Genetics of Genetics of HairHair

Simple Trait, Complex Simple Trait, Complex GeneticsGenetics

What determines our natural What determines our natural hair color?hair color?

► Brunette ladies can give birth to blonde children if the Brunette ladies can give birth to blonde children if the father is blonde. (Can it happen if the father is brunette?)father is blonde. (Can it happen if the father is brunette?)

► Brunette + Blonde parents = either hair color in children. Brunette + Blonde parents = either hair color in children. (Does the sex of the parent matter?)(Does the sex of the parent matter?)

► Not really enough information in this pedigree to make Not really enough information in this pedigree to make strong conclusionsstrong conclusions

► Brunette ladies can give birth to blonde children if the Brunette ladies can give birth to blonde children if the father is blonde. (Can it happen if the father is brunette?)father is blonde. (Can it happen if the father is brunette?)

► Brunette + Blonde parents = either hair color in children. Brunette + Blonde parents = either hair color in children. (Does the sex of the parent matter?)(Does the sex of the parent matter?)

► Not really enough information in this pedigree to make Not really enough information in this pedigree to make strong conclusionsstrong conclusions

Why use Model Organisms?Why use Model Organisms?

Purebred labrador breedingPurebred labrador breeding

After many breedings…After many breedings…

►Which phenotype is dominant?Which phenotype is dominant?

Breeding F1 generation Breeding F1 generation puppiespuppies

►Observations?Observations?►Conclusions?Conclusions?

Homozygous dominant, Homozygous dominant, Homozygous recessive or Homozygous recessive or

Heterozygous?Heterozygous?►TTTT►BbBb►eeee►EEEE►LlLl►PPPP►PpPp►pppp

►GGGG►HHHH►HhHh►AaAa►AAAA►OoOo►oooo►aaaa

PracticePractice

►Draw a Punnett square crossing TT and TTDraw a Punnett square crossing TT and TT►Draw a Punnett square crossing TT and TtDraw a Punnett square crossing TT and Tt►Draw a Punnett square crossing Tt and TtDraw a Punnett square crossing Tt and Tt►Draw a Punnett square crossing tt and ttDraw a Punnett square crossing tt and tt

►Draw a Punnett square crossing a Draw a Punnett square crossing a homozygous dominant brown dog with a homozygous dominant brown dog with a heterozygous brown dogheterozygous brown dog

What is happening?What is happening?►Let’s review the parents…Let’s review the parents…

►Dominant – an allele that is expressed in the Dominant – an allele that is expressed in the heterozygous conditionheterozygous condition

►cross = breeding resulting in offspringcross = breeding resulting in offspring►OffspringOffspring►PurebredPurebred►P generationP generation►FF11 Generation Generation

FertilizationFertilization

The gametes of the F1 gen…The gametes of the F1 gen…

►GameteGamete► FertilizationFertilization► ZygoteZygote

► Genotype► Homozygous recessiveHomozygous recessive► Homozygous dominantHomozygous dominant► HeterozygousHeterozygous

Punnett SquaresPunnett Squares

““Ask a Geneticist”Ask a Geneticist”

►Read the article and answer the post-Read the article and answer the post-reading questions.reading questions.

►You will have 20-25 mins. Then we will You will have 20-25 mins. Then we will hold a more detailed discussion on hair hold a more detailed discussion on hair color.color.

►Hair color writing quiz on Wednesday!!!Hair color writing quiz on Wednesday!!!

Best explanation of a Best explanation of a genetically dominant trait? genetically dominant trait?

(Poll everywhere)(Poll everywhere)http://www.polleverywhere.com/multiple_choice_polls/qsv3ClzjmdZAcQs

►Most common in populationMost common in population►Most beneficial trait availableMost beneficial trait available►What appears when both parents have What appears when both parents have

dominant traitdominant trait►What appears when an individual has What appears when an individual has

two different genes for a traittwo different genes for a trait►What destroys the recessive traitWhat destroys the recessive trait

Are all hair colors just Are all hair colors just variations on brown?variations on brown?

What causes the reddish What causes the reddish shades?shades?

How hair grows: Hair How hair grows: Hair AnatomyAnatomy

How hair grows: Hair How hair grows: Hair AnatomyAnatomy

My explanation for My explanation for variations…variations…

MelanocytesMelanocytes

MelaninsMelanins►Photoprotectant pigment in mammals.Photoprotectant pigment in mammals.

Why would we want it???Why would we want it???

►Made by melanocytes in skin and hair Made by melanocytes in skin and hair folliclesfollicles

►EumelaninEumelanin Brown or blackBrown or black Amount mattersAmount matters 4 4 pairspairs of genes of genes POLYGENICPOLYGENIC

►PheomelaninPheomelanin► RedRed► Scots/IrishScots/Irish

►MC1R MC1R genegene►Turns Ph Turns Ph Eu Eu

Chromosomes from 1 human Chromosomes from 1 human cellcell

Locations of hair color genesLocations of hair color genes

MC1R MC1R gene location & its gene location & its functionfunction

Polygenic Polygenic = controlled by = controlled by multiple gene pairsmultiple gene pairs

Why two types of Why two types of Melanin?Melanin?

►Which colors of hair are generally Which colors of hair are generally associated with very associated with very darkdark skin tones? Why skin tones? Why is this?is this? advantage ?advantage ? geographic regions?geographic regions?

►Which skin tones are generally associated Which skin tones are generally associated with with redred hair? hair? advantage ?advantage ? geographic regions?geographic regions?

What about albinos?What about albinos?

Why does hair turn gray?Why does hair turn gray?

Why does hair turn gray?Why does hair turn gray?

What is melanoma?What is melanoma?

Trying to Trying to change our change our phenotypes!phenotypes!

Hair TextureHair Texture► Totally different genes from hair colorTotally different genes from hair color► Curly and wavy hair is caused by disulfide Curly and wavy hair is caused by disulfide

bonds between the amino acid cysteine in bonds between the amino acid cysteine in the hair structurethe hair structure

►More cysteine = curlierMore cysteine = curlier

Polygenic Polygenic = controlled by = controlled by multiple gene pairsmultiple gene pairs

4) Polygenic traits4) Polygenic traits

►Huge range of phenotypes due to Huge range of phenotypes due to influence of many gene pairs; falls influence of many gene pairs; falls along a bell curvealong a bell curve

Polygenic – finch beak depthPolygenic – finch beak depth

Fig. 14-13

Eggs

Sperm

Phenotypes:

Number ofdark-skin alleles:0 1 2 3 4 5 6

1/646/64

15/6420/64 15/64

6/641/64

AaBbCc AaBbCc

Polygenic - eye colorPolygenic - eye color

True or False?True or False?

► In sexual reproduction, one parent In sexual reproduction, one parent contributes genes for some contributes genes for some characteristics, while the other characteristics, while the other features come from the other parent.features come from the other parent.

Cystic Fibrosis sampleCystic Fibrosis sample

►A child with CF is born to two parents A child with CF is born to two parents without it. What do you know about without it. What do you know about the parents’ genotypes?the parents’ genotypes?