Question

Drosophila flies have red eyes. Mutations in various genes cause change in eye color. Brown eye color is caused by a recessive mutation (B > b) Scarlet eye color is caused by another recessive mutation in a gene located on a different chromosome (A > a) Flies with genotypes A-B- are red-eyed (wild-type). However, double recessive homozygotes (aabb) are white-eyed (epistatic gene interaction with no pigment produced; recall teh case of chicken combs) Cross a true-breeding wild type female to a white-eyed male of the genotype aabb. Then cross a F1 female to another white-eyed male of the genotype aabb. What are phenotypes and their expected ratios for the F2 resulting from this cross? 50% red, 50 % scarlet 25% red, 50 % scarlet, 25 % white 25% red, 25 % scarlet, 25 % white, 25 % brown 50% brown, 50 % scarlet 56.25% red, 18.75 % scarlet, 18.75 % brown, 6.25 % white

          Drosophila flies
have red eyes. Mutations in various
genes cause change in eye color.
 Brown eye color is caused by a
recessive mutation (B > b)
Scarlet eye color is caused by another
recessive mutation in a gene located on a different
chromosome (A > a)
Flies with genotypes A-B- are
red-eyed (wild-type).
However, double recessive homozygotes
(aabb) are white-eyed
(epistatic gene interaction with no
pigment produced; recall teh case of chicken
combs)
Cross a true-breeding wild
type female to
a white-eyed male of the
genotype aabb.
Then cross a F1 female to
another  white-eyed male of the
genotype aabb.   
What are phenotypes and their expected ratios for
 the F2 resulting
from this cross?
50% red, 50 % scarlet
25% red, 50 % scarlet, 25 % white
25% red, 25 % scarlet, 25 % white, 25 % brown
50% brown, 50 % scarlet
56.25% red, 18.75 % scarlet, 18.75 % brown, 6.25 % white

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Added by Roberto S.

Biology for AP Courses

Julianne Zedalis, John Eggebrecht

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Solved by Expert Jenny Wu

07/12/2023

Step 1

The F1 generation will all be heterozygous for both genes (AaBb). Now, we cross an F1 female (AaBb) with another white-eyed male (aabb). We can use a Punnett square to determine the genotypes and phenotypes of the F2 generation. The F1 female can produce the Show more…

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Drosophila flies have red eyes. Mutations in various genes cause change in eye color. Brown eye color is caused by a recessive mutation (B > b) Scarlet eye color is caused by another recessive mutation in a gene located on a different chromosome (A > a) Flies with genotypes A-B- are red-eyed (wild-type). However, double recessive homozygotes (aabb) are white-eyed (epistatic gene interaction with no pigment produced; recall teh case of chicken combs) Cross a true-breeding wild type female to a white-eyed male of the genotype aabb. Then cross a F1 female to another white-eyed male of the genotype aabb. What are phenotypes and their expected ratios for the F2 resulting from this cross? 50% red, 50 % scarlet 25% red, 50 % scarlet, 25 % white 25% red, 25 % scarlet, 25 % white, 25 % brown 50% brown, 50 % scarlet 56.25% red, 18.75 % scarlet, 18.75 % brown, 6.25 % white

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Transcript

00:01 Drosophila have red eyes.

00:03 Mutation in various gene cause a change in eye color.

00:06 Brown color is caused by a recessive mutation.

00:11 So obviously, capital b is, i guess, a wild type and then brown is a recessive.

00:20 Now, scarlet eye color is caused by another recessive mutation in a gene located on different chromosome.

00:26 So again, capital a is wild type and lower a is scarlet recessive.

00:32 Fly with genotype, capital a and capital b are red eye wild type.

00:36 However, double recessive homodigus, homodigus lower a and b are white eye.

00:44 Epistatic gene interaction with no pigment produced.

00:51 Recall the case of chicken combs.

00:54 Cross a true breeding wild type female to a white eye male of the genotype.

01:01 Homodigus lower a and b.

01:03 Then cross f1 female to another white eye male of the same genotype.

01:09 What are the phenotypes and their expected ratio of f2? so let's take a look at the parent.

01:16 So the parent, a true breed wild type female.

01:23 So homodigus capital a and b crossed with homodigus lower a and lower b.

01:32 So this is white.

01:33 Now, we get our f1.

01:39 F1 pick up one allele from each of the parent, heterozygous a and heterozygous b.

01:46 So with both capital a and capital b, it's going to be a wild type.

01:52 So let's say you cross f1 fly with another male of homozygous a and b, lowercase.

02:04 So double recessive...

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