Chapter 6: Problem 16
Describe the unique features of ascomycetes that lend themselves to genetic analysis.
Chapter 6: Problem 16
Describe the unique features of ascomycetes that lend themselves to genetic analysis.
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Get started for freeResearchers have discovered that some regions of chromosomes are much more likely than others to cross over. We might call such a region a "hot spot" for crossing over. Let's suppose that two genes, gene \(A\) and gene \(B\), are \(5,000,000 \mathrm{bp}\) apart on the same chromosome. Genes \(A\) and \(B\) are in a hot spot for crossing over. Two other genes, let's call them gene \(C\) and gene \(D\), are also \(5,000,000 \mathrm{bp}\) apart but are not in a hot spot for recombination. If we conducted two-factor crosses to compute the map distance between genes \(A\) and \(B\) and other two-factor crosses to compute the map distance between genes \(C\) and \(D\), would the calculated map distance between \(A\) and \(B\) be the same as that between \(C\) and \(D\) ? Explain.
What is mitotic recombination? A heterozygous individual \((B b)\) with brown eyes has one eye with a small patch of blue. Provide two or more explanations for how the blue patch may have occurred.
When true-breeding mice with brown fur and short tails (BBtt) were crossed to true-breeding mice with white fur and long tails (bbTT), all of the \(\mathrm{F}_{1}\) offspring had brown fur and long tails. The \(\mathrm{F}_{1}\) offspring were crossed to mice with white fur and short tails. What are the possible phenotypes of the \(\mathrm{F}_{2}\) offspring? Which \(\mathrm{F}_{2}\) offspring are recombinant, and which are nonrecombinant? What are the ratios of phenotypes of the \(\mathrm{F}_{2}\) offspring if independent assortment is taking place? How are the ratios affected by linkage?
In most two-factor crosses involving linked genes, we cannot tell if a double crossover between the two genes has occurred because the offspring will inherit the nonrecombinant pattern of alleles. How does the inability to detect double crossovers affect the calculation of map distance? Is map distance underestimated or overestimated because of our inability to detect double crossovers? Explain your answer.
If you try to throw a basketball into a basket, the likelihood of succeeding depends on the size of the basket. It is more likely that you will get the ball into the basket if the basket is bigger. In your own words, explain how this analogy applies to the idea that the likelihood of crossing over is greater when two genes are far apart than when they are close together.
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