Neo Mendelian Genetics

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Neo-Mendelian Genetics Neo-Mendelian Genetics 1. Incomplete Dominance 1. Incomplete Dominance 2. Co-dominance 2. Co-dominance 3. Multiple alleles 3. Multiple alleles 4. Epistasis 4. Epistasis 5. Sex-limited Phenotypes 5. Sex-limited Phenotypes 6. Sex-influenced Phenotypes 6. Sex-influenced Phenotypes 7. Penetrance and Expressivity 7. Penetrance and Expressivity 8. X-linked 8. X-linked 9. Temperature 9. Temperature

Transcript of Neo Mendelian Genetics

Page 1: Neo Mendelian Genetics

Neo-Mendelian GeneticsNeo-Mendelian Genetics

1. Incomplete Dominance1. Incomplete Dominance2. Co-dominance2. Co-dominance3. Multiple alleles3. Multiple alleles4. Epistasis4. Epistasis5. Sex-limited Phenotypes5. Sex-limited Phenotypes6. Sex-influenced Phenotypes6. Sex-influenced Phenotypes7. Penetrance and Expressivity7. Penetrance and Expressivity8. X-linked8. X-linked9. Temperature9. Temperature

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Neo-Mendelian GeneticsNeo-Mendelian Genetics

Incomplete DominanceIncomplete Dominance A. Intermediate phenotypeA. Intermediate phenotype B. No dominant phenotypeB. No dominant phenotype

Red Snapdragon X White Red Snapdragon X White SnapdragonSnapdragon

All FAll F11 pink pink

FF1 1 X FX F11(all heterozygous pink)(all heterozygous pink)

FF22 = 1 red, 2 pink, 1 white = 1 red, 2 pink, 1 white

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Neo-Mendelian GeneticsNeo-Mendelian Genetics

Codominance (multiple alleles)Codominance (multiple alleles) A. Both alleles are expressedA. Both alleles are expressed B. Any given gene may have more B. Any given gene may have more

than twothan two allelesalleles C. Karl Landsteiner discovered ABO C. Karl Landsteiner discovered ABO blood typeblood type D. I = isoagglutinogenD. I = isoagglutinogen

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Neo-Mendelian GeneticsNeo-Mendelian Genetics

E. 4 blood phenotypes by 3 allelesE. 4 blood phenotypes by 3 alleles F. IF. IAA, I, IBB, , iiii G. Type A person will have A antigen onG. Type A person will have A antigen on erythrocyte and anti-B antibodyerythrocyte and anti-B antibody H. Type O person will have no antigens H. Type O person will have no antigens and both AB antibodiesand both AB antibodies I. Universal donor = OI. Universal donor = O J. Universal recipient = ABJ. Universal recipient = AB

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Neo-Mendelian GeneticsNeo-Mendelian Genetics

Background on Human Blood Background on Human Blood GroupsGroups

1. A and B antigens are carbohydrate 1. A and B antigens are carbohydrate groups groups

bound to lipid moleculesbound to lipid molecules 2. Most people have H-substance consisting 2. Most people have H-substance consisting of 3 sugars Gal, N-acetylglucosamine, of 3 sugars Gal, N-acetylglucosamine, and fucoseand fucose

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Neo-Mendelian GeneticsNeo-Mendelian Genetics

Background on Human Blood Background on Human Blood GroupsGroups

3. I3. IAA allele responsible for an enzyme allele responsible for an enzyme that attaches N-acetylgalactosaminethat attaches N-acetylgalactosamine to the H-substanceto the H-substance 4. I4. IBB allele = responsible for an enzyme allele = responsible for an enzyme that attaches galactose to the that attaches galactose to the H-H-

substancesubstance 5. 5. ii = allele responsible for no addition = allele responsible for no addition of a sugarof a sugar

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Neo-Mendelian GeneticsNeo-Mendelian Genetics

Bombay PhenotypeBombay Phenotype A. Woman is Bombay phenotypically OA. Woman is Bombay phenotypically O B. Her parents were ABB. Her parents were AB C. Genetically the woman was BC. Genetically the woman was B D. Rare recessive mutation D. Rare recessive mutation hh E. H-substance lacked fucoseE. H-substance lacked fucose F. IF. IAA or I or IBB alleles could not recognize alleles could not recognize

H-substanceH-substance

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Neo-Mendelian GeneticsNeo-Mendelian Genetics

Secretor LocusSecretor Locus A. Ability to secrete A/B antigens into A. Ability to secrete A/B antigens into

bodybody secretionssecretions B. Influenced by a dominant allele B. Influenced by a dominant allele

Se/Se or Se/seSe/Se or Se/se

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What happens when What happens when more thanmore than

one gene interacts to one gene interacts to control the expression control the expression

of a phenotype?of a phenotype?

