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Transcript
Genetics of Hair Simple Trait, Complex Genetics What determines our natural hair color? ► ► ► Brunette ladies can give birth to blonde children if the father is blonde. (Can it happen if the father is brunette?) Brunette + Blonde parents = either hair color in children. (Does the sex of the parent matter?) Not really enough information in this pedigree to make strong conclusions ► ► ► Brunette ladies can give birth to blonde children if the father is blonde. (Can it happen if the father is brunette?) Brunette + Blonde parents = either hair color in children. (Does the sex of the parent matter?) Not really enough information in this pedigree to make strong conclusions Why use Model Organisms? Purebred labrador breeding After many breedings… ► Which phenotype is dominant? Breeding F1 generation puppies ► Observations? ► Conclusions? ► TT Homozygous dominant, Homozygous recessive or Heterozygous? ► GG ► Bb ► HH ► ee ► Hh ► EE ► Aa ► Ll ► AA ► PP ► Oo ► Pp ► oo ► pp ► aa Practice ► Draw a ► Draw a ► Draw a ► Draw a ► Draw Punnett Punnett Punnett Punnett square square square square crossing crossing crossing crossing TT and TT TT and Tt Tt and Tt tt and tt a Punnett square crossing a homozygous dominant brown dog with a heterozygous brown dog What is happening? ► Let’s review the parents… ► Dominant – an allele that is expressed in the heterozygous condition ► cross = breeding resulting in offspring ► Offspring ► Purebred ► P generation ► F1 Generation Fertilization The gametes of the F1 gen… ► Gamete ► ► Fertilization ► ► Zygote ► ► Genotype Homozygous recessive Homozygous dominant Heterozygous Punnett Squares “Ask a Geneticist” ► Read the article and answer the postreading questions. ► You will have 20-25 mins. Then we will hold a more detailed discussion on hair color. ► Hair color writing quiz on Wednesday!!! Best explanation of a genetically dominant trait? (Poll everywhere) http://www.polleverywhere.com/multiple_choice_polls/qsv3ClzjmdZAcQs ► Most common in population ► Most beneficial trait available ► What appears when both parents have dominant trait ► What appears when an individual has two different genes for a trait ► What destroys the recessive trait Are all hair colors just variations on brown? What causes the reddish shades? How hair grows: Hair Anatomy How hair grows: Hair Anatomy My explanation for variations… Melanocytes Melanins ► Photoprotectant pigment in mammals. Why would we want it??? ► Made by melanocytes in skin and hair follicles ► Pheomelanin ► Eumelanin Brown or black Amount matters 4 pairs of genes POLYGENIC ► Red ► Scots/Irish ► MC1R gene ► Turns Ph Eu Chromosomes from 1 human cell Locations of hair color genes MC1R gene location & its function Polygenic = controlled by multiple gene pairs Why two types of Melanin? ► Which colors of hair are generally associated with very dark skin tones? Why is this? advantage ? geographic regions? ► Which skin tones are generally associated with red hair? advantage ? geographic regions? What about albinos? Why does hair turn gray? Why does hair turn gray? What is melanoma? Trying to change our phenotypes! Hair Texture ► Totally different genes from hair color ► Curly and wavy hair is caused by disulfide bonds between the amino acid cysteine in the hair structure ► More cysteine = curlier Polygenic = controlled by multiple gene pairs 4) Polygenic traits ► Huge range of phenotypes due to influence of many gene pairs; falls along a bell curve Polygenic – finch beak depth Fig. 14-13 AaBbCc AaBbCc Sperm Eggs Phenotypes: 1/ 64 Number of dark-skin alleles: 0 6/ 64 1 15/ 20/ 6 64 64 15/64 /64 2 3 4 5 1/ 64 6 Polygenic - eye color True or False? ► In sexual reproduction, one parent contributes genes for some characteristics, while the other features come from the other parent. Cystic Fibrosis sample ►A child with CF is born to two parents without it. What do you know about the parents’ genotypes?