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Ch. 20 - Population Genetics and Evolution at the Population, Species, and Molecular Levels
Sanders - Genetic Analysis: An Integrated Approach 3rd Edition
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Capitolo 20, Problema 9

George Udny Yule was wrong in suggesting that an autosomal dominant trait like brachydactyly will increase in frequency in populations. Explain why Yule was incorrect.

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Understand the concept of autosomal dominant traits: These are traits where only one copy of the dominant allele is needed for the trait to be expressed.
Consider the Hardy-Weinberg principle: This principle states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of other evolutionary influences.
Identify the factors that can change allele frequencies: These include mutation, selection, gene flow, genetic drift, and non-random mating.
Recognize that Yule's assumption ignores these factors: Yule assumed that the frequency of a dominant trait would naturally increase, but this ignores the balance of evolutionary forces that can maintain or even decrease allele frequencies.
Conclude that dominance does not equate to increased frequency: The dominance of an allele does not inherently lead to an increase in its frequency without selective advantage or other evolutionary pressures.

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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 trait to manifest in offspring. This means that individuals with the trait have a 50% chance of passing it on to their children. However, the trait's frequency in a population can be influenced by factors such as fitness and reproductive success.
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04:37
Variations on Dominance

Population Genetics

Population genetics studies the distribution and change in frequency of alleles within populations. Factors such as natural selection, genetic drift, and mutation can affect allele frequencies. In the case of brachydactyly, if the trait negatively impacts reproductive success, its frequency may not increase despite being autosomal dominant.
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03:45
Descriptive Genetics

Fitness and Natural Selection

Fitness in genetics refers to an organism's ability to survive and reproduce in its environment. Natural selection can lead to a decrease in the frequency of traits that are disadvantageous for survival or reproduction. If brachydactyly reduces an individual's fitness, Yule's assumption that it would increase in frequency is flawed, as natural selection would likely counteract this increase.
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Natural Selection
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