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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 28c
Chapter 5, Problem 28c

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 darkened symbols for affected individuals and genotypes for a DNA marker.
What is the estimated recombination frequency between the NF1 gene and the DNA marker?

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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 estimate the recombination frequency between the NF1 gene and the DNA marker using the pedigree chart provided.
Step 2: Analyze the pedigree chart. Identify individuals with NF1 (darkened symbols) and their genotypes for the DNA marker. Note that the father (1,2 genotype) has NF1, while the mother (2,2 genotype) does not. The offspring's genotypes and NF1 status are also provided.
Step 3: Determine parental alleles. The father contributes either allele 1 or allele 2 to his offspring, while the mother contributes allele 2. Recombination occurs when the NF1 gene and the DNA marker are inherited separately, breaking the linkage.
Step 4: Count recombinants and non-recombinants. Compare the offspring's genotypes and NF1 status to identify recombinants (NF1 inherited with allele 2) and non-recombinants (NF1 inherited with allele 1). Count the number of each type.
Step 5: Calculate recombination frequency. Use the formula: recombination frequency = (number of recombinants / total offspring) × 100%. This provides the percentage of recombination events between the NF1 gene and the DNA marker.

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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. In the case of Neurofibromatosis 1 (NF1), this means that an individual with the NF1 gene mutation has a 50% chance of passing it on to each child, regardless of the child's sex. This pattern is crucial for understanding the pedigree analysis and the inheritance of NF1.
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Recombination Frequency

Recombination frequency is a measure of the likelihood that two genes will be separated during meiosis due to crossing over. It is calculated as the number of recombinant offspring divided by the total number of offspring. In genetic linkage studies, a lower recombination frequency indicates that two genes are closely linked on the same chromosome, which is essential for estimating the distance between the NF1 gene and the DNA marker in the provided pedigree.
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Genetic Linkage Studies

Genetic linkage studies investigate the co-segregation of genes and genetic markers within families to determine their relative positions on chromosomes. By analyzing the inheritance patterns of traits and associated markers, researchers can identify linked genes, such as the NF1 gene on chromosome 17. These studies are fundamental for mapping genetic disorders and understanding their inheritance patterns, as seen in the analysis of NF1.
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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.

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.

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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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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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:                  

Based on the available information, is DNA marker A linked to the gene producing SCA5? Explain your answer.

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