Question 1

_____ of a trait in a population is the proportion of the total variation in the trait (phenotypic variation) that is due to genetic differences among individuals.

Accepted Answer

Heritability is a measure that describes the proportion of phenotypic variation in a population that is due to genetic variation among individuals. This measure ranges from 0 to 1, with high heritability indicating that a trait is largely influenced by genetics, and low heritability suggesting that other factors, such as the environment, play a greater role in determining the trait.

Question 2

If genetically different strains of corn are grown in a greenhouse and subject to identical environmental conditions, then differences in height would be due to genetic differences and the heritability measure would:

Accepted Answer

If genetically different strains of corn are grown under identical environmental conditions, any differences in height can be attributed solely to genetics. Therefore, the heritability measure would be 100%, indicating that variation in height is entirely due to genetic factors.

Question 3

If genetically identical strains of corn are grown in different environments, then differences in height would be due to the environment and the heritability measure would:

Accepted Answer

If genetically identical strains of corn are grown in different environments and differences in height are observed, it indicates that the trait is highly influenced by environmental factors and not by genetic factors. Therefore, the heritability measure would be close to 0% as there is no genetic variation that is contributing to the observed differences.

Question 4

The overall results represented in Figure 18.7 suggest that offspring exhibit an average phenotype that is more different from the population mean than that of their parents.

Accepted Answer

The answer of The overall results represented in Figure 18.7...

Question 5

Imagine that one of your good friends comes from a tall family. You measure the height of your friend and her two brothers. What would you expect of the average height of your friend and her siblings?

Accepted Answer

Due to regression towards the mean, the children's average height is likely to be closer to the population mean than their parents', but still above the population mean due to the tall family background.

Question 6

The magnitude of heritability is an intrinsic property of a trait.

Accepted Answer

Heritability is not an intrinsic property of a trait but rather a measure of how much of the variation in a trait across a population is due to genetic differences among individuals within a specific environment. It can vary depending on the population and environmental conditions studied.

Question 7

Heritability applies only to the traits in a particular population across the range of environments that exist for that population at a given time.

Accepted Answer

Heritability is a measure of the proportion of observed variation in a trait that can be attributed to genetics in a particular population at a given time and set of environmental conditions. Therefore, it only applies to that specific population and its environment, not to other populations or different environments.

Question 8

Heritability in nonscientific terms means "the capability of being inherited or being passed on by inheritance"; this is an accurate description of the inheritance of a complex trait.

Accepted Answer

Heritability in scientific terms refers to the proportion of variation in a trait that can be attributed to genetic differences among individuals in a population, not the capability of being inherited.

Question 9

Francis Galton, a contemporary of Charles Darwin, studied variation in complex traits such as human height. Use the bar graphs shown below to answer the following question: Which of the following statements best describes Figure 18.7 graph (b), which depicts Galton's data showing distribution of offspring height from the shortest parents he studied?

Accepted Answer

Figure 18.7 graph (b) shows a positively skewed distribution, meaning that there are more offspring with heights above the mean than below it. This suggests that the offspring from the shortest parents are taller on average than their parents, and therefore the parental mean for the shortest parents is smaller than the mean height of their offspring.

Question 10

If all of the variation in a trait in the population is due to differing genotypes, then the mean phenotype of the offspring would be identical to the parental mean.

Accepted Answer

If all of the variation in a trait is due to differing genotypes, it means that the environment does not play a role in influencing the trait. In this case, the mean phenotype of the offspring would be identical to the parental mean because there are no environmental factors affecting the trait.

Question 11

If all of the variation in a trait in the population is due to differences in the environment, then the mean phenotype of the offspring would be independent of parental phenotype and would be identical to the mean phenotype of the population.

Accepted Answer

If all variation in a trait is due to differences in the environment, then parental phenotype would not have any influence on the mean phenotype of the offspring. As a result, the mean phenotype of the offspring would be identical to the mean phenotype of the population.

Question 12

A scientist measured heritability in yield per acre of a strain of wheat grown on a farm in eastern Europe and determined that it was 80%. She can therefore conclude that:

Accepted Answer

Heritability estimates are specific to the population and environment in which they were measured. They do not necessarily apply to different environments, times, or explain the proportion of yield due to genetics versus environment in a direct way.

Question 13

When heritability is 0%, genes play:

Accepted Answer

The answer of When heritability is 0%, genes play:
...

Question 14

Consider a trait determined entirely by environmental risk factors for which the chance that a random individual is affected is 20%. What is the concordance between identical twins? What is the concordance between same-sex fraternal twins?

Accepted Answer

The answer of Consider a trait determined entirely by environmental...

Question 15

Which of the following statements is TRUE regarding heritability?

Accepted Answer

Heritability is a measure of how much of the variation in a trait within a population is due to genetic differences among individuals, rather than the statements provided which contain inaccuracies or misunderstandings about the concept.

Question 16

An example of "regression toward the mean" would be if the offspring of two short parents had an average height equal to the average height of the parents-not of the population as a whole.

Accepted Answer

Regression toward the mean suggests that the offspring of two short parents would likely be taller than their parents, moving closer to the average height of the population, not remaining at the height of the parents.

Question 17

The data in the graph below show the concordance between identical twins and same-sex fraternal twins for five complex traits. Based on these data, which of the traits shows the GREATEST effect of heredity relative to environment?

Accepted Answer

Trait K shows the greatest difference in concordance between identical twins and same-sex fraternal twins, indicating the strongest influence of heredity relative to environment. The concordance rate for identical twins is approximately 0.8, while the concordance rate for same-sex fraternal twins is around 0.4. This suggests that trait K is heavily influenced by genetic factors, with only a moderate contribution from environmental factors.

Question 18

Consider a trait determined entirely by three independently assorting genes with two alleles in which one allele is dominant over the other. As in the wheat seed color example illustrated in Figure 18.4, imagine that each dominant allele contributes one unit to the phenotype of the trait. Individuals with a phenotype of $\ge$ 4 are affected and all other phenotypes are not affected. What is the concordance between same-sex fraternal twins?

Accepted Answer

The concordance rate for same-sex fraternal twins is calculated based on the probability that both twins inherit the same combination of alleles that result in the affected phenotype. Since fraternal twins share about 50% of their genes, the probability of both being affected is lower than that of identical twins. Given the genetic model described, the concordance rate is approximately 21%.

Question 19

A trait with high heritability responds rapidly to selection, whereas a trait with a low heritability responds slowly or not at all.

Accepted Answer

This is because heritability is the proportion of variation in a trait that is due to genetic factors. If a trait has a high heritability, then genetic factors play a stronger role in determining that trait, and therefore selecting individuals with desirable traits will cause a more rapid change in the trait's frequency within a population over time. On the other hand, if a trait has a low heritability, then genetic factors play a smaller role, and selecting individuals with desirable traits will have less of an impact on the trait's frequency within a population.

Question 20

Francis Galton, a contemporary of Charles Darwin, studied variation in complex traits such as human height. Use the bar graphs shown below to answer the following question: Which of the following statements BEST describes graph (a), which depicts Galton's data showing distribution of offspring height from the tallest parents he studied?

Accepted Answer

The answer of Francis Galton, a contemporary of Charles Darwin,...

Quiz 18: The Genetic and Environmental Basis of Complex Traits