Block 7 Repro Genetics MCQ's Prt 2

1. Imagine a species of Giraffes living on the savanna in Africa. The overall size of these varies as expected for a quantitative trait. The smallest giraffes have difficulty surviving, because they cannot reach the leafs on the trees that this species feed on. The largest giraffes have difficulty growing muscle large enough to move the massive bones needed for supporting this size of an animal. Therefore, the giraffes closest to the average size stand the best chance of surviving and reproducing. This is an example of which special concept?

Stabilizing selection

Disruptive selection

Directional selection

Founder effect

Genetic drift

The given scenario describes stabilizing selection. Stabilizing selection occurs when individuals with average or intermediate traits have a higher fitness compared to individuals with extreme traits. In this case, the giraffes closest to the average size are more likely to survive and reproduce because they can effectively reach the leaves on trees for food and their muscle size is suitable for supporting their body size. This leads to a narrowing of the trait distribution over time, as extreme traits are selected against.

Explanation

The given scenario describes stabilizing selection. Stabilizing selection occurs when individuals with average or intermediate traits have a higher fitness compared to individuals with extreme traits. In this case, the giraffes closest to the average size are more likely to survive and reproduce because they can effectively reach the leaves on trees for food and their muscle size is suitable for supporting their body size. This leads to a narrowing of the trait distribution over time, as extreme traits are selected against.

2. If you have high cholesterol, you may consider taking statins to help lower the levels. If you have desirable alleles in both the cholesteryl ester transfer protein and multidrug resistance transporter genes, the statin Fluvostatin will work well. However, if you have only undesirable alleles in both genes you will want to avoid Fluvostatin. If you have a mixture of desirable and undesirable alleles, then the number of each will determine the outcome. This description best fit which of the following concepts?

Assortative mating

Allele sharing

Additive effects

Low heritability

Anticipation

The given description best fits the concept of "additive effects". It explains that the outcome of taking the statin Fluvostatin depends on the combination of desirable and undesirable alleles in the cholesteryl ester transfer protein and multidrug resistance transporter genes. The description suggests that the effect of these alleles is additive, meaning that the presence of desirable alleles will have a positive effect on the outcome, while the presence of undesirable alleles will have a negative effect. Therefore, the overall outcome is determined by the number of each type of allele present.

Explanation

The given description best fits the concept of "additive effects". It explains that the outcome of taking the statin Fluvostatin depends on the combination of desirable and undesirable alleles in the cholesteryl ester transfer protein and multidrug resistance transporter genes. The description suggests that the effect of these alleles is additive, meaning that the presence of desirable alleles will have a positive effect on the outcome, while the presence of undesirable alleles will have a negative effect. Therefore, the overall outcome is determined by the number of each type of allele present.

3. In a condition such as schizophrenia the recurrence risk will be greatest for which of the following relatives of an affected individual?

Brother

Nephew

Grandchild

Aunt

The recurrence risk for schizophrenia is greatest for siblings, such as a brother, of an affected individual. This is because siblings share a higher percentage of their genetic material compared to other relatives. Therefore, the chances of inheriting the genetic factors that contribute to schizophrenia are higher among siblings.

Explanation

The recurrence risk for schizophrenia is greatest for siblings, such as a brother, of an affected individual. This is because siblings share a higher percentage of their genetic material compared to other relatives. Therefore, the chances of inheriting the genetic factors that contribute to schizophrenia are higher among siblings.

4. To determine if there is a relationship between two variables such that as one variable changes the other also changes, we would calculate a

Variance

Standard error

Correlation coefficient

Coefficient of variation

The correlation coefficient measures the strength and direction of the linear relationship between two variables. It ranges from -1 to 1, where -1 indicates a perfect negative correlation, 1 indicates a perfect positive correlation, and 0 indicates no correlation. By calculating the correlation coefficient, we can determine if there is a relationship between the two variables and the extent to which they vary together.

