A diploid cell contains three pairs of homologous chromosomes des...

Question

A diploid cell contains three pairs of homologous chromosomes designated C1 and C2, M1 and M2, and S1 and S2. No crossing over occurs. What combinations of chromosomes are possible in (a) daughter cells following mitosis, (b) cells undergoing the first meiotic metaphase, (c) haploid cells following both divisions of meiosis?

Accepted Answer

Hi everyone. Let's look at our next question. It says, what does it imply if the recombination frequency is 50%. Well let's think about what recombination frequency is. We can recall that. We calculate it by dividing the number of recombinant offspring by the total number of offspring times 100%. So when our recombination frequency is 50 Divide both sides by 100%. We know that one half of the offspring are recombinant because the number of recombinant offspring over the total number will equal one half. Now let's think if the two genes were very close together, crossing over never occurs. They always move together. In that situation we would have no recombinant offspring whatsoever. And so this recombination frequency would be zero. So from zero to let's think of the other situation where they are in completely separate chromosomes and independently assort. So we're going to imagine this an individual who's hetero ziggy's for two different genes that are on two different chromosomes. That a sword completely independently. And we're going to imagine that this individual was the product of a cross between parents that were homos I guess dominant and recessive for these genes. So you can tell right away which um gametes were from which parent. Well if these genes independently assort they're completely separate chromosomes, this had this individual can produce four types of gabby's. They can produce both genes being dominant, one being dominant, one being recessive, the other combination and both being recessive. These two genes here are the parental types, they would be inherited together um from the paternal or maternal chromosomes But these two here are in a different combination from the parent. These are recumbent. So when we look at this we would see that 50% of the offspring would have the recombinant Genotype and 50% parental. So 50% recombination frequency means the genes independently assort say independent assortment Equals 50% recombination frequency. So with that in mind, let's look at our answer choices. Choice A says the genes are very close to each other. Well we know this is incorrect because when the jeans are very close, our recombination frequency is zero. Since we get no recombination offsprings. Choice B says the two genes may be located on different chromosomes. Well this is correct Because 50% recombination frequency means essentially these two genes are independently a sorting choice C. Says there are too many genes in the chromosomes that doesn't really apply to our situation as it doesn't have any um impact on recombination frequency. And then Choice D. There is no genetic variation within the population. Um Well that's not correct because we're seeing recumbent offspring with a wide variety of different Jenna types here. So Choice D. Is not correct. So again, what does it imply if the recombination frequency is 50% choice be the two genes may be located on different chromosomes in the next video

Key Concepts

Diploid and Haploid Cells

Mitosis vs. Meiosis

Homologous Chromosomes

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