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Advanced Punnet Squares Pages 183-184, 244 Test Cross: Used to determine if the dominant phenotype is homozygous or heterozygous. To perform the test cross you breed the dominant phenotype with the recessive phenotype. The recessive phenotype must by homozygous Ex: Black Bunny (BB or Bb) x White Bunny (homozygous recessive) B B b Bb Bb b Bb Bb B b b Bb bb b Bb bb If test cross produces a homozygous recessive offspring, we conclude the parent was heterozygous. Incomplete Dominance: The allele doesn’t completely mask the recessive allele and the phenotypes mix. Ex: Red & White flowers. Red allele: R White allele: r RR= Red flower rr= White flower Rr= Pink Flower R r Genotype Ratio: 1:2:1 R RR Red Rr Pink Phenotype Ratio: 1:2:1 r Rr Pink rr White Co- Dominance: Alleles are expressed when present Heterozygous shows both traits at the same time Ex: Sickle cell anemia Normal Red Blood Cells: N Sickle Red Blood Cells: S NN= All normal cells NS= Half normal cells SS= Only sickle cells N S Genotype Ratio: 1:2:1 N NN Normal NS Both Phenotype Ratio: 1:2:1 S NS Both SS Sickle Sex-Linked Traits: diseases/genes found only on the X sex chromosomes. Gender is determined by the sex chromosomes (#23 for humans) XX= female XY =male Recessive Sex linked traits are more common in males than females because if the male receives a recessive gene then there is no other gene present to mask it. Ex: Colorblindness Normal Color Vision Gene: XR Deficient Color Vision Gene: Xr NN= All normal cells SS= Only sickle cells NS= Half normal cells XR Xr XR XR XR XR Xr Y XR Y Xr Y OFFSRING XR Xr XR Normal Female Carrier Female Y Normal Male Color Blind Male Genotype Phenotype XR XR Female : Normal Color Vision XR Xr Female : Normal Color Vision but a carrier of the recessive gene Female: Color Blind Xr Xr Very Rare: Father was colorblind and mother was carrier XR Y Xr Y Male: Normal Color Vision Male: Color Blind All his daughters will be carriers