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Ch. 5 - Chromosome Mapping in Eukaryotes
All textbooksKlug 12th EditionCh. 5 - Chromosome Mapping in EukaryotesProblem 23
Chapter 5, Problem 23

Based on our discussion of the potential inaccuracy of mapping (see Figure 5.12), would you revise your answer to Problem 22? If so, how?

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1
Review Problem 22 to understand the original mapping and the genetic distances involved.
Examine Figure 5.12 to identify the potential sources of inaccuracy in genetic mapping, such as interference, double crossovers, or incorrect assumptions about recombination frequency.
Consider how these inaccuracies might affect the genetic distances or order of genes in the original map from Problem 22.
Determine if the inaccuracies suggest a need to adjust the genetic distances or reorder the genes to better reflect the true genetic map.
Propose a revised genetic map or explanation, taking into account the potential inaccuracies identified in Figure 5.12.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Genetic Mapping

Genetic mapping is the process of determining the location and distance between genes on a chromosome. It involves using markers to identify the relative positions of genes, which can help in understanding inheritance patterns and genetic linkage. Inaccuracies in mapping can arise from recombination events or limitations in the resolution of the mapping techniques used.
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Mapping Overview

Linkage Disequilibrium

Linkage disequilibrium refers to the non-random association of alleles at different loci. It occurs when certain combinations of alleles are inherited together more frequently than would be expected by chance. Understanding linkage disequilibrium is crucial for interpreting genetic maps, as it can affect the accuracy of gene location predictions and the relationships between traits.
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Chi Square and Linkage

Recombination Frequency

Recombination frequency is a measure of how often recombination occurs between two genes during meiosis. It is used to estimate the distance between genes on a chromosome, with higher frequencies indicating greater distances. Variability in recombination rates can lead to inaccuracies in genetic mapping, making it essential to consider when revising answers based on mapping data.
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Recombination after Single Strand Breaks
Related Practice
Textbook Question
An organism of the genotype AaBbCc was testcrossed to a triply recessive organism (aabbcc). The genotypes of the progeny are presented in the following table. 20 AaBbCc 20 AaBbcc 20 aabbCc 20 aabbcc 5 AabbCc 5 Aabbcc 5 aaBbCc 5 aaBbcc If these three genes were all assorting independently, how many genotypic and phenotypic classes would result in the offspring, and in what proportion, assuming simple dominance and recessiveness in each gene pair?
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Textbook Question
An organism of the genotype AaBbCc was testcrossed to a triply recessive organism (aabbcc). The genotypes of the progeny are presented in the following table. 20 AaBbCc 20 AaBbcc 20 aabbCc 20 aabbcc 5 AabbCc 5 Aabbcc 5 aaBbCc 5 aaBbcc Answer part (a) again, assuming the three genes are so tightly linked on a single chromosome that no crossover gametes were recovered in the sample of offspring.

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Textbook Question
An organism of the genotype AaBbCc was testcrossed to a triply recessive organism (aabbcc). The genotypes of the progeny are presented in the following table. 20 AaBbCc 20 AaBbcc 20 aabbCc 20 aabbcc 5 AabbCc 5 Aabbcc 5 aaBbCc 5 aaBbcc What can you conclude from the actual data about the location of the three genes in relation to one another?

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Textbook Question
How do we know that in humans the X chromosomes play no role in human sex determination, while the Y chromosome causes maleness and its absence causes femaleness? Why are many expected crossover phenotypes missing? Can any of these loci be mapped from the data given here? If so, determine map distances.
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Textbook Question
Traditional gene mapping has been applied successfully to a variety of organisms including yeast, fungi, maize, and Drosophila. However, human gene mapping has only recently shared a similar spotlight. What factors have delayed the application of traditional gene-mapping techniques in humans?
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Textbook Question
In a certain plant, fruit is either red or yellow, and fruit shape is either oval or long. Red and oval are the dominant traits. Two plants, both heterozygous for these traits, were testcrossed, with the following results. Determine the location of the genes relative to one another and the genotypes of the two parental plants.
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