino

23. Mendel’s Theory • GENOTYPE DETERMINES PHENOTYPE !

24. Mendel’s Theory The genotype of each of the peas is ____________.

25. Mendel’s Theory • The phenotype of each of the following is _____.

26. Mendel’s Theory • Homozygous:describes an individual that carries two identical alleles of a gene • Example: PP or pp • Heterozygous:describes an individual that carries two different alleles of a gene • Example: Pp

27. Mendel’s Theory • Mendel’s 2nd Experiments • Dihybrid crosses: involves test crossing two characters • Law of Independent Assortment: during gamete formation, the alleles on non-homologous chromosomes segregate independently

28. Mendel’s Theory

29. Problem Solving: Producing True-Breeding Seeds • Textbook page 271 • Work in table groups • Define the problem • Organize information • Create solution • Present to class

30. Mendel’s Theory • When genes are close together on same chromosome they will rarely separate independently so are said to be “linked”.

31. Modeling Mendel’s Laws • Punnett Square: a graphic used to predict the results of a genetic cross

32. Modeling Mendel’s Laws • A Punnett Square shows all the genotypes that could possibly result from any given cross match.

33. Modeling Mendel’s Laws • Monohybrid Homozygous Cross • Draw a Punnett Square crossing homozygous Y (for yellow seed color) with homozygous y (for green seed color) • What is the ratio of yellow to green seeds ? • Monohybrid Heterozygous Cross • Draw a Punnett Square crossing 2 plants that are heteroygous for Y • What is the ratio of yellow to green seeds?

34. Modeling Mendel’s Laws • Test Cross: used to test an individual whose phenotype for a given characteristic is dominant but its genotype is unknown • Individual is crossed with a known homozygous recessive • If unknown is homozygous dominant all offspring will show dominant phenotype • If unknown heterozygous for the trait then ½ the offspring will show dominant phenotype & ½ will show recessive trait

35. Modeling Mendel’s Laws • Using Probability • Probability: the likelihood that a specific event will occur; expressed in mathematics • Probabilities are used to predict the likelihood that specific alleles will be passed down to offspring

36. Quick Lab: Probabilities: page 268 • Notebook: page 15 • Everyone completes this: • Follow procedure • Answer analysis questions 1 - 2

37. Modeling Mendel’s Laws • Pedigree: a diagram that shows the occurrence of a genetic trait in several generations of a family • Genetic Disorder: an inherited disease that is caused by a mutation in a gene or by a chromosome defect

38. Pedigrees

39. Pedigrees

40. PEDIGREES

41. Modeling Mendel’s Laws • Pedigrees can help answer 3 aspects of inheritance: • Sex linkage • Dominance • Heterozygocity

42. Modeling Mendel’s Laws • Sex-Linked Gene • Gene located on either the X or Y chromosomes • Females have 2 X chromosomes so rarely show the recessive phenotype; males have just 1 X chromosome so will show the trait for a single recessive allele for genes on the X chromosome • If find a trait that is more common in males than females it is likely sex-linked

43. Genes on Sex Chromosomes

44. Sex-Linked

45. Modeling Mendel’s Laws 2. Dominant or Recessive? • If a child shows a trait and neither parent shows the trait it is likely a recessive trait

46. Modeling Mendel’s Laws 3. Heterozygous or Homozygous? • Recessive trait in a child shows parents had to be heterozygous for the trait

47. Beyond Mendelian Heredity • Polygenic Character: a character influenced by more than 1 gene • includes many characters in humans • Eye color • Skin color • Height

48. Beyond Mendelian Heredity • Incomplete Dominance: the phenotype for a heterozygous individual is intermediate between the homozygous dominant phenotype and the homozygous recessive phenotype

49. Beyond Mendelian Heredity • Genes that are said to have 3 or more possible alleles are said to have multiple alleles • Example: human’s ABO blood types

50. Beyond Mendelian Heredity • Codominance: a condition in which both alleles for a gene are fully expressed in the phenotype