Genetics - Problem Drill 09: Genetics and Environment No. 1 of 10 1. Heritability is. (A) The fraction of a population's phenotype, which is strictly due to genetic factors. (B) The fraction of a population's phenotypic variation that is strictly due to genetic factors. (C) The degree to which related members of a population resemble each another. (D) The degree to which a continuously varying trait is controlled by genotype. (E) All phenotypic plasticity. By definition, heritability is the proportion of genetic factors contributing to a phenotype within a group of individuals in a certain environment. B. Correct! This is the definition of heritability. Resemblance is not described by heritability. Heritability always refers to a group, not to a trait. Heritability is the genetic fraction, excluding environment and the interaction between genes and environment which, taken together, comprise all the phenotype components. Heritability is a concept that is easily confused, so memorize the definition. (B)The fraction of a population's phenotypic variation that is strictly due to genetic factors.
No. 2 of 10 2. Retinoblastoma is a childhood retinal tumor, caused by a mutant Rb gene. Heterozygous would display the disease at a penetrance of 90%. Bob had this tumor when he was a child but he survived by surgical removal of the tumor. What is the chance of his children getting the disease? (A) 90% (B) 45% (C) 25% (D) 10% (E) 0% Bob is heterozygous; that means his genotype is Rb+/-. His children cannot have 100% of chance of inheriting the mutant allele. B. Correct! Bob is Rb+/-. His children will have 50% of chance of inheriting the mutant allele from him. Even the child getting the mutant allele would have 90% of chance of developing the disease; therefore, the probability of the child having the disease would be 50% * 90% = 45%. There is no way to get a 25% answer in this case. It is not possible to get a 10% in genetics of this disease in this case. Retinoblastoma is a dominant trait; his children have a chance of developing the disease. Some mutant genes have high penetrance (like Rb) but others may have relatively low penetrance (10-20%). This is used in genetic counseling to calculate the risk. (B) 45%
No. 3 of 10 3. Which of the following factors may NOT affect phenotype expression? (A) Temperature (B) Genetic composition (C) Food (D) Birth order (E) All of the above Temperature can affect phenotype expression, especially true for some temperature-sensitive strains. Genetic composition is always important for phenotype expression. Food (nutrition) can significantly affect phenotype expression. For example, when food is limited, people may develop poorly and their height may be stunted. D. Correct! Birth order does not belong to either genetic or environmental category; it does not affect phenotype expression. Temperature, genetic composition and food belong to either genetic or environmental factors; they do affect phenotype expression. Keep this in mind: Phenotype = genotype + environment (D)Birth order
No. 4 of 10 4. Which of the following statements is NOT true? (A) Heritability is specific to the population and environment. (B) Heritability measures the proportion of the phenotypic variance that is the result of genetic factors. (C) Heritability can predict an individual s phenotype based on its genotype. (D) Heritability is not all about additive genes. (E) Narrow-sense heritability is often used in calculating the response to selection. This statement is true; heritability is specific to the population and environment. If either changes, heritability may change too. This statement is true; this is the definition for heritability. C. Correct! Heritability predicts a population s phenotype instead of an individual s. This statement is true because heritability may also include dominant genes and interacting genes. This statement is true; the formula for calculating selection response includes h 2. Heritability refers to populations, not to individuals. (C)Heritability can predict an individual s phenotype based on its genotype.
No. 5 of 10 5. A red flower is crossed to a white flower, F1 is all red. F1 self-crosses to generate F2, which have 38 red, 24 pink, and 4 white. What is the most likely inheritance pattern of this trait? --Assume both parents are true inbred lines. (A) The trait is controlled by one gene, co-dominant inheritance. (B) The trait is controlled by one gene, normal Mendelian inheritance. (C) The trait is controlled by two genes with additive effect, normal Mendelian inheritance. (D) The trait is controlled by two genes with epistatic effect. (E) The trait is controlled by one gene with normal dominant and recessive trait. For co-dominance, all F1 should have pink flowers; this does not fit the data. One gene in normal Mendelian inheritance would give F1 being all red (if red is dominant) or all white (if white is dominant). C. Correct! Two-gene inheritance, if dissected into details, can be written as AaBb x AaBb; the F2 should be 9 A_B_, 3 aab_, 3 A_bb, and 1 aabb. Any of the A_B_ genotype would give red phenotype, while both aab_ and A_bb give pink (additive effect of A and B), aabb give white phenotype. The ratio in phenotype should then be red:pink:white = 9:6:1, which roughly fit into the data. In two-gene inheritance with epistasis, there would be no intermediate phenotype and there would be a modified ratio of F2. A third phenotype appeared in F1; this is apparently not a normal dominantrecessive trait relationship. Distinguish the difference among expressivity, penetrance, co-dominance and multiple gene inheritance. (C)The trait is controlled by two genes with additive effect, normal Mendelian inheritance.
