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Ch. 5 - Genetic Linkage and Mapping in Eukaryotes
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
Sanders3rd EditionGenetic Analysis: An Integrated ApproachISBN: 9780135564172Not the one you use?Change textbook
All textbooksSanders 3rd EditionCh. 5 - Genetic Linkage and Mapping in EukaryotesProblem 21b
Chapter 5, Problem 21b

Gene R and gene T are genetically linked. Answer the following questions concerning a dihybrid organism with the genotype Rt/rT:


If two crossover events occur between these two genes, what are the genotypes of the recombinant chromosomes?

Verified step by step guidance
1
Understand that genetic linkage means that genes R and T are located close to each other on the same chromosome, and their inheritance is not completely independent.
Recognize that the genotype Rt/rT indicates that the organism is heterozygous for both genes, with one chromosome carrying the alleles R and t, and the other chromosome carrying the alleles r and T.
Recall that a double crossover event involves two separate crossover events occurring between the two linked genes, effectively swapping the alleles between the homologous chromosomes twice.
Determine the recombinant chromosomes by analyzing the effect of the double crossover. The first crossover will exchange alleles between the homologous chromosomes, and the second crossover will reverse the exchange, resulting in recombinant chromosomes with the genotypes RT and rt.
Conclude that the recombinant chromosomes resulting from two crossover events are RT and rt, as these are the new combinations of alleles formed after the double crossover process.

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Key Concepts

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

Genetic Linkage

Genetic linkage refers to the tendency of genes located close to each other on the same chromosome to be inherited together during meiosis. This occurs because linked genes are less likely to be separated by recombination events, which can shuffle alleles between homologous chromosomes. Understanding linkage is crucial for predicting the inheritance patterns of traits controlled by these genes.
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Chi Square and Linkage

Crossover Events

Crossover events occur during meiosis when homologous chromosomes exchange segments of genetic material. This process results in new combinations of alleles, leading to genetic diversity in gametes. In the context of linked genes, the number and location of crossover events can significantly affect the genotypes of the resulting recombinant chromosomes.
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Multiple Cross Overs and Interference

Recombinant Genotypes

Recombinant genotypes are the genetic combinations that arise from crossover events between linked genes. When two crossover events occur, they can produce chromosomes that carry different combinations of alleles than the parental types. Identifying these recombinant genotypes is essential for understanding the genetic variation and inheritance patterns in offspring.
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Related Practice
Textbook Question

Genetic linkage mapping for a large number of families identifies 4% recombination between the genes for Rh blood type and elliptocytosis (see Problem 18). At the Rh locus, alleles R and r control Rh+ and Rh- blood types. Allele E producing elliptocytosis is dominant to the wild-type recessive allele e. Tom and Terri each have elliptocytosis, and each is . Tom's mother has elliptocytosis and is Rh- while his father is healthy and has Rh+. Terri's father is Rh+ and has elliptocytosis; Terri's mother is Rh- and is healthy.


What is the probability that a child of Tom and Terri who is Rh+ will have elliptocytosis?

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Textbook Question

A group of families in which an autosomal dominant condition is present are studied to determine lod scores for possible genetic linkage between three RFLP markers (R1, R2, and R3) and the disease gene. The chart shows lod scores at each of the recombination distances (θ values) tested. Provide an interpretation of the lod score results for each RFLP. Be specific about any significant evidence of genetic linkage.

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Textbook Question

Gene R and gene T are genetically linked. Answer the following questions concerning a dihybrid organism with the genotype Rt/rT:


If r = 0.20, give the expected frequencies of gametes produced by the dihybrid.

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Textbook Question

Gene R and gene T are genetically linked. Answer the following questions concerning a dihybrid organism with the genotype Rt/rT:


Can you make a general statement about how the occurrence of two crossover events between a given pair of linked genes affects the estimate of recombination frequency?

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Textbook Question

T. H. Morgan's data on eye color and wing form genetic linkage between the two genes. Test the genetic linkage (shown in the figure below) data with chi-square analysis, and show that the results are significantly different from the expectation under the assumption of independent assortment.

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Textbook Question

A wild-type trihybrid soybean plant is crossed to a pure-breeding soybean plant with the recessive phenotypes pale leaf (l), oval seed (r), and short height (t). The results of the three-point test cross are shown below. Traits not listed are wild type.

What are the alleles on each homologous chromosome of the parental wild-type trihybrid soybean plant? Place the alleles in their correct gene order. Use L, R, and T to represent dominant alleles and l, r, and t for recessive alleles.

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