In Drosophila, two mutations, Stubble (Sb) and curled (cu), are l...

Question

In Drosophila, two mutations, Stubble (Sb) and curled (cu), are linked on chromosome III. Stubble is a dominant gene that is lethal in a homozygous state, and curled is a recessive gene. If a female of the genotype

is to be mated to detect recombinants among her offspring, what male genotype would you choose as a mate?

Accepted Answer

Hi everyone. Welcome back. Let's look at our next problem here. It says if you want to detect recombinant offspring in Drosophila, what should the jena types of the female and male parents be? Well let's think about how we look to see whether we have a competent offspring. And we start with a theoretical example where we have jean B. And Jeannie on the same chromosome. And we start with the idea that if there's no recombination there's no crossing over. Here's one chromosome in the other chromosome. 50% of the gametes here will be big, be big E. And 50% little B. Little E. So 50% homogeneous dominant. 50% homos I guess recessive. If you crossed um this parent, this hetero sex parent with a homesickness recessive parent, you're going to have 50% of the offspring showing the dominant traits to dominant traits, Big B. And Big E. 50% of the offspring will show two recessive traits since there's no recombination and they're getting past together. So when there's recombination you'll see some percent of the offspring and again in a test cross with the homicide is recessive. Um be showing one dominant trait and one recessive. And that's because when it's crossing over that allows you to also have gametes that are for instance Bigby little E. Or little B. Biggie. When you cross them with a homogeneous recessive other parent. Um You can tell by whether the offspring carries the dominant or recessive trait whether the gamut they received what it was. So um we definitely want to use a hetero zegas parent in the trait of interest crossed with a homogeneous recessive parent. Now we see here in our answer questions that we've got a choice of female and male, where here's where it's important for us to recall that in Drosophila crossing over occurs only and females. So we would definitely have our heterocyclic parent being female because we're studying when recombination occurs. So it would be useless to have a hetero male since there will be no crossing over that won't tell us anything. So we want our female to be heterocyclic and our mail to be homesick is recessive. And we see that here in answer choice B female heterosexual. Male homosexuals recessive. So let's just look briefly at our other answer choices choice A says female. Six male hetero sickness. Again, the hetero hetero zig across as a dye hybrid cross and would automatically give us, even if they were independently independently. A sorting would give us this 1 to 2 to one ratio of different offspring. And what we're looking for is a simple way to check um how did the alleles recombine and the cross with the whole process of parent lets us automatically deduce what the gamut was that the offspring received choice. They wouldn't be useful choice. C says female homesickness recessive. Male hetero sickness. Well, again, we're looking for when this crossover occur and males do not have crossover events. So having a male hetero ziggy where we'd be looking for the crossing over events doesn't help us choice. D says female homosexuals recessive. Male homosexuals recessive. That wouldn't tell us anything because in both parents can only generate gametes that our home is a recessive for both treats. So that wouldn't tell us anything. So, again, if you want to detect competent offspring in Drosophila, which is the genotype of the female and male parents, be choice be female heterosexual. Male homosexuals recessive. See you in the next video.

Key Concepts

Gene Linkage

Dominant and Recessive Alleles

Homozygosity and Lethality

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