additional genetic patterns mendel’s peas other patterns complete dominance incomplete dominance...

Additional Genetic Patterns Additional Genetic Patterns

Mendel’s peasMendel’s peas Other PatternsOther PatternsComplete Complete DominanceDominance

Incomplete DominanceIncomplete Dominance

CodominanceCodominance

Lethal AllelesLethal AllelesHierarchy of DominanceHierarchy of Dominance

Two alleles Two alleles per geneper gene

Multiple AllelesMultiple Alleles

One gene affects One gene affects one traitone trait

……Many traits (Pleiotropy)Many traits (Pleiotropy)

Two (or more) genes affect Two (or more) genes affect one trait (Gene Interactions one trait (Gene Interactions and Polygenic Traits)and Polygenic Traits)

Additional Genetic Patterns Additional Genetic Patterns

Mendel’s peasMendel’s peas Other PatternsOther PatternsCould not observe Could not observe gender-specific traitsgender-specific traits

Sex-influenced traits Sex-influenced traits

Sex-limited traitsSex-limited traits

Equal contributions Equal contributions from both parents from both parents

Cytoplasmic InheritanceCytoplasmic InheritanceGenetic Maternal EffectGenetic Maternal Effect

Genomic ImprintingGenomic Imprinting

Trait expressed at Trait expressed at same level and stage same level and stage of lifeof life

AnticipationAnticipation

No environmental No environmental influence influence

Environmental EffectsEnvironmental Effects

Incomplete Dominance Incomplete Dominance

Incomplete dominance: neither allele Incomplete dominance: neither allele masks the other and both are observed masks the other and both are observed as a blending in the heterozygoteas a blending in the heterozygote

Four o’clock flowersFour o’clock flowersR = red, R’ = whiteR = red, R’ = white

RR x R’R’RR x R’R’Red WhiteRed White

RR’RR’ pinkpink

Incomplete DominanceIncomplete Dominance

RR’ x RR’RR’ x RR’Pink x PinkPink x Pink

Genotypic Ratio: Genotypic Ratio: Phenotypic Ratio:Phenotypic Ratio:

Multiple Alleles Multiple Alleles

• Multiple alleles: three or more Multiple alleles: three or more alleles exist for one traitalleles exist for one trait

(Note: A diploid individual can only (Note: A diploid individual can only carry two alleles at once.) carry two alleles at once.)

Blood TypeBlood Type AlleleAllele

Type AType A IIAA

Type BType B IIBB

Type OType O ii

Codominance Codominance

Codominance: Neither allele masks the Codominance: Neither allele masks the other so that effects of both alleles are other so that effects of both alleles are observed in heterozygote without observed in heterozygote without blendingblending

IIA A == IIB B > i> i

IIA A and Iand IBB are codominant. are codominant.IIA A and Iand IBB are completely dominant over i. are completely dominant over i.

Codominance Codominance

PhenotypePhenotype GenotypeGenotype Gene Gene

ProductProduct

Antibodies Antibodies PresentPresent

Type AType A IIAAIIAA or I or IAAii Antigen AAntigen A Anti-BAnti-B

Type BType B IIBBIIBB or I or IBBii Antigen BAntigen B Anti-AAnti-A

Type ABType AB IIAAIIBB Antigen AAntigen A

andand

Antigen BAntigen B

Neither Neither

Anti-A norAnti-A nor

Anti-BAnti-B

Type OType O iiii nonenone Anti-A Anti-A

andand

Anti-BAnti-B

Antigens on Red Blood Cells Antigens on Red Blood Cells

IAi IBi

IAIB

Inheritance of Rh Factor Inheritance of Rh Factor

PhenotypePhenotype Genotype*Genotype* Gene Gene

ProductProduct

Antibodies Antibodies PresentPresent

Rh PositiveRh Positive RR or RrRR or Rr Rhesus ProteinRhesus Protein None None

Rh NegativeRh Negative rrrr NoneNone None None unless unless exposedexposed

*There are multiple alleles for the Rhesus protein *There are multiple alleles for the Rhesus protein (R(R11, R, R22, R, R33, etc.) and all are dominant to the multiple, etc.) and all are dominant to the multiple alleles for the absence of Rhesus protein (ralleles for the absence of Rhesus protein (r11, r, r22, r, r33, etc.) ., etc.) .

