Deck 23: Quantitative Genetics

Question 1

The principles that determine the inheritance of quantitative characteristics are the same as the principles that determine the inheritance of discontinuous characteristics, but more genes take part in the determination of quantitative characteristics.
-Briefly explain how the number of genes influencing a polygenic trait can be determined?

Answer 1

Cross two individuals that are each homozygous for different genes affecting the traits and then intercross the resulting $F_1$ progeny to produce the $F_2$ . Determine what proportion of the $F_2$ progeny resembles one of the original homozygotes in the P generation. This proportion should be $(1/4)^n$ , where n equals the number of loci with a segregating pair of alleles that affect the characteristic.

Question 2

In statistics, the population is the group of interest; a sample is a subset of the population. The sample should be representative of the population and large enough to minimize chance differences between the population and the sample.

-A geneticist is interested in whether asthma is caused by a mutation in the DS112 gene. The geneticist collects DNA from 120 people with asthma and 100 healthy people and sequences the DNA. She finds that 35 of the people with asthma and none of the healthy people have a mutation in the DS112 gene. What is the population in this study?

A) The 120 people with asthma
B) The 100 healthy people
C) The 35 people with a mutation in their gene
D) All people with asthma

Answer 2

All people with asthma

Question 3

The mean and variance describe a distribution of measurements: the mean provides information about the location of the center of a distribution, and the variance provides information about its variability.

-The measurements of a distribution with a higher ______ will be more spread out.

A) mean
B) variance
C) standard deviation
D) variance and standard deviation

Answer 3

variance and standard deviation

Question 4

A correlation coefficient measures the strength of association between two variables. The sign (positive or negative) indicates the direction of the correlation; the absolute value measures the strength of the association. Regression is used to predict the value of one variable on the basis of the value of a correlated variable.

-In Lubbock, Texas, rainfall and temperature exhibit a significant correlation of -0.7. Which conclusion is correct?

A) There is usually more rainfall when the temperature is high.
B) There is usually more rainfall when the temperature is low.
C) Rainfall is equally likely when the temperature is high or low.

Question 5

Broad-sense heritability is the proportion of phenotypic variance that is due to genetic variance. Narrow-sense heritability is the proportion of phenotypic variance that is due to additive genetic variance. Heritability can be measured by eliminating one of the variance components, by analyzing parent-offspring regression, or by comparing individuals having different degrees of relatedness.

-If the environmental variance $(V_E)$ increases and all other variance components remain the same, what will the effect be?

A) Broad-sense heritability will decrease.
B) Broad-sense heritability will increase.
C) Narrow-sense heritability will increase.
D) Broad-sense heritability will increase, but narrow-sense heritability will decrease

Question 6

Heritability provides information only about the degree to which variation in a characteristic is genetically determined. There is no universal heritability for a characteristic; heritability is specific for a given population in a specific environment. Environmental factors can potentially affect characteristics with high heritability, and heritability says nothing about the nature of population differences in a characteristic.
-Suppose that you just learned that the narrow-sense heritability of blood pressure measured among a group of African Americans in Detroit, Michigan, is 0.40. What does this heritability tell us about genetic and environmental contributions to blood pressure?

Question 7

The response to selection is influenced by narrow-sense heritability and the selection differential.
-The narrow-sense heritability for a trait is 0.4 and the selection differential is 0.5. What is the predicted response to selection?

Question 8

Genetic correlations result from pleiotropy. When two characteristics are genetically correlated, selection for one characteristic will produce a correlated response in the other characteristic.

-In a herd of dairy cattle, milk yield and the percentage of butterfat exhibit a genetic correlation of -0.38. If greater milk yield is selected in this herd, what will be the effect on the percentage of butterfat?