43. A Lod score of 3 represents a Recombination Frequency that is
(1) 3 times as likely as the hypothesis of no linkage
(2) 30 times as likely as the hypothesis of no linkage
(3) 100 times as likely as the hypothesis of no linkage
(4) 1000 times as likely as the hypothesis of no linkage
Introduction to Lod Score and Recombination Frequency
In genetic linkage analysis, the Lod score (Logarithm of the Odds) is a statistical measure used to evaluate whether two loci (genes or markers) are likely linked or independently assorted. It compares the likelihood of observing a particular recombination frequency under the hypothesis of linkage versus no linkage. Specifically, a Lod score of 3 has a critical significance threshold in genetics.
Detailed Explanation of Lod Score of 3
A Lod score of 3 means the data supporting linkage is 1000 times more likely than the data supporting no linkage (independent assortment). This is because the Lod score is the base 10 logarithm of the odds ratio. Mathematically, Lod score = log10(odds ratio), so a Lod score of 3 means:
Odds ratio=103=1000
Thus, with a Lod score of 3, the observed recombination frequency is 1000 times as likely if the loci are linked than if they are unlinked.
Explanation of Each Multiple Choice Option
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3 times as likely: This is incorrect because a Lod score of 3 is a log scale; it corresponds to the power of 10, not a multiple of 3.
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30 times as likely: This is incorrect; it underestimates the odds implied by a Lod score of 3.
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100 times as likely: Also incorrect; represents a Lod score of 2 (since 102=100), not 3.
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1000 times as likely: Correct option because a Lod score of 3 means the probability of linkage is 1000 times greater than no linkage, indicating significant evidence for linkage.
SEO-Focused Summary
A Lod score of 3 in genetics indicates strong evidence for linkage, meaning the observed recombination frequency is 1000 times more likely if the genes are physically linked than if they assort independently. This threshold is widely used in genetic studies to confirm linkage. Misinterpretations like thinking it means 3, 30, or 100 times the odds are common but incorrect because the Lod score uses a logarithmic base-10 scale.
This explanation clarifies the interpretation of a Lod score of 3 with reference to recombination frequency and the likelihood ratio in linkage studies, helping students and researchers accurately understand this important genetic concept.