Multiple Alleles and CodominanceMultiple Alleles and Codominance Type A, Rh positive x Type B, Rh negativeType A, Rh positive x Type B, Rh negative(father is Type O, Rh negative) (mother is Type O)(father is Type O, Rh negative) (mother is Type O)

Phenotypic Ratio of OffspringPhenotypic Ratio of Offspring

Lethal AllelesLethal Alleles

Example: Manx catExample: Manx catMMLL = tailless, lethal in homozygote = tailless, lethal in homozygotem = tailm = tail

Tailless male x Tailless femaleTailless male x Tailless female

Hierarchy of DominanceHierarchy of Dominance

Example: hair curlingExample: hair curlingSSww = wooly S = wooly Scc= curly S= curly Swawa= wavy s = straight= wavy s = straightSSww>> SScc> S> Swawa>> ss


Dad Colavito has wavy hair.Dad Colavito has wavy hair.Mom Colavito has curly hair.Mom Colavito has curly hair.Their daughter Jean has straight hair.Their daughter Jean has straight hair.What are the expected genotypic and What are the expected genotypic and phenotypic ratios for their offspring?phenotypic ratios for their offspring?

SSww>> SScc> S> Swawa>> ss


SSww> S> Scc> S> Swawa>> ss

Dad C x Mom CDad C x Mom CWavy CurlyWavy Curly

Bonus: What is Dr. C’s genotype?Bonus: What is Dr. C’s genotype?

Pleiotropic EffectsPleiotropic Effects

One gene affects many One gene affects many phenotypic characteristicsphenotypic characteristics

AlleleAllele SS S’S’

Gene ProductGene Product Hemoglobin AHemoglobin A Hemoglobin SHemoglobin S

Cell ShapeCell Shape RoundRound Sickled under Sickled under low Olow O22 tension tension

Response to Response to MalariaMalaria

SusceptibleSusceptible Resistant in SS’ Resistant in SS’ genotypegenotype

Example of Polygenic InheritanceExample of Polygenic Inheritance Two genes affecting skin coloration Two genes affecting skin coloration

Number of Number of Dominant Dominant

AllelesAlleles

Skin Color*Skin Color*

(Phenotype)(Phenotype)

GenotypesGenotypes % Pigmentation% Pigmentation

00 WhiteWhite aabbaabb 0-11%0-11%

11 Light BlackLight Black Aabb or aaBbAabb or aaBb 12-25%12-25%

22 Medium BlackMedium Black AAbb or AaBb or AAbb or AaBb or aaBBaaBB

26-40%26-40%

33 Dark BlackDark Black AABb or AaBBAABb or AaBB 41-55%41-55%

44 Darkest BlackDarkest Black AABBAABB 56-78%56-78%

*Based on a study conducted in Jamaica. *Based on a study conducted in Jamaica.

Polygenic InheritancePolygenic Inheritance

Medium Black WomanMedium Black Woman(mother is white)(mother is white)

X Darkest Black ManX Darkest Black Man

Interacting Genes Affecting a Interacting Genes Affecting a Single CharacteristicSingle Characteristic

eg. Skin coloration in snakeseg. Skin coloration in snakes

One gene One gene O = orange pigmentO = orange pigment o = no orange pigmento = no orange pigment

Second geneSecond geneBB = black pigment= black pigmentb = no black pigmentb = no black pigment


eg. Skin coloration in snakeseg. Skin coloration in snakes Oo Bb x Oo BbOo Bb x Oo Bb

OO BBOO BB OOBbOOBb Oo BBOo BB Oo BbOo Bb

OO BbOO Bb OO bbOO bb Oo BbOo Bb Oo bbOo bb

Oo BBOo BB Oo BbOo Bb o o BBo o BB o o Bbo o Bb

Oo BbOo Bb Oo b bOo b b o o Bbo o Bb o o b bo o b b

OBOB ObOb o Bo B o bo b

OBOB

ObOb

o Bo B

o bo b


eg. Skin coloration in snakeseg. Skin coloration in snakes

OoBb x OoBbOoBb x OoBb

9/16 O_B_9/16 O_B_ 3/16 O_bb 3/16 O_bb 3/16 ooB_ 3/16 ooB_ 1/16 oobb 1/16 oobb

EpistasisEpistasis

• An allele of one gene masks the expression of An allele of one gene masks the expression of alleles of another gene and expresses its own alleles of another gene and expresses its own phenotype instead.phenotype instead.

