Chapter 7: Problem 25
Are sister chromatid exchanges effective in producing genetic variability in an individual? in the offspring of individuals?
Chapter 7: Problem 25
Are sister chromatid exchanges effective in producing genetic variability in an individual? in the offspring of individuals?
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Get started for freeDescribe the cytological observation that suggests that crossing over occurs during the first meiotic prophase.
Review the Chapter Concepts list on p. \(121 .\) Most of these center on the process of crossing over between linked genes. Write a short essay that discusses how crossing over can be detected and how the resultant data provide the basis of chromosome mapping.
In Drosophila, a cross was made between females expressing the three X-linked recessive traits, scute bristles \((s c),\) sable body \((s)\) and vermilion eyes ( \(v\) ), and wild-type males. All females were wild type in the \(F_{1},\) while all males expressed all three mutant traits. The cross was carried to the \(\mathrm{F}_{2}\) generation and 1000 offspring were counted, with the results shown in the following table. No determination of sex was made in the \(\mathrm{F}_{2}\) data. (a) Using proper nomenclature, determine the genotypes of the \(P_{1}\) and \(F_{1}\) parents. (b) Determine the sequence of the three genes and the map distance between them. (c) Are there more or fewer double crossovers than expected? (d) Calculate the coefficient of coincidence; does this represent positive or negative interference?
The genes dumpy wings \((d p),\) clot eyes \((c l),\) and apterous wings \((a p)\) are linked on chromosome II of Drosophila. In a series of twopoint mapping crosses, the genetic distances shown below were determined. What is the sequence of the three genes?
Why is a 50 percent recovery of single-crossover products the upper limit, even when crossing over always occurs between two linked genes?
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