You are trying to create your original unknown fly phenotype

You are trying to create your original unknown fly phenotype that has white eyes and no mutant phenotype. You know that the mutant phenotype, white eyes, is x-linked recessive. You only have two surviving flies, a female with phenotype Curly Dicheate White Eyes, and a male with the phenotype Curly Dichaete wild-type eyes.

1. What are the genotypes of your starting male and female flies?

2. List the possible phenotypes that may result from crossing flies and give the probability of each.

3. How many flies do you need to collect to have a 99% chance of getting at least one fly with your desired phenotype?

Solution

1. female with phenotype white eyes Xw Xw, homozygous recessive

male with wild-type eyes Xw+Y, hemizygous dominant.

w is white eye; w+ is red eyed

2. Xw Xw x   Xw+Y

the possible phenotypes are females with wild-type eyes and males with white eyes in 1:1 ratio

probability is 50% for each phenotype

in F2 generation

it is 1:1:1:1 ratio, one female with white eyes, one male with white eyes. one female with wildtype eyes and one male with wild type eyes.

each has a probability of 25%.

3. N=loge(1-P)/loge(1-f) where N is number of flies to be collected, p is probability or chance of success, f is frequency of events.

as frequency is 0.25 in f2 generation for a homozygous gene. for two genes it is 0.25x0.25=0.0625

N=log(1-0.99)/log(1-0.0625)=71.35.

so probably a minimum of 72 individuals are to be collected to get the desired phenotype.

Note. i have no idea how to create a white eye phenotype without mutant. please check that.