• Gene that masks = epistatic gene Gene that masks = epistatic gene • Gene that is masked = hypostatic geneGene that is masked = hypostatic gene• Genes that code for enzymes that are Genes that code for enzymes that are

upstream in a biochemical pathway usually upstream in a biochemical pathway usually exert epistasis (“standing on”).exert epistasis (“standing on”).

Recessive EpistasisRecessive Epistasis

Epistatic gene exerts its affect with Epistatic gene exerts its affect with homozygous recessive genotype.homozygous recessive genotype.

eg. Petal color in blue-eyed Mary plantseg. Petal color in blue-eyed Mary plantsmm= magenta, ww =white, W__M__= mm= magenta, ww =white, W__M__=

blueblue

WW

enzyme 1enzyme 1

MM

enzyme 2enzyme 2

Precursor 1Precursor 1 Precursor 2 Precursor 2blue anthocyaninblue anthocyanin colorlesscolorless magenta magenta

Recessive EpistasisRecessive Epistasis

eg. Petal color in blue-eyed Mary plantseg. Petal color in blue-eyed Mary plants

WW w Mw M m x Wm x W w Mw M mm

9/16 W9/16 W __ M__ __ M__ 3/16 W __3/16 W __ mmmm3/16 w w M__3/16 w w M__1/16 w w mm1/16 w w mm

Phenotypic ratio:Phenotypic ratio:

Duplicate Recessive EpistasisDuplicate Recessive Epistasis

Defective products of recessive alleles of two Defective products of recessive alleles of two different genes interfere with separate steps different genes interfere with separate steps in a biochemical pathway. in a biochemical pathway.

eg. Petal color in harebell flowerseg. Petal color in harebell flowers ww = white, bb = white, W_ B_ = blueww = white, bb = white, W_ B_ = blue

Precursor 1Precursor 1 Precursor 2 Precursor 2blue anthocyaninblue anthocyanin colorlesscolorless colorless colorless

WW

enzyme 1enzyme 1

BB

enzyme 2enzyme 2

Duplicate Recessive EpistasisDuplicate Recessive Epistasis

eg. Petal color in harebell flowerseg. Petal color in harebell flowers

WW w Bw B b x Wb x W w Bw B bb

9/16 W9/16 W __B__ __B__ 3/16 W __3/16 W __ b b b b 3/16 w w B__3/16 w w B__1/161/16 w w bw w b b b


Dominant EpistasisDominant Epistasis

Epistatic gene exerts its affect with the Epistatic gene exerts its affect with the presence of a dominant allele. presence of a dominant allele.

eg. Fruit color in summer squasheg. Fruit color in summer squashY = yellow, yy = green; Y = yellow, yy = green;

W inhibits either color = white; W inhibits either color = white; w has no effect on color w has no effect on color

Dominant EpistasisDominant Epistasis

eg. Fruit color in summer squasheg. Fruit color in summer squash

WW w Y y x Ww Y y x W w Y yw Y y

9/16 W9/16 W __ Y__ __ Y__ 3/16 W __3/16 W __ yyyy3/16 w w Y__3/16 w w Y__1/16 w w yy1/16 w w yy


Duplicate Dominant EpistasisDuplicate Dominant Epistasis

eg. Fruit shape in Shepherd’s purseeg. Fruit shape in Shepherd’s purse

A_ or B_ = heart shapeA_ or B_ = heart shape

aa and bb = narrow shapeaa and bb = narrow shape

Duplicate Dominant EpistasisDuplicate Dominant Epistasis

eg. Fruit shape in Shepherd’s purseeg. Fruit shape in Shepherd’s purse A_ or B_ = heart aa and bb = narrow A_ or B_ = heart aa and bb = narrow

