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Genetics The Scientific Study of Inheritance. Terms Allele Barr body Codominance Dihybrid cross Dominant Epistasis Genotype Heterozygous Homozygous.

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Presentation on theme: "Genetics The Scientific Study of Inheritance. Terms Allele Barr body Codominance Dihybrid cross Dominant Epistasis Genotype Heterozygous Homozygous."— Presentation transcript:

1 Genetics The Scientific Study of Inheritance


3 Terms Allele Barr body Codominance Dihybrid cross Dominant Epistasis Genotype Heterozygous Homozygous

4 Inbreeding Incomplete dominance Linkage Locus Multi-allelic Phenotype Pleiotropy Polygenic Recessive Sex-linked

5 Gregor Mendel Monk Austria; Czech republic 1 st to analyze inheritance in a scientific manner Scientific method Careful record-keeping

6 Gregor Mendel Studied garden peas –Easy to grow –Produce lots of offspring –Easily distinguished characteristics Fruit flies - today

7 Gregor Mendel Parents pass factors to their offspring that are responsible for traits Factors = genes Garden peas self-pollinate True-breedingTrue-breeding = parents produce offspring identical to themselves

8 Gregor Mendel Control cross-pollination Cross-pollination produced hybrids –Called a cross HybridsHybrids = offspring with mixed traits TraitsTraits = inherited characteristic

9 Crossed pure-breeding and got one trait. What happened to the white trait?

10 Gregor Mendel Allowed F 1 s to self-pollinate Produced F 2 generation F 2 s; 705 purple; 224 white 3:1 ratio The heritable factor for white was masked but was not destroyed

11 Gregor Mendel - 4 Hypotheses: 1.There are alternate forms for factors that control heredity 2.For each characteristic, there are 2 factors inherited; one from each parent 3. A gamete carries only one form for each factor; during fertilization, the 2 factors unite 4. One form of the factor is fully expressed (visible) and the other has no effect


13 Modern Genetics FactorsgenesFactors = genes Alternate forms = allelesAlternate forms = alleles GenesGenes = sections of DNA; code for making proteins Expression of proteins determines trait Dominant Allele= allele that IS expressed; protein is expressed (made) Recessive Allele = allele that is NOT expressed (made); or masked; protein is not made

14 Structure Of A Chromosome Chromosomes are homologous pairs –Same size, banding, centromere location and genes Made of DNA Sections of chromosomes are genes

15 Chromosome 1Homologue Gene Allele Two alleles to a gene; alleles may be dominant or recessive From momFrom dad


17 GenotypeGenotype = an organisms genetic makeup –PP PhenotypePhenotype = an organisms expressed or physical traits –Purple Modern Genetics

18 Mendels Principle of Segregation: Law of Segregation

19 Principle of Segregation All organisms have 2 sets of homologous chromosomes; one from each parent; –Diploid One allele located on each chromosome; one from mom, one from dad –2 alleles = 1 gene

20 Principle of Segregation Pairs of alleles separate (segregate) during gamete formation 1 form of a factor goes into 1 gamete while the other form separates and goes into another gamete (handout) LocusLocus = location of a gene on a chromosome; loci (pl.) Alleles are at the same locus on each homologous chromosome

21 HomozygousHomozygous = both alleles for the trait are the same (homo) –PP, pp = homozygous HeterozygousHeterozygous = the two alleles are different –Pp = heterozygous Principle of Segregation

22 Fertilization During fertilization, the sperm unites with the egg diploid zygote1 haploid sperm + 1 haploid egg = 1 diploid zygote Which sperm unites with which egg is by random chance –Flipping a coin

23 This is too hard to do!!!!

24 Use The Laws of Probability Probability = chance that something will occur How can we predict what will happen easier? Punnett SquarePunnett Square How does it work, you say? Im so glad you asked ……

25 Punnett Square 1.Use letters to represent each allele a. Use the CAPITAL for dominant and small case for recessive b. Ex. P = purple; p = white c.T = tall; t = short d.Y – yellow; y - green

26 2. Draw a square PURPLE PURPLE x white

27 3.Determine what letters to use to represent the alleles Example: PURPLE a. Cross a PURPLE with a white flower. PURPLE P = PURPLE b. PURPLE is dominant over white in pea plants so use P = PURPLE and p = white c. Every gene has 2 alleles so use 2 letters