Explanation

The correlation coefficient measures the strength and direction of the linear relationship between two variables. It ranges from -1 to 1, where -1 indicates a perfect negative correlation, 1 indicates a perfect positive correlation, and 0 indicates no correlation. By calculating the correlation coefficient, we can determine if there is a relationship between the two variables and the extent to which they vary together.

5. In last century, several countries instituted policies where sterilization was forced on, for example, people with mental retardation. In addition to this being ethically questionable, it was also wrong because:

Most of the cases caused by dominant diseases come from new mutations

Most of the cases caused by autosomal recessive genes are due to new mutations

Most dominant alleles are hidden in heterozygotes

The recessive alleles lost are insignificant compared to those hidden in heterozygotes

The phenotypes is a side effect of elements that are beneficial to mankind

Forced sterilization policies on individuals with mental retardation in the last century were ethically questionable and wrong because most of the cases caused by dominant diseases come from new mutations. This means that sterilizing individuals with mental retardation would not have prevented the spread of these diseases, as the majority of cases are not inherited but rather result from spontaneous mutations. Therefore, the forced sterilization policies were ineffective in addressing the issue they were intended to solve.

Explanation

Forced sterilization policies on individuals with mental retardation in the last century were ethically questionable and wrong because most of the cases caused by dominant diseases come from new mutations. This means that sterilizing individuals with mental retardation would not have prevented the spread of these diseases, as the majority of cases are not inherited but rather result from spontaneous mutations. Therefore, the forced sterilization policies were ineffective in addressing the issue they were intended to solve.

6. Which of the following observations is the strongest evidence for an important genetic component in the causation of type-1 diabetes mellitus (IDDM)?

Pancreatic b-cell autoantibodies are frequently present

Approximately 10% of affected indivifuals have an affected sibling

Onset of disease is usually in childhood.

The concordance rate in monozygotic twins is approximately 30%.

The concordance rate in monozygotic twins is five times that in dizygotic twins.

Remember that monozygotic (MZ) twins have identical genotypes and dizygotic (DZ) twins share only 50% of their genetic information. Therefore if a trait is non-genetically determined then there should be no difference in the concordance rate (how often members of a twin pair show the same phenotype) between MZ and DZ twin pairs. If a trait has a genetic component then the rate of concordance is expected to be higher in MZ twins then in DZ twins.

Explanation

Remember that monozygotic (MZ) twins have identical genotypes and dizygotic (DZ) twins share only 50% of their genetic information. Therefore if a trait is non-genetically determined then there should be no difference in the concordance rate (how often members of a twin pair show the same phenotype) between MZ and DZ twin pairs. If a trait has a genetic component then the rate of concordance is expected to be higher in MZ twins then in DZ twins.

7. The average recurrence risk for a couple that has had a child with cleft lip, a multifactorial birth defect, is approximately 4%. What is the recurrence risk if the couple has two affected children?

2%

4%

10%

25%

50%

When looking at the inheritance of multifactorial traits, as the number of affected children within a single family increases, the recurrence risk also increases.

Explanation

When looking at the inheritance of multifactorial traits, as the number of affected children within a single family increases, the recurrence risk also increases.

8. Which of the following conditions does not show multifactorial inheritance?

Pyloric stenosis

Schizophrenia

Spina bifida (neural tube defects)

Marfan syndrome

Marfan syndrome is not an example of multifactorial inheritance because it is caused by a mutation in a single gene, specifically the FBN1 gene. Multifactorial inheritance involves the interaction of multiple genes as well as environmental factors. Pyloric stenosis, schizophrenia, and spina bifida are all examples of conditions that can be influenced by multiple genes and environmental factors, making them examples of multifactorial inheritance.

Explanation

Marfan syndrome is not an example of multifactorial inheritance because it is caused by a mutation in a single gene, specifically the FBN1 gene. Multifactorial inheritance involves the interaction of multiple genes as well as environmental factors. Pyloric stenosis, schizophrenia, and spina bifida are all examples of conditions that can be influenced by multiple genes and environmental factors, making them examples of multifactorial inheritance.

