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Observable Patterns of Inheritance

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Presentation on theme: "Observable Patterns of Inheritance"— Presentation transcript:

1 Observable Patterns of Inheritance

2 Can you do this?

3 Terms to Know Probability True-breeding Hybrid Segregation Traits
Genes Homozygous Heterozygous Phenotype Genotype Dominant Recessive

4 Genes Chemical factors that determine traits (units of information)
Analogy: Genes are like a combination of ingredients in a recipe. They code for a specific food. Passed from parents to offspring Each has a specific location (locus) on a chromosome

5 Alleles Different forms of a gene (back to analogy…replacing jiffy p.b. with skippy p.b.) Dominant allele (Uppercase letter) overrules a recessive allele (lowercase letter) that it is paired with

6 Allele Combinations Homozygous =purebred Heterozygous =hybrid
having two identical alleles at a locus AA (dominant expressed) or aa (recessive expressed) Heterozygous =hybrid having two different alleles at a locus Aa (dominant expressed)

7 Genotype & Phenotype Genotype refers to particular genes an individual carries Phenotype refers to an individual’s observable traits Cannot always determine genotype by observing phenotype

8 Tracking Generations Parental generation P mates to produce
First-generation offspring F1 mate to produce Second-generation offspring F2

9 Earlobe Variation Whether a person is born with attached or detached earlobes depends on a single gene Gene has two molecular forms (alleles)


11 Earlobe Variation You inherited one allele for this gene from each parent Dominant allele specifies detached earlobes (E) Recessive allele specifies attached earlobes (e)

12 Dominant & Recessive Alleles
If you have attached earlobes, you inherited two copies of the recessive allele If you have detached earlobes, you may have either one or two copies of the dominant allele

13 Early Ideas About Heredity
People knew that sperm and eggs transmitted information about traits Blending theory Problem: Would expect variation to disappear Variation in traits persists

14 Gregor Mendel Strong background in plant breeding and mathematics
Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring

15 Mendel was born in1822 Austrian monk Studied at the Univ. of Vienna Teacher (High School)

16 Figure 24–5 The Structure of a Flower
Section 24-1 Filament Anther Stigma Style Ovary Carpel Petal Sepal Ovule Stamen

17 The Garden Pea Plant Self-pollinating
True breeding (different alleles not normally introduced) Can be experimentally cross-pollinated

18 How did Mendel fertilize the plants?

19 F1 Results of One Monohybrid Cross

20 Dominant trait is expressed
F M Dominant trait is expressed Recessive appears

21 Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants
Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall

22 F1 Results of Mendel’s Dihybrid Crosses
All plants displayed the dominant form of both traits We now know: All plants inherited one allele for each trait from each parent All plants were heterozygous (AaBb)

23 Principle of Dominance
Some alleles are dominant and others are recessive.

24 Mendel wanted to know if the recessive alleles disappeared or are they still in the f1,just hidden.

25 Principles of Dominance
P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

26 Principles of Dominance
P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

27 Principles of Dominance
P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short

28 Mendel’s Theory of Segregation
An individual inherits a unit of information (allele) about a trait from each parent During gamete formation, the alleles segregate from each other

29 Independent Assortment
Mendel concluded that the two “units” for the first trait were to be assorted into gametes independently of the two “units” for the other trait Members of each pair of homologous chromosomes are sorted into gametes at random during meiosis

30 Independent Assortment
Metaphase I OR A A a a A A a a B B b b b b B B Metaphase II: A A a a A A a a B B b b b b B B Gametes: B B b b b b B B A A a a A A a a 1/4 AB 1/4 ab 1/4 Ab 1/4 aB


32 F2 Results of Monohybrid Cross

33 The physical characteristic
Type of alleles

34 Impact of Mendel’s Work
Mendel presented his results in 1865 Paper received little notice Mendel discontinued his experiments in 1871 Paper rediscovered in 1900 and finally appreciated

35 Probability The likelihood that a particular event will occur.
Flip a coin. We use Punnett Squares

36 D 38- Deduce the probable mode of inheritance of traits (e.g.,

37 Homozygous recessive a a A a aa Aa Homozygous recessive a a A Aa
Punnett Squares of Test Crosses Homozygous recessive a a A a aa Aa Homozygous recessive a a A Aa Two phenotypes All dominant phenotype

38 Punnett Square of a Monohybrid Cross
Female gametes Male gametes A a A a Aa AA aa Dominant phenotype can arise 3 ways, recessive only one

39 Test Cross Individual that shows dominant phenotype is crossed with individual with recessive phenotype Examining offspring allows you to determine the genotype of the dominant individual

40 Tt X Tt Cross

41 Tt X Tt Cross

42 Tt X Tt Cross

43 Genetics Practice Problem 1
What occurs when a purple plant that is heterozygous is fertilized by a white plant? Identify generations Punnett Square Genotypes % Phenotype %

44 Principle of Independent Assortment
The genes for different traits separate independently of one another during the formation of gametes.

