A Drosophila experiment examining potential genetic linkage of X-...

Question

A Drosophila experiment examining potential genetic linkage of X-linked genes studies a recessive eye mutant (echinus), a recessive wing-vein mutation (crossveinless), and a recessive bristle mutation (scute). The wild-type phenotypes are dominant. Trihybrid wild-type females (all have the same genotype) are crossed to hemizygous males displaying the three recessive phenotypes. Among the 20,765 progeny produced from these crosses are the phenotypes and numbers listed in the table. Any phenotype not given is wild type.

Phenotype Number
1. Echinus     8576
2. Scute       977
3. Crossveinless        716
4. Echinus, scute       681
5. Scute, crossveinless     8808
6. Scute, crossveinless, echinus         4
7. Echinus, crossveinless     1002
8. Wild type         1
20,765

Calculate the recombination frequencies between each of the gene pairs.

Accepted Answer

Hello, everyone and welcome to today's video. So today we have a very long problem which may seem harder than it actually is. Let's jump straight into it though. We have that A P plan experiment is conducted to study genetic linkage of two genes which are the flower color that is given by the capitalized W for white color or lower case W for purple color. And this is between parentheses N C shape which is capitalized R for round or lowercase R for wrinkled and this is also between parenthesis. Now, Diridon which are heterozygous for W and heterozygous for R are cross with homozygosis plants which are homozygous recessive for both W and R to produce 1000 offspring. So this is going to be your total number of offspring producing the F1 generation. So, among the offspring, 470 have the dominant phenotype for both traits. 30 have the recessive phenotype for both traits. 242 have the dominant phenotype for flower color. But the recessive phenotype for seed shape and 258 have the dominant phenotype for seed shape. But the recessive phenotype for flower color So what is the real combination frequency between the genes associated with C shape and flower color? Well, as answer choice A, we have 50% as answer choice B, we have 47% as answer choice C, we have 24.2%. And as answer choice D we have 3%. Well, remember that the formula for the recombination frequency in this type of process is going to be equal to the number of recombinant divided by a total number of offspring times 100%. All we have to do really is go into the problem and determine the number of recombinant for these seed shape and flower color traits, which is going to be 242 that are stated to have the dominant phenotype for flower color. But the recessive one for phenotype of the seed shape. So that is the number that we're going to put on top. Now, we're told that 1000 offspring is the total number of offspring. So we're going to be putting that at the bottom of the fraction, which is what we have just on the screen. Now, we have a fraction of 242 over 1000. And then we multiply this by 100% and this is going to be equal to 24 .2%. And this is going to be a combination frequency. Now, because of this, the correct answer choice is going to be C24.2%. I really hope this video helped you and I hope to see you on the next one.

Key Concepts

Genetic Linkage

Recombination Frequency

Phenotypic Ratios

Watch next