Deducing Genotypes
Song Hee BaeIB1 Biology
Pedigree Charts
• How a trait can pass• Whether dominant or recessive• Whether sex-linked or not• Sex-linkage
o Ex) color blindness, hemophilia• 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 daughtero Forth sono Fifth son
• Unaffected peopleo Second and third sonso Grand daughter
• Mother must be Hh
Using Test Crosses
• To distinguish betweenDominant 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
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