A a BA a B b x A a Bb x A a B b b

9/16 A__B__9/16 A__B__3/16 A__b b3/16 A__b b

3/16 a3/16 a a B__a B__1/16 a1/16 a a b ba b b


Interaction between Sex and HeredityInteraction between Sex and Heredity

Sex-influenced Sex-influenced characteristic characteristic

Determined by autosomal genesDetermined by autosomal genes

Expression differs by genderExpression differs by gender

Male pattern baldness Male pattern baldness Dominant in males, recessive in females Dominant in males, recessive in females

John AdamsJohn Adams John Quincy AdamsJohn Quincy Adams

Interaction between Sex and HeredityInteraction between Sex and Heredity

Sex-limited Sex-limited characteristic characteristic

Determined by autosomal genesDetermined by autosomal genes

Expressed only in one genderExpressed only in one gender

Cock feathering, autosomal recessive Cock feathering, autosomal recessive Expressed only in malesExpressed only in males

Cock-feathered maleCock-feathered male Hen-feathered femaleHen-feathered female Hen-feathered maleHen-feathered male

Interaction betweenInteraction between

Sex and HereditySex and Heredity

Cytoplasmic InheritanceCytoplasmic Inheritance

Genes found on chromosomes Genes found on chromosomes of cytoplasmic organellesof cytoplasmic organelles

Inherited from the maternal Inherited from the maternal parent due to contribution of parent due to contribution of cytoplasm in ovum cytoplasm in ovum

Leaf variegation Leaf variegation caused by inheritance caused by inheritance of variable chloroplast of variable chloroplast

genotypes genotypes

Interaction betweenInteraction between

Sex and HereditySex and Heredity

Genetic Maternal EffectGenetic Maternal Effect

Phenotype of offspring Phenotype of offspring depends on genotype of depends on genotype of the maternal parentthe maternal parent

Direction of snail shell Direction of snail shell coiling is determined coiling is determined

by genotype of female by genotype of female parent parent

Interaction Between Sex and HeredityInteraction Between Sex and Heredity Genomic Genomic ImprintingImprinting

Expression of autosomal genes Expression of autosomal genes differs depending on whether they differs depending on whether they are inherited from the male or are inherited from the male or female parentfemale parent

Prader-Willi SyndromePrader-Willi SyndromeDeletion on chromosome 15 Deletion on chromosome 15

inherited from father inherited from father

Angelman SyndromeAngelman SyndromeDeletion on chromosome 15 Deletion on chromosome 15

inherited from mother inherited from mother

Anticipation Anticipation

Trait is more strongly expressed or Trait is more strongly expressed or expressed earlier in succeeding generationsexpressed earlier in succeeding generations

Huntington Huntington DiseaseDisease

Increase in number of trinucleotide Increase in number of trinucleotide repeats in gene for protein Huntingtin repeats in gene for protein Huntingtin leads to lethal neurodegenerative leads to lethal neurodegenerative disorder with personality changes and disorder with personality changes and uncontrollable movements. uncontrollable movements.

Number of repeats expands with Number of repeats expands with succeeding generations. Disease occurs succeeding generations. Disease occurs earlier and is more severe. earlier and is more severe.

Allen(46,13)age 50

Linda(6,22)

Kristen(64,22)age 40

Ann(64,22)age 39

Andrew(69,6)age 37

Debbie(13,6)

Greg(11,19)

Nathaniel(72,19) age 35

Bill(8,12)

Paula(13,12)

Evan(not tested)

Christina(93,7)age 26

Joseph(7,6)

Jama(7,18)

Expansion of the Trinucleotide Repeat for Huntington’s Disease

Environmental Effects Environmental Effects

Phenotype is dependent upon the presence Phenotype is dependent upon the presence of a specific environment. of a specific environment.

The temperature-sensitive product of the himalayan allele The temperature-sensitive product of the himalayan allele is inactivated at high temperatures.is inactivated at high temperatures.

Penetrance and ExpressivityPenetrance and Expressivity• Penetrance = percentage of individuals with a Penetrance = percentage of individuals with a

given genotype who exhibit the phenotypegiven genotype who exhibit the phenotype

• Expressivity = extent to which genotype is Expressivity = extent to which genotype is expressed at the phenotypic level (may be due to expressed at the phenotypic level (may be due to allelic variation or environmental factors)allelic variation or environmental factors)

additional genetic patterns mendel’s peas other patterns complete dominance incomplete dominance...

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