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Chapter 11 -- Basic Genetics. Inheritance Gregor Mendel 1822-1884.

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Presentation on theme: "Chapter 11 -- Basic Genetics. Inheritance Gregor Mendel 1822-1884."— Presentation transcript:

1 Chapter Basic Genetics

2 Inheritance

3 Gregor Mendel

4 Mendels pea garden in Brno

5 Verhandlungen des naturforschenden Vereines in Brünn. Brünn: Vereines, Mendels paper

6 Why did Mendel choose peas?

7 Mendels Peas

8 Two Characters Seed Coat Flower color

9 Two traits per character Rough Smooth

10 Two traits per character Purple flowers White flowers

11 Traits are alternative forms of characters white or purple smooth or rough

12 Brother Mendel! We grow tired of peas!

13

14 Controlling the mating

15 No question as to parentage of offspring

16 Compare

17 1. Start with true breeding plants. 2. Cross alternative forms among these true- breeders. Mendels experimental design

18 P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers

19

20 3. Allowed progeny (F1) to self-fertilize and examined offspring 4. Count the number of offspring of each type Mendels experimental design

21 P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers

22 Monohybrid crosses: examining one trait at a time What Mendel found- monohybrid crosses

23 P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers Monohybrid Cross

24 What Mendel found F1 generation P Generation (true-breeding parents) F 1 Generation (hybrids) Purple flowers White flowers All plants had purple flowers

25 P Generation (true-breeding parents) F 1 Generation (hybrids) F 2 Generation Purple flowers White flowers All plants had purple flowers F1 x F1

26 F2: purple and white 705 purple flowered plants 224 white flowered plants 3:1 ratio What Mendel found F2 generation

27 F 1 Generation (hybrids) All plants had purple flowers F2 Generation 705 purple 224 white 3:1 ratio

28 Mendels 7 pea traits

29 1. Alternative versions of genes lead to variations in inherited characters. Alternative versions are called alleles 2. Each individual receives 2 alleles. –homozygotes: 2 copies of identical allele –heterozygotes: two different alleles Mendels model

30 3. In heterozygotes only the dominant form of allele will be expressed. –genotype: alleles present –phenotype: physical appearance 4. Alleles segregate from one another into gametes (Law of segregation) Mendels model

31 Allele for purple flowers Homologous pair of chromosomes Allele for white flowers Locus for flower-color gene Chromosomes, genes and alleles ……..

32 Genes control characters e.g., flower color

33 Genes control characters Traits are alternative forms of characters e.g., white or purple

34 Traits are alternative forms of characters Alleles are alternative forms of a gene Genes control characters

35

36 Human Chromosomes

37 Genes Alleles and

38 Variation within a population

39 Capital letter for dominant allele; lower case letter for recessive allele Example flower color: P = dominant allele p = recessive allele Mendel used symbols to interpret results

40 Phenotype: purple Genotype: PP or Pp

41 Phenotype: white Genotype: pp

42 Phenotype Purple 3 Genotype PP (homozygous Pp (heterozygous Pp (heterozygous pp (homozygous Ratio 1:2:1 White Ratio 3:1 1

43 Cross plant with unknown genotype with homozygous recessive The testcross

44 The Punnett square Reginald C. Punnett

45

46 PP x pp p p P P Pp

47 Dominant phenotype, unknown genotype: PP or Pp? If PP, then all offspring purple: pp P P Pp If Pp, then 1 2 offspring purple and 1 2 offspring white: pp P P pp Pp Recessive phenotype, known genotype: pp The testcross

48 Different types of Inheritance

49 Dominant - Recessive

50 purple Pp PP white pp

51 Incomplete Dominance

52 Incomplete dominance When alleles are not fully dominant or fully recessive in heterozygotes

53 Multiple Alleles: ABO Blood Group Codominance No single allele is dominant Each allele has its own effect.

54 Codominance

55 Type A: adds galactosamine –I A I A, I A i Type B: adds galactose –I B I B, I B i Type AB: adds galactosamine and galactose –I A I B Type O: no sugar added –ii Multiple Alleles: ABO Blood Group

56 ABO Blood Groups

57 Pleiotropic Effects One allele have multiple effects

58 Environmental effects

59 THE CHROMOSOMAL BASIS OF INHERITANCE

60 Chromosomes and Mendelian Inheritance

61 Allele for purple flowers Homologous pair of chromosomes Allele for white flowers Locus for flower-color gene Chromosomes, genes and alleles …….. and loci

62 Thomas Hunt Morgan (1866 – 1945) Drosophila

63

64 Human Chromosomes

65 Sex Linkage XX female XY male

66 Human sex chromosomes

67 Color blindness Sex Linked traits Male pattern baldness

68 Chromosomal problems

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73 Klinefelter syndrone

74 Recessive genes can be carried without being expressed

75 Queen Victoria and hemophilia

76

77 Sickle cell anemia

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