Transcript 6. Hair color genetics 2014

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?