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Eye Color Genetics ProjectStudent #1 & Student #2

1st Period BiologyMr. Teacher

Student #1 – blue eyes

Father – blue eyes Mother – green eyes

Paternal Grandparents

Grandfather –green eyes

Grandmother –blue eyes

Maternal Grandparents

Grandmother –green eyes

Grandfather –brown eyes

Punnett Square for Student #1Student #1’s Mother has allele combination bbGG and Father has bbgg.

Brown/Blue b bb bb bbb bb bb

Green/Hazel G Gg Gg Ggg 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.

Father – brown eyes

Paternal Grandparents Maternal Grandparents

Mother – blue eyes

Student #2 – brown eyes

Grandmother – hazel eyes

Grandfather – blue eyes

Grandmother – brown eyes

Grandfather – brown eyes

Punnett Square for Student #2Student #2’s Mother has allele combination bbgg and Father has BBGG.

Brown/Blue b bB Bb BbB Bb Bb

Green/Hazel g gG Gg GgG 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 browneyes.

Punnett Square for Potential OffspringStudent #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 bB BB Bbb Bb bb

Green/Hazel g gG Gg Ggg 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 OffspringSee the possible combinations of the two genes (brown/blue, green/hazel):

Brown/Blue B bB BB Bbb Bb bb

Green/Hazel g gG Gg Ggg 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 GenotypesThe 4 brown/blue genes we paired are BB, Bb, Bb, and

bb. These were taken from the Punnett Square.

Number of Genotypes = 16BBGg = 2, BBgg = 2, BbGg = 4, Bbgg = 4, bbGg = 2,

bbgg = 2

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

Genotype ProbabilitiesNumber of Genotypes = 16

BBGg = 2, BBgg = 2, BbGg = 4, Bbgg = 4, bbGg = 2, bbgg = 2

Probability of BBGg offspring = 2/16 * 100 = 12.5%

Probability of BBgg offspring = 2/16 * 100 = 12.5%

Probability of BbGg offspring = 4/16 * 100 = 25%Probability of Bbgg offspring = 4/16 * 100 = 25%Probability of bbGg offsrping = 2/16 * 100 =

12.5%Probatility of bbgg offspring= 2/16 * 100 = 12.5%

Total 100%

Brown Phenotype ProbabilityThere 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 ProbabilityFor 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.