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

ww

W

W

W

w

w w

w w

Ww

Ww Ww

Ww

Ww Ww

ww ww

Ww

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