45 Figure 11-10 Independent Assortment in Peas

46 Yellow round /16 Green round /16 Yellow wrinkled 3/16 Green wrinkled 1/16 9 : 3 : 3 : 1 Ratio

47 Dihybrid Cross Experimental cross between individuals that are homozygous for different versions of two traits

48 Straight Pinky (Dominant) Bent Pinky (Recessive)
Straight Thumb (Dominant) Curved Thumb (Recessive)

49 Achondroplastic Dwarfism
More Dominant Traits Polydactylism Achondroplastic Dwarfism Tay-Sachs Disease - One Wrong Letter


51 Dominance Relations Complete dominance Incomplete dominance
Heterozygote phenotype is somewhere between that of two homozyotes Codominance Non-identical alleles specify two phenotypes that are both expressed in heterozygotes

52 Flower Color in Snapdragons: Incomplete Dominance
Red-flowered plant X White-flowered plant Pink-flowered F1 plants (homozygote) (homozygote) (heterozygotes)

53 Flower Color in Snapdragons: Incomplete Dominance
Red flowers - two alleles allow them to make a red pigment White flowers - two mutant alleles; can’t make red pigment Pink flowers have one normal and one mutant allele; make a smaller amount of red pigment

54 Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

55 Figure 11-11 Incomplete Dominance in Four O’Clock Flowers

56 Flower Color in Snapdragons: Incomplete Dominance
Pink-flowered plant X Pink-flowered plant White-, pink-, and red-flowered plants in a 1:2:1 ratio (heterozygote) (heterozygote)

57 Incomplete Dominance Neither allele is dominant over the other
Combination of red and white flowers

58 Codominant Sickle Cell Disease ABO Blood Types

59 Pleitropy Alleles at a single locus may have effects on two or more traits Classic example is the effects of the mutant allele at the beta-globin locus that gives rise to sickle-cell anemia

60 Teachers Domain - A Mutation Story

61 Genetics of Sickle-Cell Anemia
Two alleles 1) HbA Encodes normal beta hemoglobin chain 2) HbS Mutant allele encodes defective chain HbS homozygotes produce only the defective hemoglobin; suffer from sickle-cell anemia

62 Pleiotrophic Effects of HbS/HbS
At low oxygen levels, cells with only HbS hemoglobin “sickle” and stick together This impedes oxygen delivery and blood flow Over time, it causes damage throughout the body

63 Blood Typing Karl Landsteiner 1897
Worked at the Univ. of Vienna, Vienna Austria (Sound familiar?) Wanted to find out which red blood cells would clot

64 First found two different groups, A and B
Third group would not clot when exposed to A or B What do you think this was? What about the forth group?

65 Genetics of ABO Blood Types: Three Alleles
Gene that controls ABO type codes for enzyme that dictates structure of a glycolipid on blood cells Two alleles (IA and IB) are codominant when paired Third allele (i) is recessive to others

66 ABO Blood Type: Glycolipids on Red Cells
Type A - Glycolipid A on cell surface Type B - Glycolipid B on cell surface Type AB - Both glyocolipids A & B Type O - Neither glyocolipid A nor B

67 ABO Blood Type: Allele Combinations
Type A - IAIA or IAi Type B - IBIB or IBi Type AB - IAIB Type O - ii

68 ABO and Transfusions Recipient’s immune system will attack blood cells that have an unfamiliar glycolipid on surface Type O is universal donor because it has neither type A nor type B glycolipid

69 Codominance and Multiple Alleles - AB or NOT AB
Codominance - both alleles are dominant IA and IB Multiple Alleles - genes have more than two alleles IA, IB, Ia

70 Figure 14-4 Blood Groups Safe Transfusions Phenotype Antigen on
(Blood Type Antigen on Red Blood Cell Genotype To From

71 Universal Acceptor Universal Donor

72 Rh factor - Another Blood Trait
Pregnancy complications Rh is a type of protein in the blood If an Rh- man reproduces with an Rh + woman complications can occur.

