Student #1 & Student #2 1st Period Biology Mr. Teacher Student #1 – blue eyes Father – blue eyes Paternal Grandparents Grandfather – green eyes Grandmother – blue eyes Mother – green eyes Maternal Grandparents Grandfather – brown eyes Grandmother – green eyes Punnett Square for Student #1 Student #1’s Mother has allele combination bbGG and Father has bbgg. Brown/Blue b b b bb bb b bb bb Green/Hazel G G g Gg Gg g Gg Gg So the offspring (Student #1) is bbGg, which should result in hazel eyes. However, the green/hazel gene has incomplete dominance. This means that the expressed phenotype can be anywhere from pure green to dark hazel depending on the genes given by the parents. Student #2 – brown eyes Father – brown eyes Paternal Grandparents Grandfather – brown eyes Grandmother – brown eyes Mother – blue eyes Maternal Grandparents Grandfather – blue eyes Grandmother – hazel eyes Punnett Square for Student #2 Student #2’s Mother has allele combination bbgg and Father has BBGG. Brown/Blue b b B Bb Bb B Bb Bb Green/Hazel g g G Gg Gg G Gg Gg So the offspring (Student #2) is BbGg, which results in brown eyes. The dominant phenotype here is brown eyes, as every possible combination results in brown eyes. Punnett Square for Potential Offspring Student #1’s allele combination is bbgg, and Student #2’s allele combination is BbGg. Here is the Punnett Square, and the various combinations follow: Brown/Blue B b B BB Bb b Bb bb Green/Hazel g g G Gg Gg g gg gg Student #1 is homozygous in their gene makeup. Both alleles for each genes are the same (bb and gg). Student #2 is heterozygous in their gene makeup. Student #2 posseses both alleles for each gene (Bb and Gg). Punnett Square for Potential Offspring See the possible combinations of the two genes (brown/blue, green/hazel): Brown/Blue B b B BB Bb b Bb bb Green/Hazel g g G Gg Gg g gg gg Each brown/blue gene can be paired up with 4 different green/hazel genes. This is repeated with each brown/blue gene. Therefore there are 16 different gene pairs. These are listed on the next slide. Possible Genotypes The 4 brown/blue genes we paired are BB, Bb, Bb, and bb. These were taken from the Punnett Square. Brown/Blue Gene Possible Pairs with Green/Hazel BB pair BBGg, BBGg, BBgg, BBgg Bb pair (first) BbGg, BbGg, Bbgg, Bbgg Bb pair (second) BbGg, BbGg, Bbgg, Bbgg bb pair bbGg, bbGg, bbgg, bbgg Number of Genotypes = 16 BBGg = 2, BBgg = 2, BbGg = 4, Bbgg = 4, bbGg = 2, bbgg = 2 Genotype Probabilities Number of Genotypes = 16 BBGg = 2, BBgg = 2, BbGg = 4, Bbgg = 4, bbGg = 2, bbgg = 2 Probability of BBGg offspring = Probability of BBgg offspring = Probability of BbGg offspring = Probability of Bbgg offspring = Probability of bbGg offsrping = Probatility of bbgg offspring = Total 2/16 * 100 = 12.5% 2/16 * 100 = 12.5% 4/16 * 100 = 25% 4/16 * 100 = 25% 2/16 * 100 = 12.5% 2/16 * 100 = 12.5% 100% Brown Phenotype Probability There are 4 genotypes that produce a brown eyed offspring: • BBGg, BBgg, BbGg, Bbgg Since brown is dominant over all other colors the presence of a big B allele will automatically give the child brown eyes, regardless of the green/blue gene. Adding the probabilities for each of the genotypes we get the total probability for the phenotype • 12.5% + 12.5% + 25% + 25% = 75% probability of having a brown eyed offspring Hazel Phenotype Probability For the green/hazel gene to be shown in a phenotype the brown/blue gene must be bb. There is one genotype that will give you hazel eyes. Because the gene for green/hazel eyes has incomplete dominance you need a heterozygous genotype for green/hazel to have hazel eyes. • bbGg Since there is only one genotype for hazel eyes, the probability for the phenotype is the same as the probability for the genotype. • bbGg = 12.5% probability of having a hazel eyed offspring Green Phenotype Probability The green phenotype requires a genotype of bbGG. Since this genotype is not represented in our hypothetical offspring, the probability of green phenotype is 0%. Blue Phenotype Probability The only genotype that produces a blue phenotype is bbgg. Because of this the probability of the genotype is the same as the probability of the phenotype. 12.5% probability child will have blue eyes. Conclusion! It is most probable that if Student #1 and Student #2 were to create an offspring, that offspring would have the phenotype of brown eyes. It is impossible for their offspring to have green eyes.