28 PP pp Crossing a homozygous purple flower with a homozygous recessive white flower PP pp X

29 4.Separate letters (alleles) around the square – this represents segregation PP p p BE CAREFUL HOW YOU MAKE YOUR LETTERS!! PP pp

30 5. Combine the letters (alleles) into each box of the square PP PURPLE PP PURPLE PP x white pp p p P P P P p p pp

31 6. Determine the results PP PP PURPLE PP x pp = 4 Pp; and 4 PURPLE p p PpPpPpPp PpPpPpPp PpPpPpPp PpPpPpPp Genotype = 4 Pp PURPLE Phenotype = 4 PURPLE Purple

32 Results: Genotype – combination of letters (alleles); –Pp Phenotype – appearance (what do they LOOK like? –Purple

33 What If You Crossed heterozygous purple with heterozygous purple? PpPp Pp x Pp PpPpPpPp PpPpPpPp

34 Separate letters (alleles) around the square P PPpPPp p p P PPpPPp

35 Combine the letters (alleles) in the squares P p p P PP P p p P pp Purple Purple Purplewhite

36 P PP Pp x Pp p PPP PpPpPpPp p pp p P Genotypes – Phenotypes – 1 - PP 2 - Pp 1- pp 3 - PURPLE 1 - white PurplePurple Purplewhite

37 Practice Problems Tall is dominant to short What genotypic and phenotypic results would be expected if you crossed a HOMOZYGOUS tall with a HOMOZYGOUS short?

38 Practice Problems What genotypic and phenotypic results would be expected if you crossed a HOMOZYGOUS tall with a HOMOZYGOUS short? TT tt

39 TT Tt t t Genotypes Tt Phenotypes tall 100% tall Tall

40 In pea plants, yellow is dominant to green. What results would be expected if you crossed a homozygous yellow with a homozygous green? Homozygous = same Yellow – Y; green – y Homozygous yellow = YY Homozygous green = yy Practice:

41 YY y y YyYyYyYy YyYy YyYy Yellow Genotype – 4 Yy Phenotype – 4 yellow; 100% yellow

42 Black fur is dominant to brown fur in mice. What results should you expect if you crossed a homozygous black with a homozygous brown? –Black is dominant so use B; brown - b –Homozygous black = BB –Homozygous brown = bb Practice

43 BB b b BbBb BbBb Black Genotype – 100% Bb Phenotype – 100% black

44 Law of Independent Assortment Are Traits Inherited Together (dependently) or Separately (independently)?

45 Law of Independent Assortment Round (R) is dominant to wrinkled (r) Yellow (Y) is dominant to green (y) Result from crossing two traits? –If you inherit a dominant trait does the other trait also have to be dominant? Dihybrid cross – result of crossing two traits together

46 Dihybrid Cross Homozygous (pure-breeding) round (RR), and yellow (YY) with: Homozygous recessive; wrinkled (rr), green (yy)

47 Dihybrid Cross Are the two traits inherited together (in a package) or can they be inherited separately? Mendel crossed the Ps (yellow, round x green, wrinkled) –F 1 s were all dominant (yellow, round) Allowed the F 1 s to self-pollinate

48 Dihybrid Cross 9:3:3:1 ratio 9/16 = yellow, round 3/16 = yellow, wrinkled 3/16 = green, round 1/16 = green, wrinkled


50 Independent Assortment: YyRr YR Yr yR yr Parent: 1 & 2

51 YRYRYrYryRyRyryr YRYR YrYr yRyR yryr Law of Independent Assortment Yy Rr

52 YRYryRyr YRYYRRYYRrYyRRYyRr YrYYRrYYrrYyRrYyrr yRYyRRYyRryyRRyyRr yrYyRrYyrryyRryyrr

53 Law of Independent Assortment: Each pair of alleles segregates independently of other pairs of alleles Can recombine independently of each other Genetic variationGenetic variation –Biggest cause of genetic variation in sexually reproducing organisms

54 Independent Assortment Budgies inherit two colors INDEPENDENTLY Color (Yellow) or no color on the outer surface of the feather MelaninMelanin or no melanin in the inner core of the feather

