Genetics Beyond Mendel
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Transcript of Genetics Beyond Mendel
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Genetics Beyond MendelGenetics Beyond Mendel
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Incomplete DominanceIncomplete DominancePhenotype is a blend of the alleles
An intermediate is seen
Four o’clocks
Homozygous Red Heterozygous Homozygous White
Sometimes written: C and C1
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Incomplete Dominance - HumansIncomplete Dominance - Humans
Hair FolliclesHair Follicles– Curly hair is homozygous recessiveCurly hair is homozygous recessive– Straight hair is homozygous Straight hair is homozygous
dominantdominant– Heterozygous individuals have Heterozygous individuals have
wavy hairwavy hair
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Incomplete Dominance - HumansIncomplete Dominance - Humans
Cholesterol GeneCholesterol Gene– Homozygous Homozygous
dominant – Very dominant – Very high cholesterolhigh cholesterol
– Heterozygous – Heterozygous – high cholesterolhigh cholesterol
– Homozygous Homozygous recessive – normal recessive – normal cholesterolcholesterol
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Multiple Allele TraitsMultiple Allele Traits
More than two alleles for a traitMore than two alleles for a trait
Only two forms are inheritedOnly two forms are inherited
Can have co-dominance Can have co-dominance
Can have a hierarchy of dominanceCan have a hierarchy of dominance– hair color in mice determined by a single gene hair color in mice determined by a single gene
with alleles for black, brown, agouti, gray, with alleles for black, brown, agouti, gray, albinoalbino
agouti > black > brown > albino. agouti > black > brown > albino.
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CodominanceCodominance
Both alleles are expressed Both alleles are expressed at the same timeat the same time
Roan horse appears grey but has a mixture of white and black hairs
Hybrid camellia
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Blood TypesBlood Types
Multiple Alleles (3) and Co dominantMultiple Alleles (3) and Co dominantA, B, O alleles produce:A, B, O alleles produce:
AA = AAA = A BB = BBB = B
AO = AAO = A BO = BBO = B
AB = ABAB = AB OO = OOO = O
Four blood type phenotypesFour blood type phenotypes
Sometimes written ISometimes written IAA I IBB i i
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Polygenic InheritancePolygenic Inheritance
More than one set of More than one set of alleles controls a traitalleles controls a trait
Skin color has three Skin color has three different setsdifferent sets
Effect is additiveEffect is additive
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Environment and InheritanceEnvironment and Inheritance
Gene expression is influenced by the Gene expression is influenced by the environmentenvironment
Chemicals, temperature, pH levels, radiation, Chemicals, temperature, pH levels, radiation, nutrition can all be factorsnutrition can all be factors
Himalayan rabbits – fur changes color with exposure to cold
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Turtles Turtles – Sex determined by temperature of eggs Sex determined by temperature of eggs – Males produced at lower incubation Males produced at lower incubation
temperatures than females temperatures than females – At temperatures around 30 degrees Celsius At temperatures around 30 degrees Celsius
only female turtles ariseonly female turtles arise
Lizards and crocodiliansLizards and crocodilians– Females produced at lower temperatures, Females produced at lower temperatures,
males at higher temperatures males at higher temperatures
Environment and InheritanceEnvironment and Inheritance
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Gender InheritanceGender Inheritance
Due to one set of Due to one set of chromosomes in chromosomes in humanshumansXX = female XX = female XY = MaleXY = MaleOne X must come from One X must come from mothermotherSperm can donate an X Sperm can donate an X or Yor YSex is determined at Sex is determined at fertilization fertilization
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Sex-linked InheritanceSex-linked InheritanceSex linked traits:– Genes that are carried by either sex chromosome– Y linked genes appear on Y chromosome– X linked genes appear on the X chromosome
Only men inherit Y chromosomes– Only ones to inherit Y-linked traits
Men and women both inherit X chromosomes– Both can get the X-linked traits
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Males –
Genes on the X chromosome that do not code for gender are expressed
Even recessive genes
No corresponding gene on the Y chromosome.
Sex-linked InheritanceSex-linked Inheritance
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Females –
Recessive allele on one X chromosome is masked by a dominant allele on the other
Women are frequently carriers of X-linked traits but rarely have them expressed in their own phenotypes.
Sex-linked InheritanceSex-linked Inheritance
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Sex-linked InheritanceSex-linked InheritanceX chromosome carries coat pigment genes
One X chromosome randomly becomes deactivated.
The active X chromosome determines the color in that particular cell
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A human female "carrier“ heterozygous for sex-linked trait causing red-green color blindness
(recessive) marries a normal male
What proportion of their male progeny will have red-green color blindness?
Sex-linked InheritanceSex-linked Inheritance
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Genotype of parentsGenotype of parentsMother: heterozygous for red green color blindness
Father: homozygous dominant on X no allele on Y
½ of the daughters
are carriers
½ of the daughters
are normal
½ of the sons are
color blind
½ of the sons are normal
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The two most noted X linked genetic disorders are hemophilia and color blindness
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Pedigree DiagramPedigree Diagram
Visual chart of a family’s genetic historyVisual chart of a family’s genetic history
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Pedigree DiagramPedigree Diagram
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Pedigree DiagramPedigree Diagram
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Pedigree DiagramPedigree Diagram