73 Polygenic Traits: Desiree’s Baby Case Study
More than one gene controls a trait Skin color more than one gene, incomplete dominance

74 A,B and C are dark a,b and c are light

75 Sex Linked Traits - traits that are carried on the either the x or y chromosome

76 Figure 14-13 Colorblindness
Father (normal vision) Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind)

77 Figure 14-13 Colorblindness
Father (normal vision) Normal vision Colorblind Male Female Daughter (normal vision) Son (normal vision) Mother (carrier) Daughter (carrier) Son (colorblind)

78 Colorblindness

79 Cystic Fibrosis - Finding Cures is Hard
Sex-Linked Disorder Cystic Fibrosis - Finding Cures is Hard

80 Hairy Pinna - long hair on ears
Male Pattern Baldness (X chromosome) Hairy Pinna - long hair on ears

81 Recessive Disorder Figure 14-8 The Cause of Cystic Fibrosis
Chromosome # 7 CFTR gene The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein. Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane. The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

82 Albinism Phenotype results when pathway for melanin production is completely blocked Genotype - Homozygous recessive at the gene locus that codes for tyrosinase, an enzyme in the melanin-synthesizing pathway




86 Human Genetics

87 Tracing Genes Through Families - Human Pedigrees
Female Partner Male Brothers and Sisters

88 Figure 14-3 A Pedigree A circle represents a female.
A square represents a male. A horizontal line connecting a male and female represents a marriage. A vertical line and a bracket connect the parents to their children. A half-shaded circle or square indicates that a person is a carrier of the trait. A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. A completely shaded circle or square indicates that a person expresses the trait.


90 Ability to roll the tongue in the Senator Family
Tongue Roller - dominant, Non-Tongue Roller - recessive White = tongue roller, Purple = non-roller What are the genotypes of everyone? R = roller, r = non roller

91 George, Sam, Ann, Michael, Daniel and Alan are Rr
Arlene, Tom, Wilma, and Carla are rr Sandra, Tina and Christopher are either RR or Rr

92 Case Study - Hemophilia and the Royal Family


94 1. First, let’s take a look at Queen Victoria’s son Leopold’s family
1. First, let’s take a look at Queen Victoria’s son Leopold’s family. His daughter, Alice of Athlone, had one hemophilic son (Rupert) and two other children—a boy and a girl—whose status is unknown. a) What is the probability that her other son was hemophilic? b) What is the probability that her daughter was a carrier? Hemophilic? c) What is the probability that both children were normal?

95 2. Now for the Spanish connection: Victoria’s youngest child, Beatrice, gave birth to one daughter, one normal son, and two hemophilic sons. Looking at the pedigree of the royal family, identify which of Beatrice’s children received the hemophilic gene; why can you make this conclusion? Notice that Beatrice’s daughter, Eugenie, married King Alfonso XIII of Spain and had six children, one of whom was the father of Juan Carlos, the current King of Spain. Would you predict that Juan Carlos was normal, a carrier, or a hemophilic?

96 3. Alexis did not die from hemophilia
3. Alexis did not die from hemophilia. At the age of fourteen he was executed with the rest of the family. His four oldest sisters were also young and didn’t have children, so we don’t know whether any of them was a carrier. But we can make an estimate. a) What are the probabilities that all four of the girls were carriers of the allele hemophilia? b) Supposing Alexis had lived and married a normal woman, what are the chances that his daughter would be a hemophiliac? c) What are the chances his daughters would be carriers? d) What are the chances that his sons would be hemophiliacs?

97 Homologous chromosomes fail to separate
Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

98 Homologous chromosomes fail to separate
Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

99 Homologous chromosomes fail to separate
Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

100 Epistasis Interaction between the products of gene pairs
Common among genes for hair color in mammals

101 Genetics of Coat Color in Labrador Retrievers
Two genes involved - One gene influences melanin production Two alleles - B (black) is dominant over b (brown) - Other gene influences melanin deposition Two alleles - E promotes pigment deposition and is dominant over e

102 Allele Combinations and Coat Color
Black coat - Must have at least one dominant allele at both loci BBEE, BbEe, BBEe, or BbEE Brown coat - bbEE, bbEe Yellow coat - Bbee, BbEE, bbee

103 Alleles at two loci (R and P) interact
Comb Shape in Poultry Alleles at two loci (R and P) interact Walnut comb - RRPP, RRPp, RrPP, RrPp Rose comb - RRpp, Rrpp Pea comb - rrPP, rrPp Single comb - rrpp

104 Campodactyly: Unexpected Phenotypes
Effect of allele varies: Bent fingers on both hands Bent fingers on one hand No effect Many factors affect gene expression

105 Continuous Variation A more or less continuous range of small differences in a given trait among individuals The greater the number of genes and environmental factors that affect a trait, the more continuous the variation in versions of that trait

106 Human Variation Some human traits occur as a few discrete types
Attached or detached earlobes Many genetic disorders Other traits show continuous variation Height Weight Eye color

107 Temperature Effects on Phenotype
Himalayan rabbits are Homozygous for an allele that specifies a heat-sensitive version of an enzyme in melanin-producing pathway Melanin is produced in cooler areas of body

108 Environmental Effects on Plant Phenotype
Hydrangea macrophylla Action of gene responsible for floral color is influenced by soil acidity Flower color ranges from pink to blue

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