55 Variation and Patterns of Variation Wild type - most common traits in the wild –Budgies = green feathers Knowing patterns and rules of inheritance allows breeders to produce blues, yellows, and whites

56 Budgie Color Two genes inherited separately 1.Outside color of feather 2.Inside color of feather Independent assortment; the two characteristics are inherited independently of each other

57 Green Green = Y_B_

58 Blue = yyB_

59 Yellow; Y_bb

60 White; yybb

61 Test Cross How can We Use Genetics to Determine if Our Organism is Pure- breeding?

62 Test cross Mate an individual whose genotype is not known (dominant phenotype) with a homozygous recessive for that trait Ex. Is your favorite Labrador a pure black or does he carry a recessive allele?

63 Test cross Cross the unknown with a homozygous recessive Eight puppies born, 3 are brown (recessive) ?

64 BB b b Bb If the unknown is homozygous (pure) then all the offspring are dominant

65 Bb b b Bbbb Bb bb If the unknown is heterozygous (carrier) then some offspring are recessive

66 Variations of Mendel 1.Complete dominance 2.Incomplete dominance 3.Codominance 4.Multiple alleles 5.Pleiotropy 6.Polygenic inheritance 7.Linkage

67 Incomplete Dominance Dominant allele does not totally mask recessive allele Some recessive trait is expressed: blended Redpink Red x white = pink

68 Curly hair + straight hair = wavy

69 Incomplete Dominance Heterozygotes express a trait between the dominant and recessive Familial hypercholesterolemia –hh = very high cholesterol –Hh = mild cholesterol –HH = low cholesterol; normal

70 Codominance Both traits are EQUALLY dominant; Both traits are expressed (not blended) –Roan color –Sickle cell –Blood types

71 Codominance Two different traits and both show equally –Roan color –Blood types

72 Blood Types Antigens = proteins on the surface of red blood cells (RBCs) Antibodies = proteins floating in the plasma of blood that bind with foreign proteins (antigens) Antibodies stick to foreign antigens forming a clot

73 Blood Types B into A causes a clot A into B causes a clot

74 Blood Types Antibodies will be the opposite of the antigens –A blood will have B antibodies –B blood will have A antibodies Antibodies are like guard dogs; they attack foreign cells with the wrong antigens

75 Blood Types CodominanceCodominance Multiple allelesMultiple alleles = 1 gene but three possible allele combinations –A, B, O

76 Blood Types: Phenotypes AntigensAntigens = proteins on the surface of cells (RBCs) Cell-to-cell recognition AntibodiesAntibodies = proteins floating in the plasma of blood that bind with foreign proteins (antigens)

77 Blood Types: Phenotypes Antibodies agglutinate to antigens that are foreign Agglutinate = clot, clump B into A causes agglutination

78 Blood Types: Phenotypes Blood type = type of antigens on the surface Antibodies will be the opposite of the antigens A blood will have B antibodies

79 A antigens A B Antibodies

80 B antigens B A Antibodies

81 B antigens B B Antibodies B antibodies attach to B antigens; causes blood to agglutinate Person with A blood:

82 A antigens A A Antibodies Person with B blood: A antigens are attacked by A antibodies

83 A, B antigens ABAB No antibodies Person with AB blood:

84 No antigens O A and B antibodies Person with O blood:

85 Blood Types: Genotypes Dominant allele = I Recessive allele = i (inability) II, Ii, ii Dominant allele can carry A or B I a or I B

86 Blood Types 2 alleles for each gene: A = I A I A or I A i B = I B I B or I B i AB = I A I B O (zero) = ii

87 phenotypegenotypeantigensantibodies Receive From: AIAIAIAiIAIAIAi AAnti-BA or O BIBIBIBiIBIBIBi BAnti-AB or O ABABIAIBIAIB A,BA,BNoneA, B, O OiiNoneAnti-A Anti-B O


89 How to do Punnett Squares With Blood Types:

90 IAIA i IAIA IAIA IAIAIAIA IAIAIAIA I A i Heterozygous Homozygous

91 Can 2 people With A and B Blood Have a Child With O Blood?

92 IAIA i IBIB i IAIBIAIB I A i I B i i Heterozygous A Heterozygous B AB B A O

93 Pleiotropy One gene has multiple effects Sickle-cell anemia; p. 160 –Abnormal blood cells –Difficulty breathing –Brain, heart, kidney damage


