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:                                     Theta (θ) Value               0.01    0.05     0.10     0.20     0.30     0.40SCA5    11.02   12.26   11.94   10.04    7.26     3.77 and DNA marker A SCA5    0.35.    0.94.     1.07     0.99     0.75    0.43 and DNA marker B Does either group of lod scores indicate statistically significant odds in favor of genetic linkage? Explain your answer.

Verified step by step guidance

1. Understand that a LOD (logarithm of the odds) score is used to determine the likelihood of genetic linkage between a marker and a trait. A LOD score of 3 or higher is generally considered evidence of linkage.
2. Examine the LOD scores for DNA marker A: 11.02, 12.26, 11.94, 10.04, 7.26, and 3.77. All these scores are above 3, indicating strong evidence of linkage.
3. Examine the LOD scores for DNA marker B: 0.35, 0.94, 1.07, 0.99, 0.75, and 0.43. All these scores are below 3, indicating no significant evidence of linkage.
4. Compare the LOD scores for both markers. Marker A consistently shows scores above 3, while Marker B does not reach the threshold of 3 in any instance.
5. Conclude that the LOD scores for DNA marker A indicate statistically significant odds in favor of genetic linkage, whereas the scores for DNA marker B do not.

Key Concepts

Lod Score

A lod score (logarithm of the odds) is a statistical measure used to evaluate the likelihood of genetic linkage between a trait and a specific genetic marker. A lod score greater than 3 is typically considered evidence of significant linkage, while a score less than -2 suggests no linkage. In the context of the study, analyzing the lod scores for different theta values helps determine if the observed genetic markers are associated with the SCA5 disorder.

Theta (θ) Value

Theta (θ) represents the recombination fraction, which is the probability that a crossover will occur between two loci during meiosis. It ranges from 0 to 0.5, where 0 indicates complete linkage (no recombination) and 0.5 indicates independent assortment. In the context of the lod score analysis, different theta values are used to assess the strength of the genetic linkage between the markers and the SCA5 gene.

Autosomal Dominant Inheritance

Autosomal dominant inheritance is a pattern where only one copy of a mutated gene from an affected parent can cause the disorder in offspring. This means that the trait can be passed down through generations, with each child having a 50% chance of inheriting the condition. Understanding this inheritance pattern is crucial for interpreting the genetic linkage findings in the study, as it informs the expected distribution of the disorder within the family.