polygenic inheritance
DESCRIPTION
Polygenic Inheritance. Trait controlled by 2 or more genes May be on the same or different chromosomes Shows a range , intermediate is most common phenotype Upper and lower case letters used. Many variations in skin color. Skin color: A polygenic trait. - PowerPoint PPT PresentationTRANSCRIPT
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Polygenic Inheritance
Trait controlled by 2 or more genes
May be on the same or different chromosomes
Shows a range, intermediate is most common phenotype
Upper and lower case letters used
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Many variations in skin color
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Skin color: A polygenic traitSkin color: A polygenic traitDetermining # of Genes Involved in Skin Color
Observed distribution of skin color
Expected distribution- 1 gene
Expected distribution- 4 genes
Expected distribution- 3 genes
Range of skin colorLight Right
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Skin ColorSkin color is actually due to 5 genes
Genotypes darkest to lightest:AABBCCDDEE would be darkestAaBbCcDdEe would be mediumaabbccddee would be lightest
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Influence of external environment
In arctic foxes temperature has an effect on the expression of coat color. In winter, fur is white.
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Arctic Fox in summer coloration: influence of external environment
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External influences can also be seen in leaves. Leaves can have different sizes, thicknesses, and shapes depending on the amount of light they receive.
Influence of external environment
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The internal environments of males and females are different because of hormones and structural differences.
An organism’s age can also affect gene function.
Influence of internal environment
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Peacock (male) Peahen (female)
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Sex-linked TraitsSex-linked Traits
Traits Traits (genes) located on the(genes) located on the sex chromosomessex chromosomes
Sex chromosomes are Sex chromosomes are X and X and YY
XXXX genotype for females genotype for femalesXYXY genotype for males genotype for malesMany Many sex-linked traitssex-linked traits carried carried on on XX chromosome chromosome
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Thomas Hunt Morgan
American biologistWorked with fruit flies also called DrosophilaFound that the gene for eye color is located on the X chromosome
Discovered sex-linked inheritance
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Sex-linked TraitsSex-linked Traits
Sex ChromosomesSex Chromosomes
XX chromosome - female Xy chromosome - male
fruit flyeye color
Example: Example: Eye color in fruit Eye color in fruit fliesflies
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Sex-linked Trait Sex-linked Trait ProblemProblem
Example: Eye color in fruit flies(red-eyed male) x (white-eyed female) XRY x XrXr
Remember: the Y chromosome in males does not carry traits.
RR = red eyedRr = red eyedrr = white eyedXY = maleXX = female
XR
Xr Xr
Y
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Sex-linked Trait Solution:Sex-linked Trait Solution:
XR Xr
Xr Y
XR Xr
Xr Y
50% red eyed female50% white eyed male
XR
Xr Xr
Y
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Female CarriersFemale CarriersFemales are carriers of sex-linked
traits if they have the heterozygous genotype.
Males cannot be carriers because they only have one X chromosome.
Female parents who are carriers, pass sex-linked traits to all children, but males are usually the ones who express the trait.
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Examples of Sex-linked Traits: Red-green colorblindnessMale Pattern BaldnessHemophiliaDuchenne Muscular DystrophyHairy Ears
Y Chromosome
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