9. Given 1 locus with 2 alleles that are strictly additive, the additive genetic variance (2pqa^2) is at a maximum when

Q = 0.5

Q = 1.0

Q = 0.0

P = 0.25

The additive genetic variance is at a maximum when q = 0.5. This is because the additive genetic variance is calculated using the formula 2pqa^2, where p and q represent the frequencies of the two alleles and a represents the effect of the allele on the phenotype. When q = 0.5, it means that both alleles are present in equal frequencies in the population. This allows for maximum variation in the genetic makeup of the individuals in the population, leading to a higher additive genetic variance.

Explanation

The additive genetic variance is at a maximum when q = 0.5. This is because the additive genetic variance is calculated using the formula 2pqa^2, where p and q represent the frequencies of the two alleles and a represents the effect of the allele on the phenotype. When q = 0.5, it means that both alleles are present in equal frequencies in the population. This allows for maximum variation in the genetic makeup of the individuals in the population, leading to a higher additive genetic variance.

10. At the D locus, there are two alleles with "D" incompletely dominant to "d". Population A has a frequency of the "D" allele equal to 0.6 (p = 0.6), while population B has a frequency of the "D" allele equal to 0.8 (p = 0.8). Which of the following statements is true?

Va is greater in population B

Va is greater in population A

Va is equal in both populations

No conclusion can be drawn about the variance of either population.

The frequency of the "D" allele in population A is lower than in population B. Since "D" is incompletely dominant to "d", it means that individuals with the "Dd" genotype will have a phenotype that is intermediate between the "DD" and "dd" genotypes. This suggests that there is more genetic variation in population A, as there is a higher proportion of individuals with the "Dd" genotype. Therefore, the variance in population A is likely to be greater than in population B.

Explanation

The frequency of the "D" allele in population A is lower than in population B. Since "D" is incompletely dominant to "d", it means that individuals with the "Dd" genotype will have a phenotype that is intermediate between the "DD" and "dd" genotypes. This suggests that there is more genetic variation in population A, as there is a higher proportion of individuals with the "Dd" genotype. Therefore, the variance in population A is likely to be greater than in population B.

11. Which of the following statements about Hirschsprung disease is incorrect?

It shows an association with Down syndrome.

It is more common in girls than in boys.

RET is a major susceptibility gene

Recurrence risks are greater for long segment disease than for short segment disease.

Hirschsprung disease is a condition characterized by the absence of nerve cells in certain parts of the colon, leading to problems with bowel movements. It is a congenital disorder that is present at birth. While Hirschsprung disease can occur in individuals with Down syndrome, the statement that it is more common in girls than in boys is incorrect. In fact, Hirschsprung disease is more commonly seen in boys than in girls.

Explanation

Hirschsprung disease is a condition characterized by the absence of nerve cells in certain parts of the colon, leading to problems with bowel movements. It is a congenital disorder that is present at birth. While Hirschsprung disease can occur in individuals with Down syndrome, the statement that it is more common in girls than in boys is incorrect. In fact, Hirschsprung disease is more commonly seen in boys than in girls.

12. Which statement is a prediction of the multifactorial threshold model?

An individual's risk is not altered by the number of affected first-degree relatives

The age of onset decreases when there are affected relatives in two previous generations

The differential risk to relatives of an affected proband increases as the disease prevalence decreases

Affected individuals almost always have an affected parent

The multifactorial threshold model suggests that the risk to relatives of an affected individual increases as the disease prevalence decreases. This means that if a disease is less common in the population, the risk to relatives of an affected individual is higher compared to a disease that is more common. This prediction is based on the idea that in a population with a lower disease prevalence, the genetic and environmental factors that contribute to the disease have a greater impact on the risk to relatives.

Explanation

The multifactorial threshold model suggests that the risk to relatives of an affected individual increases as the disease prevalence decreases. This means that if a disease is less common in the population, the risk to relatives of an affected individual is higher compared to a disease that is more common. This prediction is based on the idea that in a population with a lower disease prevalence, the genetic and environmental factors that contribute to the disease have a greater impact on the risk to relatives.

