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Ch. 13 - Meiosis and Sexual Life Cycles

Chapter 13, Problem 6c

DRAW IT The diagram shows a cell in meiosis.

Diagram illustrating chromosomes during Meiosis I, showing homologous pairs and crossing over.

c. Identify the stage of meiosis shown.

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Welcome back everyone. Let's look at our next problem. During the recombination. In the pro face stage DNA sequences are broken and then rejoined, identify which of the genetic recombination will occur after the crossing over of the given homologous pair. So here we see our pair of homologous chromosomes, say paternal and maternal. And we see in this spot, right here on the inner legs where they were next to each other in our arms, the lower arms you have a crossing over point. So what we'd expect to see is at this point right here on the lower parts of these arms, below the crossing over point. We're going to see an exchange of that piece of chromosome and we'll see that swapped. So now I'm going to scroll down just to show us all of our answer choices here so we can evaluate them. So this gives us four possibilities for what the chromosomes will look like after that crossing over. So let's look at choice A choice A shows the outer arms of the lower part of these two chromosomes with the piece swapped, but it's the inner arms that that have crossed over. So choice A is not correct. Now let's take a choice B. Choice B does show we're on the inner arms were down on the lower arms. And we see that yes, that lower portion there below the crossover point has swapped. Now the two chromosomes each have a little bit of the homologous chromosome from the other parent. So Choice B does correctly show what has happened and what those chromosomes look like after recombination. But let's just take a look at our other choices just to see why they are not correct. We see choice. See here, Choice C. Has the swapped portion occurring above the crossing over point, but that is not correct. It's down below the crossover point or more outer. If the crossing over point, we're up here, the crossover portion would be above. So further away from the center mears is where that those pieces swap. Then Choice D. Indeed shows at the end of the arms correctly, but it's chosen on the upper arms of that pair. So Choice D. Is incorrect. So again, our correct answer is Choice B. For representing what those chromosomes will look like after recombination. See you in the next video.
Related Practice
Textbook Question

If we continue to follow the cell lineage from question 4, then the DNA content of a single cell at metaphase of meiosis II will be a. 0.25x. b. 0.5x. c. x. d. 2x.

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Textbook Question

DRAW IT The diagram shows a cell in meiosis. a. Label the appropriate structures with these terms: chromosome (label as duplicated or unduplicated), centromere, kinetochore, sister chromatids, nonsister chromatids, homologous pair (use a bracket when labeling), homolog (label each one), chiasma, sister chromatid cohesion, and gene loci, labeling the alleles of the F and H genes.

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Textbook Question

DRAW IT The diagram shows a cell in meiosis. b. Describe the makeup of a haploid set and a diploid set.

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Textbook Question

Assume that genes A and B are on the same chromosome and are 50 map units apart. An animal heterozygous at both loci is crossed with one that is homozygous recessive at both loci. What percentage of the offspring will show recombinant phenotypes resulting from crossovers? Without knowing these genes are on the same chromosome, how would you interpret the results of this cross?

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Textbook Question

Two genes of a flower, one controlling blue (B) versus white (b) petals and the other controlling round (R) versus oval (r) stamens, are linked and are 10 map units apart. You cross a homozygous blue oval plant with a homozygous white round plant. The resulting F1 progeny are crossed with homozygous white oval plants, and 1,000 offspring plants are obtained. How many plants of each of the four phenotypes do you expect?

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Textbook Question

You design Drosophila crosses to provide recombination data for gene a, which is located on the chromosome shown in Figure 15.12. Gene a has recombination frequencies of 14% with the vestigial wing locus and 26% with the brown eye locus. Approximately where is a located along the chromosome?

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