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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 28b
Chapter 5, Problem 28b

Neurofibromatosis 1 (NF1) is an autosomal dominant disorder inherited on human chromosome 17. Part of the analysis mapping the NF1 gene to chromosome 17 came from genetic linkage studies testing segregation of NF1 and DNA genetic markers on various chromosomes. A DNA marker with two alleles, designated 1 and 2, is linked to NF1. The pedigree below shows segregation of NF1 (darkened symbols) and gives genotypes for the DNA marker for each family member.
Pedigree chart showing NF1 gene segregation with genotypes for DNA markers across three generations.
Based on the phase of alleles on chromosomes in generation II, is there any evidence of recombination among the eight offspring in generation III? Explain.

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Step 1: Understand the problem. Neurofibromatosis 1 (NF1) is an autosomal dominant disorder linked to a DNA marker with two alleles (1 and 2). The goal is to determine if recombination occurred among the eight offspring in generation III based on the phase of alleles in generation II.
Step 2: Define key concepts. Recombination refers to the exchange of genetic material between homologous chromosomes during meiosis, which can result in new combinations of alleles. The 'phase' of alleles refers to the arrangement of alleles on the parental chromosomes.
Step 3: Analyze the pedigree. Examine the genotypes of generation II individuals to determine the phase of alleles (which allele is linked to NF1 on the same chromosome). This involves identifying which allele (1 or 2) is consistently inherited with NF1 in generation II.
Step 4: Compare the genotypes of generation III offspring. Check if any offspring have inherited a combination of alleles that differs from the parental phase established in generation II. If such combinations exist, it indicates recombination.
Step 5: Summarize findings. Based on the comparison, determine whether evidence of recombination is present among the eight offspring in generation III. Provide reasoning based on the observed inheritance patterns and linkage of alleles.

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Key Concepts

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

Autosomal Dominant Inheritance

Autosomal dominant inheritance refers to a pattern where only one copy of a mutated gene from an affected parent can cause the disorder in offspring. This means that if a parent has the disorder, there is a 50% chance for each child to inherit the condition. Neurofibromatosis 1 (NF1) exemplifies this inheritance pattern, as it is caused by mutations in a gene located on an autosome, specifically chromosome 17.
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Genetic Linkage and Markers

Genetic linkage occurs when genes are located close to each other on a chromosome and tend to be inherited together. DNA markers, which are specific sequences of DNA with known locations, can be used to track the inheritance of traits. In the context of NF1, the presence of a DNA marker with two alleles linked to the NF1 gene helps researchers determine the inheritance patterns and potential recombination events during meiosis.
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Recombination

Recombination is the process during meiosis where homologous chromosomes exchange genetic material, leading to new allele combinations in offspring. This can affect the inheritance of linked genes, such as the NF1 gene and its associated DNA markers. By analyzing the genotypes of offspring in generation III, one can determine if recombination has occurred by observing whether the offspring exhibit combinations of alleles that differ from those of their parents.
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Related Practice
Textbook Question

In tomatoes, the allele T for tall plant height is dominant to dwarf allele t, the P allele for smooth skin is dominant to the p allele for peach fuzz skin, and the allele R for round fruit is dominant to the recessive r allele for oblong fruit. The genes controlling these traits are linked on chromosome 1 in the tomato genome, and the genes are arranged in the order and with the recombination frequencies shown.

What are the genotypes of gametes produced by the F₁, and what is the predicted frequency of each gamete?

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Textbook Question

In tomatoes, the allele T for tall plant height is dominant to dwarf allele t, the P allele for smooth skin is dominant to the p allele for peach fuzz skin, and the allele R for round fruit is dominant to the recessive r allele for oblong fruit. The genes controlling these traits are linked on chromosome 1 in the tomato genome, and the genes are arranged in the order and with the recombination frequencies shown.

The F₁ are test-crossed to dwarf, peach fuzz, oblong plants, and 1000 test-cross progeny are produced. What are the phenotypes of test-cross progeny, and what number of progeny is expected in each class?

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Textbook Question

Neurofibromatosis 1 (NF1) is an autosomal dominant disorder inherited on human chromosome 17. Part of the analysis mapping the NF1 gene to chromosome 17 came from genetic linkage studies testing segregation of NF1 and DNA genetic markers on various chromosomes. A DNA marker with two alleles, designated 1 and 2, is linked to NF1. The pedigree below shows segregation of NF1 (darkened symbols) and gives genotypes for the DNA marker for each family member.

Determine the alleles for the NF1 gene and the DNA marker gene on each chromosome carried by the four family members in generation I and generation II. Use N for the dominant NF1 allele and n for the recessive allele and assume I-1 is heterozygous for the disease allele (Nn).

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Textbook Question

Neurofibromatosis 1 (NF1) is an autosomal dominant disorder inherited on human chromosome 17. Part of the analysis mapping the NF1 gene to chromosome 17 came from genetic linkage studies testing segregation of NF1 and DNA genetic markers on various chromosomes. A DNA marker with two alleles, designated 1 and 2, is linked to NF1. The pedigree below shows segregation of NF1 (darkened symbols) and gives genotypes for the DNA marker for each family member.

What is the estimated recombination frequency between the NF1 gene and the DNA marker?

831
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Textbook Question

A 2006 genetic study of a large American family (Ikeda et al., 2006) identified genetic linkage between DNA markers on chromosome 11 and the gene producing the autosomal dominant neuromuscular disorder spinocerebellar ataxia type 5 (SCA5). The following lod score data are taken from the 2006 study:                  

Does either group of lod scores indicate statistically significant odds in favor of genetic linkage? Explain your answer.

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Textbook Question

A 2006 genetic study of a large American family (Ikeda et al., 2006) identified genetic linkage between DNA markers on chromosome 11 and the gene producing the autosomal dominant neuromuscular disorder spinocerebellar ataxia type 5 (SCA5). The following lod score data are taken from the 2006 study:                  

What is the maximum value for each set of lod scores?

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