Genetics: Punnett Squares Date:______ On an island in the Pacific Ocean, there is a species of birds with different sized beaks, with one specific gene determining their beak size. Birds who are homozygous dominant (BB) or heterozygous (Bb) for this particular gene have small beaks, while birds who are homozygous recessive (bb) for this particular gene have big beaks. For each combination of parents below, predict the frequency with which each phenotype and genotype exists. Make sure to include gametes from each parent. 1) Homozygous Dominant ( BB ) x Homozygous Dominant ( bb ) Genotypes: Phenotypes: BB ______ % Big Beaks ______ % Bb ______ % Small Beaks ______ % Bb ______ % Hint, do your percentages above add up to 100%? 2) Homozygous Recessive ( bb ) x Heterozygous ( Bb ) Genotypes: Phenotypes: BB ______ % Big Beaks ______ % Bb ______ % Small Beaks ______ % Bb ______ % 3) Heterozygous ( Bb ) x Heterozygous ( Bb ) Genotypes: Phenotypes: BB ______ % Big Beaks ______ % Bb ______ % Small Beaks ______ % Bb ______ % Review: What were all the alleles used above? ____________________________________________________ How many possible genotypes do you expect to find within this species, for beak size? _____________ ANSWER KEY Name:___________________ Genetics: Punnett Squares Date:______ On an island in the Pacific Ocean, there is a species of birds with different sized beaks, with one specific gene determining their beak size. Birds who are homozygous dominant (BB) or heterozygous (Bb) for this particular gene have small beaks, while birds who are homozygous recessive (bb) for this particular gene have big beaks. For each combination of parents below, predict the frequency with which each phenotype and genotype exists. Make sure to include gametes from each parent. 1) Homozygous Dominant ( BB ) x Homozygous Dominant ( bb ) B Genotypes: B b Bb Bb b Bb Bb BB ______ 0 % 0 % ______ Bb ______ 100 % 100 % Small Beaks ______ Bb 0 % ______ Phenotypes: Big Beaks Hint, do your percentages above add up to 100%? 2) Homozygous Recessive ( bb ) x Heterozygous ( Bb ) b b B Bb Bb b bb bb Genotypes: BB 0 % ______ 50 % ______ Bb 50 % ______ 50 % Small Beaks ______ Bb 50 % ______ Phenotypes: Big Beaks 3) Heterozygous ( Bb ) x Heterozygous ( Bb ) B Genotypes: b B BB Bb b Bb bb BB 25 % ______ 25 % ______ Bb 50 % ______ 75 % Small Beaks ______ Bb 25 % ______ Phenotypes: Big Beaks Review: B and b What were all the alleles used above? ____________________________________________________ 3 How many possible genotypes do you expect to find within this species, for beak size? _____________
