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Deducing Genotypes
Song Hee Bae
IB1 Biology
Pedigree Charts
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How a trait can pass
Whether dominant or recessive
Whether sex-linked or not
Sex-linkage
o Ex) color blindness, hemophilia
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Similar to family tree
Squares = male
Circles = female
Shaded = affected
Not shaded = unaffected
Huntington’s Disease
• Whether mother’s genotype is Hh or HH
• Consider genotypes of next generation
• Affected people
o First daughter
o Forth son
o Fifth son
• Unaffected people
o Second and third sons
o Grand daughter
• Mother must be Hh
Using Test Crosses
• To distinguish between
Dominant X Dominant / Dominant X Recessive
• A subject is crossed with homozygous
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W – long ears
w – short ears
Vocabulary
• Pedigree chart: diagram which are constructed to show biological
relationships.
• Sex linkage: any genetic trait whose allele has its locus on the X
chromosome.
• Test cross: a method to distinguish whether the individuals that might
have the same phenotype are influenced by dominant / recessive
allele.
Reference
• IB Study guides page 29
• Pearson Biology SL page 105, 108~109