Probability and Genetics

Fruit Fly Color and Probability

Fruit Flies

The body color in fruit flies is controlled by two alleles– Grey is dominant and represented by G– Black is recessive and represented by g

The phenotypes of the flies follow the chart below.

Phenotype(color)

Grey Black

Genotype (gene makeup)

GG, Gg gg

Sample Punnett Square 1

Cross a homozygous grey fly (GG) with a homozygous black fly (gg)

Sample Punnett Square 1

All offspring are phenotype grey and genotype Gg

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So 4 out of 4 possible outcomes have genotype Gg and phenotype grey

There is a 100% possibility that the offspring will be Grey (Gg)

Sample Punnett Square 2

Cross a heterozygous grey fly (Gg) with a homozygous black fly (gg).

Sample Punnett Square 1

Offspring have two possibilities in this case

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Grey (Gg) Black (gg) Each outcomes happens 2 times

out of 4 = 50% chance

Sample Punnett Square 3

Cross two heterozygous grey flies (Gg)

Grey (Gg or GG) Black (gg) First explore phenotypes

– Grey happens 3 out of 4 times = 75%– Black happens 1 out of 4 times = 25%

There is a 75% possibility the offspring will be grey and a 25% possibility they will be black.

Sample Punnett Square 3

Offspring have several possibilities in this case

Gg happens 2 out of 4 times = 50% GG happens 1 out 4 times = 25% gg happens 1 out of 4 times = 25%

For the whole example:– 25% chance of Black (gg) flies– 25% chance of Grey (GG) flies– 50% chance of Grey (Gg) flies

Sample Punnett Square 3

Now let’s explore the probability of genotypes

Probability

The concept of probability and genetics goes outside of just flies

For your project you will analyze the probability for eye color

Use the same techniques used for flies