95 Pleiotropy : Heterozygote Advantage High incidence of sickle-cell in areas where there is a lot of malaria Malaria does not effect sickle-cell People w/ sickle-cell dont suffer malaria

96 Polygenic Inheritance Multiple genes produces a continuous effect; very dark-very light –Skin, hair, eye color –6 – 10 alleles –AABBCC - aabbcc

97 Linkage Early 1900s; TH Morgan Fruit flies Inheritance patterns did not follow Mendelian Laws of Probability (?) Genes are linked


99 Linkage Genes on the same chromosome are inherited together Sex – linked genes Gene located on the sex chromosome (usually X)


101 Sex linkage and Punnett Squares

102 Linkage The sex-linked trait is usually on the X chromosome X X = female X Y = male X H = normal X h = hemophilia


104 Hemophilia Sex-linked, recessive disorder Bleeders disease; lack protein for blood clotting Czar Nicholas son Nicki; p. 168

105 XHXH XHXH XHXH Y X H X H Y Normal phenotypes:

106 XHXH XHXH XhXh Y X H X H X h X H YX h Y Hemophilia phenotype:

107 Sex-linked Traits: Hemophilia Duchennes Muscular dystrophy Color-blindness Mostly males Smartness

108 Sex-linked Traits: Y Chromosome Maleness

109 Censored



112 Pedigrees Tracing traits back over generations Dominance does NOT mean that a phenotype is normal or more common Wild type

113 Pedigrees Dominance = heterozygote displays the trait Recessive expression occurs only if the genotype is homozygous bb, tt, ff

114 Pedigrees Used to predict probability of genetic disorders CarriersCarriers = individuals who do not express the trait but have the recessive allele in their genotype


116 Human Disorders Single gene: 2 types; –Dominant expression –Recessive expression

117 Human Disorders: Dominant Only requires one allele for trait to be expressed –Polydactyly; multiple fingers –Achondroplasia; dwarfism, heterozygotes

118 Human Disorders: Dominant Most dominant disorders are not lethalMost dominant disorders are not lethal –Huntingtons disease –Huntingtons disease ; midlife expression, degeneration of the nervous system –Hypercholesterolemia –Hypercholesterolemia – high cholesterol; heart disease

119 Human Disorders: Recessive Homozygous for the disorder to be expressed –Cystic fibrosis; –Sickle cell anemia –Tay-Sachs disease –PKU

120 Fetal Testing AmniocentesisAmniocentesis = removal of amniotic fluid (surrounds the developing baby); 20 ml –Biochemical tests (spina bifida, infections) –Cells karyotyping (Downs, Tay-Sachs)

121 Fetal Testing Chorionic villus samplingChorionic villus sampling (CVS) fetal cells removed from placenta –Karyotyped quickly

122 Fetal Testing UltrasoundUltrasound = view of baby FetoscopyFetoscopy = direct view of baby

123 Recessive Disorders Cystic fibrosis – whites; build up of mucus in lungs, pancreas


125 Recessive Disorders Sickle cell anemiaSickle cell anemia – Black and SE Asia; 1/500 (lethal), 1/10 carrier; –Codominant – one allele is normal, other forms hemoglobin that crystallizes in low oxygen

126 Recessive Disorders Tay-SachsTay-Sachs – Jewish; lack gene that produces enzyme that breaks down lipids in the brain; causes brain degeneration, lethal by age 3-4 PKU – phenylketonuria; lack the gene needed to make the enzyme that breaks down phenylalanine. Phenylalanine accumulates causing nervous disorders. Treated with diet

127 Pedigrees Tracing traits back over generations Dominance does NOT mean that a phenotype is normal or more common Wild type

128 Pedigrees Used to predict probability of genetic disorders CarriersCarriers = individuals who do not express the trait but have the recessive allele in their genotype

129 Pedigree Family tree Shows how a trait is passed down from one generation to the next = male = female

130 Pedigree number 1

131 Pedigree number 2

132 Pedigree number 3



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