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EpistasisEpistasis

A. Modification of A. Modification of 9 : 3 : 3 : 19 : 3 : 3 : 1 B. Genes exerting influence on another B. Genes exerting influence on another

genegene C. C. Example #1Example #1 9 : 79 : 7

White-flowered sweet peasWhite-flowered sweet peas AAbb X aaBB FAAbb X aaBB F11 AaBb all purple AaBb all purple

AaBb X AaBb FAaBb X AaBb F22 9 purple and 7 white9 purple and 7 white presence of at least one dominant allele of each presence of at least one dominant allele of each

of two gene pairs is essential in order for of two gene pairs is essential in order for flowers to be purpleflowers to be purple

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EpistasisEpistasis

Example #2Example #2 12 : 3 : 112 : 3 : 1 Fruit color in summer squashFruit color in summer squash - dominant alleles of one locus masks - dominant alleles of one locus masks

expression at the second locusexpression at the second locus A-B-(or bb) = White aabb = greenA-B-(or bb) = White aabb = green aaB- = YellowaaB- = Yellow AaBb X AaBb FAaBb X AaBb F11 12 white, 3 yellow, 12 white, 3 yellow,

1 green1 green

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EpistasisEpistasis

Example #3Example #3 9 : 6 : 19 : 6 : 1 Summer SquashSummer Squash - dominant allele at either locus - dominant allele at either locus

ensures a sphere shaped fruit/both ensures a sphere shaped fruit/both genes are influenced equivalentlygenes are influenced equivalently

AABB(disc) X aabb(long) = FAABB(disc) X aabb(long) = F11 all disc all disc

AaBb X AaBb = FAaBb X AaBb = F22 9 disc, 6 sphere, 9 disc, 6 sphere, 1 long 1 long

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EpistasisEpistasis

Example #4Example #4 13 : 313 : 3 White Leghorn Chickens (CCII) X White White Leghorn Chickens (CCII) X White

Wyandotte chickens (ccii) = FWyandotte chickens (ccii) = F11 CcIi CcIi (white feathers)(white feathers)

CcIi X CcIi = FCcIi X CcIi = F22 13 white, 3 colored13 white, 3 colored C allele = necessary for colored feathersC allele = necessary for colored feathers I allele = inhibitor of feather colorationI allele = inhibitor of feather coloration I allele = dominant over C alleleI allele = dominant over C allele

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EpistasisEpistasis

Example #5Example #5 9 : 4 : 39 : 4 : 3 ““AgoutiAgouti” coat color” coat color A = dominant allele for agouti hair A = dominant allele for agouti hair

colorcolor aa- = black coat coloraa- = black coat color C- = dominant allele necessary for C- = dominant allele necessary for

hair pigmenthair pigment cc = albinocc = albino

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EpistasisEpistasis

AACC = agoutiAACC = agouti AaCc = agoutiAaCc = agouti aaC- = blackaaC- = black aacc = albinoaacc = albino AACC X aacc = FAACC X aacc = F11 AaCc AaCc

AaCc X AaCc FAaCc X AaCc F22 9 agouti, 4 albino, 9 agouti, 4 albino, 3 black3 black

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EpistasisEpistasis Example #6Example #6 9 : 3 : 3 : 19 : 3 : 3 : 1

1. Very similar ratios as the F1. Very similar ratios as the F22 offspring of a dihybrid offspring of a dihybrid cross.cross.2. If Rose mates with Single, Rose is completely 2. If Rose mates with Single, Rose is completely dominant over Single (Fdominant over Single (F11 all Rose, F all Rose, F22 3:1, Rose:Single) 3:1, Rose:Single)3. If Pea mates with Single, Pea is completely 3. If Pea mates with Single, Pea is completely dominant over Single (Fdominant over Single (F11 all Pea, F all Pea, F22 3:1, Pea:Single) 3:1, Pea:Single)

4. If Rose and Pea mate, all F4. If Rose and Pea mate, all F11 walnut. When two walnut. When two

walnuts mate from Fwalnuts mate from F11, F, F22 expresses expresses

9 walnut: 3 rose: 3 pea : 1 single9 walnut: 3 rose: 3 pea : 1 single

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X LinkageX Linkage

A. Documented in 1910 by Thomas A. Documented in 1910 by Thomas MorganMorgan

B. studies of white eye mutation in B. studies of white eye mutation in DrosophilaDrosophila

C. X and Y chromosomes pair C. X and Y chromosomes pair during meiosis at regions called during meiosis at regions called pseudoautosomal regions (PAR)pseudoautosomal regions (PAR)

