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

Key Concepts

Lod Score

A lod score (logarithm of the odds) is a statistical measure used in genetics to evaluate the likelihood of a particular genetic linkage. It compares the probability of observing the data if two loci are linked versus if they are unlinked. A lod score of 3 or higher is typically considered significant evidence for linkage, indicating that the loci are likely inherited together.

Theta (θ) Value

Theta (θ) represents the recombination fraction between two genetic markers, indicating the probability that a crossover will occur between them during meiosis. Values range from 0 (no recombination, markers are linked) to 0.5 (independent assortment). Understanding θ is crucial for interpreting lod scores, as it directly influences the likelihood of linkage between genes.

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, and each child of an affected parent has a 50% chance of inheriting the condition. Spinocerebellar ataxia type 5 (SCA5) is an example of a disorder that follows this inheritance pattern.