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Chapter 7: Problem 36

A group of geneticists are interested in identifying genes that may play a role in susceptibility to asthma. They study the inheritance of genetic markers in a series of families that have two or more asthmatic children. They find an association between the presence or absence of asthma and a genetic marker on the short arm of chromosome 20 and calculate a lod score of 2 for this association. What does this lod score indicate about genes that may influence asthma?

Short Answer

Expert verified
A LOD score of 2 indicates some evidence of linkage between the genetic marker and asthma, but it is not conclusive. More evidence is needed to confirm the linkage.

Step by step solution

01

Understanding the LOD Score

The LOD score, or logarithm of the odds, is a statistical measure used to estimate the likelihood that two loci are linked. A LOD score is calculated based on the ratio of the probability of observing the data if the loci are linked, to the probability of observing the data if the loci are not linked.
02

Interpreting Positive LOD Score

A positive LOD score indicates evidence in favor of linkage. In genetic studies, a LOD score of 3 or higher is considered significant evidence of linkage, meaning there is a 1000 to 1 chance that the loci are linked. Conversely, a LOD score less than -2 suggests no linkage.
03

Interpreting LOD Score of 2

A LOD score of 2 indicates some evidence of linkage, though it is not considered conclusive. Specifically, this score suggests a 100 to 1 likelihood that the genetic marker on the short arm of chromosome 20 and the asthma susceptibility gene are linked. However, further corroborating evidence would be needed to strongly support this association.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Genetic Linkage
Genetic linkage refers to the tendency of genes or genetic markers that are located close to each other on a chromosome to be inherited together during meiosis, the process that generates gametes.
Linkage occurs because the closer two genes are on a chromosome, the less likely they are to be separated by a crossover event during meiosis. This results in them being passed to the next generation together.
  • Genes that are close together are said to be 'linked', and this concept is crucial for understanding heredity.
  • Genetic linkage allows researchers to map the location of genes on chromosomes.
  • The calculation of LOD (Logarithm of the Odds) scores is commonly used to assess genetic linkage. A higher LOD score suggests stronger evidence for linkage.
By studying genetic linkage, scientists can pinpoint where genes influencing specific traits, such as diseases, might be located on a chromosome.
Asthma Genetics
Asthma is a complex respiratory condition, with both genetic and environmental factors contributing to its development.
Genetically, multiple genes have been associated with asthma, indicating a polygenic inheritance pattern.
  • Genetic studies have identified various loci where changes influence susceptibility to asthma, often involving genes that affect the immune system or inflammation.
  • The search for asthma-related genes involves tracking genetic markers across families with asthma history to find linked regions.
  • Understanding the genetic bases of asthma could lead to better-targeted therapies and interventions.
The study of asthma genetics is vital as it unravels the hereditary aspects of the disease, potentially identifying specific genes that increase susceptibility.
Chromosome 20
Chromosome 20 is one of the 23 pairs of human chromosomes and carries thousands of genes necessary for human development and function.
Within genetic research, chromosome 20 has been identified as being linked to various conditions, including, as this exercise indicates, asthma.
  • The short arm of chromosome 20, known as 20p, is of particular interest in studies surrounding genetic diseases and traits.
  • Genetic markers located on 20p can provide insights into hereditary conditions, like asthma, by highlighting regions potentially linked to disease susceptibility.
  • Researchers focus on specific areas, such as the short arm of chromosome 20, to gather more precise data on the genes affecting certain diseases.
By investigating chromosome 20, scientists aim to discover and understand genes that may predispose individuals to asthma and other conditions.
Genetic Markers
Genetic markers are specific sequences in the genome that can be consistently identified and tracked across different individuals.
They are used in genetic research to help locate genes associated with specific diseases.
  • Markers can be short DNA sequences, single nucleotide polymorphisms (SNPs), or microsatellites.
  • They serve as signposts on the genome, indicating likely regions for gene-disease associations.
  • When a genetic marker shows linkage with a disease, it points researchers toward the location of the potential disease-causing gene.
In the context of asthma, identifying genetic markers that show linkage to the condition can lead to insights into its genetic causes, paving the way for more effective treatments and preventive measures.

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Most popular questions from this chapter

In a testcross for two genes, what types of gametes are produced with (a) complete linkage, (b) independent assortment, and (c) incomplete linkage?

Explain how to determine, using the numbers of progeny from a three point cross, which of three linked loci is the middle locus.

Why do calculated recombination frequencies between pairs of loci that are located far apart underestimate the true genetic distances between loci?

What does the term recombination mean? What are two causes of recombination?

In the snail Cepaea nemoralis, an autosomal allele causing a banded shell \(\left(B^{B}\right)\) is recessive to the allele for an unbanded shell \(\left(B^{O}\right)\). Genes at a different locus determine the background color of the shell; here, yellow \(\left(C^{Y}\right)\) is recessive to brown \(\left(C^{B w}\right) .\) A banded, yellow snail is crossed with a homozygous brown, unbanded snail. The \(\mathrm{F}_{1}\) are then crossed with banded, yellow snails (a testcross). a. What will the results of the testcross be if the loci that control banding and color are linked with no crossing over? b. What will the results of the testcross be if the loci assort independently? c. What will the results of the testcross be if the loci are linked and 20 m.u. apart?
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