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X LinkageX Linkage

D. Y chromosome believed to be D. Y chromosome believed to be largely blank largely blank

E. Located on only one X chromosomeE. Located on only one X chromosome F. Reciprocal cross = same conditions F. Reciprocal cross = same conditions

different sexesdifferent sexes G. Phenotypic traits controlled by G. Phenotypic traits controlled by

recessive X linked genes are passed recessive X linked genes are passed from homozygous mother to all sons “ from homozygous mother to all sons “ Crisscross pattern of inheritance”Crisscross pattern of inheritance”

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X LinkageX Linkage

H. Morgan’s work supported H. Morgan’s work supported chromosomes theory of inheritance chromosomes theory of inheritance (genes transmitted on specific (genes transmitted on specific chromosomes)chromosomes)

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Sex Influences PhenotypeSex Influences Phenotype

A. A. Sex-limited inheritanceSex-limited inheritance - only one - only one sex can express phenotypesex can express phenotype

B. B. Sex-influenced inheritanceSex-influenced inheritance - sex - sex determines how phenotype is seendetermines how phenotype is seen

C. Autosomal genes involvedC. Autosomal genes involved D. Hormones involvedD. Hormones involved

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Sex Influences PhenotypeSex Influences Phenotype

Example #1Example #1 Hen feathers or Cock Hen feathers or Cock FeathersFeathers

Female MaleFemale Male hh hen feathers hh cock hh hen feathers hh cock

feathersfeathers *sex limited**sex limited*

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Sex Influences PhenotypeSex Influences Phenotype

Example #2Example #2 Pattern BaldnessPattern Baldness Female MaleFemale Male BB Bald BaldBB Bald Bald Bb Not Bald BaldBb Not Bald Bald bb Not Bald Not bb Not Bald Not

BaldBald *even BB in females is less *even BB in females is less

pronounced than in males**pronounced than in males**

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Modification of Gene Modification of Gene ExpressionExpression

A. A. Penetrance Penetrance - percentage of - percentage of individuals that show at least some individuals that show at least some degree of expression of a mutant degree of expression of a mutant genotypegenotype

B. B. ExpressivityExpressivity - range of expression of - range of expression of mutant genotypemutant genotype

C. C. Genetic BackgroundGenetic Background 1. Suppression - no expression of a mutant 1. Suppression - no expression of a mutant

phenotypephenotype 2. Position effect - physical location of gene2. Position effect - physical location of gene

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Modification of Gene Modification of Gene ExpressionExpression

D. D. Temperature EffectTemperature Effect PrimrosePrimrose Red flowers @ 23 Red flowers @ 23ooCC

White flowers @ 18White flowers @ 18ooCC Himalayan RabbitsHimalayan Rabbits - dark fur around - dark fur around

areas that are cooler, light fur areas that are cooler, light fur around areas that are warmer. around areas that are warmer. Pigment enzyme functional at lower Pigment enzyme functional at lower temperatures.temperatures.

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Modification of Gene Modification of Gene ExpressionExpression

Nutritional EffectNutritional Effect (nutritional (nutritional mutants) = inactivity of enzymes of a mutants) = inactivity of enzymes of a biosynthetic pathwaybiosynthetic pathway

-useful to genetic studies in bacteria-useful to genetic studies in bacteria -phenylketonuria-phenylketonuria -galactosemia-galactosemia -lactose intolerance-lactose intolerance

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Modification of Gene Modification of Gene ExpressionExpression

Onset of Genetic ExpressionOnset of Genetic Expression stage of an organisms life spanwhere a stage of an organisms life spanwhere a

gene is expressedgene is expressed Tay Sachs disease(aut. Rec.) = by age 3Tay Sachs disease(aut. Rec.) = by age 3 Lesch-Nyhan Syndrome (X-linked rec) = 8 Lesch-Nyhan Syndrome (X-linked rec) = 8

monthsmonths Duchenne Muscular Dystrophy(X-inked Duchenne Muscular Dystrophy(X-inked

rec) = 3 to 5 yearsrec) = 3 to 5 years Huntington Disease (aut. Dom) = 38 years Huntington Disease (aut. Dom) = 38 years

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Modification of Gene Modification of Gene ExpressionExpression

““Gene expression and the resultant Gene expression and the resultant phenotype are often modified phenotype are often modified through the interactions between an through the interactions between an individual’s particular genotype and individual’s particular genotype and the internal and external the internal and external environment”environment”