More Genetics

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More Genetics Pedigrees
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Incomplete Dominance
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(No Transcript)
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Multiple Alleles Codominance
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Polygenic Traits

• Additive effect of multiple genes on a single
  phenotype
• Results in normal distribution
• Examples skin color, height

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Epistasis

• A gene at one locus alters the expression of a
  gene at another locus.
• Example
• Black coat (B) is dominant to brown (b)
• Pigment color (C) is dominant to no pigment color
  (c)

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Effect of Environment on Phenotype
Less acidic soil
More acidic soil
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Pleiotropic Effects
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Pedigree
Male
Female
Heterozygous
Shows trait
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Recessive characteristics

• Inheritance pattern
• Trait tends to skip generations

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Probabilities
Chance of a allele from mom?
Chance of a allele from dad?
Total
x 1 1/2
1/2
1/2
2/2
(1)
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Dominant characteristics

• Trait does not skip generations
• Occurs frequently within a family

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Pedigree Analysis
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Sex linked characteristics

• Tend to occur more in males than in females

• Color-blindness
• Hemophilia

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X-linked Recessives More commonly seen in Males

• Why?
• Males only need one recessive allele to see
  trait.
• E.g. Color-blindness
• XC 92 of alleles
• Xc 8 of alleles

Females Males



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• A woman with normal vision whose father was
  color-blind marries a color-blind male. What
  percent of the couples sons will be color-blind?
• All
• 75
• 50
• 25