13. Given that G (effect due to genetics) = 0.50, E1 (effect due to individual differences) = 0.10, and E2 (effect due to familial differences) = 0.40, which of the following pairs of individuals will be most similar in ability to score high on an IQ test.

Siblings reared apart

Grandson - grandfather

Dizygotic twins reared together

Monozygotic twins reared apart

Dizygotic twins reared together will be most similar in ability to score high on an IQ test. This is because they share 50% of their genetic material (G), which contributes to their similarity in ability. Additionally, they are reared together, meaning they have similar environmental influences (E1 and E2). Therefore, the combination of genetic and environmental factors makes dizygotic twins reared together the most similar in ability to score high on an IQ test.

Explanation

Dizygotic twins reared together will be most similar in ability to score high on an IQ test. This is because they share 50% of their genetic material (G), which contributes to their similarity in ability. Additionally, they are reared together, meaning they have similar environmental influences (E1 and E2). Therefore, the combination of genetic and environmental factors makes dizygotic twins reared together the most similar in ability to score high on an IQ test.

14. In the P generation we crossed a red-flowered and white-flowered plant to get an F1 generation that was intermediate in color (pink) between the two parents. The F1s were then crossed to produce an F2. Which of the following will have the largest phenotypic variance?

The red-flowered P generation

The white-flowered P generation

The F1 generation

The F2 generation

The F1 generation will have the largest phenotypic variance because it is a result of crossing two parents with different phenotypes (red and white) which produces an intermediate phenotype (pink). This mixing of traits increases the variation in the F1 generation compared to the P generation or the F2 generation, where the traits may segregate and become more uniform.

Explanation

The F1 generation will have the largest phenotypic variance because it is a result of crossing two parents with different phenotypes (red and white) which produces an intermediate phenotype (pink). This mixing of traits increases the variation in the F1 generation compared to the P generation or the F2 generation, where the traits may segregate and become more uniform.

15. In a population of flies the mean bristle number was 6.4. Three pairs of flies were used as parents and their mean bristle number was 7.2. Their offspring had a mean bristle number of 7.0. What was the realized heritability?

0.75

0.25

0.91

0.86

The realized heritability can be calculated by dividing the difference in mean bristle number between the offspring and the population mean by the difference in mean bristle number between the parents and the population mean. In this case, the difference in mean bristle number between the offspring and the population mean is 7.0 - 6.4 = 0.6, and the difference in mean bristle number between the parents and the population mean is 7.2 - 6.4 = 0.8. Dividing 0.6 by 0.8 gives 0.75, which is the realized heritability.

Explanation

The realized heritability can be calculated by dividing the difference in mean bristle number between the offspring and the population mean by the difference in mean bristle number between the parents and the population mean. In this case, the difference in mean bristle number between the offspring and the population mean is 7.0 - 6.4 = 0.6, and the difference in mean bristle number between the parents and the population mean is 7.2 - 6.4 = 0.8. Dividing 0.6 by 0.8 gives 0.75, which is the realized heritability.

16. A measure of dispersion about the mean in a population is the

Covariance

Average

Correlation

Variance

Correlation is a measure of dispersion about the mean in a population. It quantifies the relationship between two variables and indicates how they vary together. A high correlation value indicates a strong relationship, while a low correlation value indicates a weak or no relationship. Therefore, correlation is a suitable measure of dispersion about the mean as it provides information about the extent to which data points deviate from the mean and how they are related to each other.

Explanation

Correlation is a measure of dispersion about the mean in a population. It quantifies the relationship between two variables and indicates how they vary together. A high correlation value indicates a strong relationship, while a low correlation value indicates a weak or no relationship. Therefore, correlation is a suitable measure of dispersion about the mean as it provides information about the extent to which data points deviate from the mean and how they are related to each other.