No. 6 of 10 6. Nature theory. (A) Refers to genes and states that people behave according to their genetic predispositions. (B) Refers to nature and states that people behave according to their natural environment. (C) Does not depend on an individual s genetic makeup. (D) Involves learned behaviors that come from parental training. (E) States that an individual s genetics change based on their animal instincts. A. Correct! Nature theory refers to genes and states that people behave according to their genetic predispositions. Nature theory refers to genes and states that people behave according to their genetic predispositions. It is an individual s genetic makeup that instills the genetic predispositions. The belief that people act based on what they have been taught is part of the nurture theory. Nature theory states that an individual s genetics drive their behavior. Nature refers to genes. And the nature theory states that people behave according to their genetic predispositions or even animal instincts. Nurture refers to environment. The nurture theory refers to the belief that people think and behave in certain ways because they are taught to do so. (A)Refers to genes and states that people behave according to their genetic predispositions.
No. 7 of 10 7. What is meant by broad sense heritability? (A) It is a description of a single phenotypic variation due to genetic effects. (B) When broad sense heritability is calculated to less than 1, all of the variation in phenotype results from genetic difference. (C) When broad sense heritability is calculated to be equal to 0.5, all of the variation in phenotype results from genetic difference. (D) Broad sense heritability reflects the importance of genes producing the differences. (E) Broad sense heritability reflects the fact that genes never produce the differences seen in phenotypic variance. Broad sense heritability encompasses the total phenotypic variation. When broad sense heritability is calculated to be equal to 1, all of the variation in phenotype results from genetic difference. When broad sense heritability is calculated to be equal to 1, all of the variation in phenotype results from genetic difference. D. Correct! Broad sense heritability reflects the importance of genes producing the differences. Broad sense heritability reflects the importance of genes producing the differences. The purpose for breaking down VP (phenotypic variance) is to determine how much variance in a phenotype is due to genetics vs. environment. H2 is called broad sense heritability. This is used to describe the proportion of the total phenotypic variation due to genetic effects. It reflects the importance of genes in producing the difference. H 2 = Total genetic variance / Phenotypic variance = VG/ VP = V A + V D + V I --------------- V P (D)Broad sense heritability reflects the importance of genes producing the differences.
No. 8 of 10 8. Which of the following statements about calculating heritability is true? (A) Heritability calculations depend on comparing only unrelated individuals. (B) Both related and unrelated individuals are used for comparison in heritability calculations. (C) If genes are important, closely related individuals will have a less similar phenotype. (D) Heritability calculations depend on a completely different environment for all individuals. (E) The environment of the individuals in a heritability calculation plays no role. Heritability calculations depend on comparing related and unrelated individuals. B. Correct! Heritability calculations depend on comparing related and unrelated individuals. If genes are important, closely related individuals will have a more similar phenotype. Heritability calculations depend on a similar environment for all individuals. Heritability calculations depend on a similar environment for all individuals. The principle involved in the calculation of heritability is based on the comparison of related and unrelated individuals. If genes are important, closely related individuals will have a more similar phenotype. If environment is more important, phenotype is similar among related or unrelated individuals. This does require a similar environment for all individuals. The method used is Parent-offspring regression analysis. (B)Both related and unrelated individuals are used for comparison in heritability calculations.
No. 9 of 10 9. In genetics, penetrance. (A) Describes the probability of showing a certain phenotype given a certain genotype. (B) Penetrance describes the probability of showing a certain genotype given a certain phenotype. (C) Of 100%, it means that the phenotype is usually expressed. (D) Of 100%, it means that the phenotype is never expressed. (E) Is not dependent on an individual s genetic makeup. A. Correct! In genetic, penetrance describes the probability of showing a certain phenotype given a certain genotype. Penetrance describes visible phenotypes, not the individual s genetic makeup. In genetics, a penetrance of 100% means that the phenotype is always expressed. In genetics, a penetrance of 100% means that the phenotype is always expressed. The percentage of phenotypic expression depends, in part, on an individual s genetic makeup. Sometimes, a given genotype does not result in the expected phenotype. Penetrance is the probability of showing a phenotype given a certain genotype. A 100% penetrance means that the phenotype is always expressed. (A)Describes the probability of showing a certain phenotype given a certain genotype.
No. 10 of 10 10. Which of the following statements about expressivity is correct? (A) Expressivity describes the extent to which a certain gene is present in the genome of an individual. (B) Expressivity is independent of an individual s phenotype. (C) For example, if all 10 frogs in a group have at least 1 webbed foot, then the expressivity is said to be 100% in this case. (D) For example, if all 10 frogs in a group have at least 1 webbed foot, then both expressivity and penetrance would be 100%. (E) As long as all the individuals in a group had the same genotype, then they will always express the phenotype to a maximum level. Expressivity describes the extent to which a certain phenotype is expressed, given a certain genotype. The extent of phenotypic expression is the meaning or expressivity. For this example, all frogs would have to have all webbed feet for complete or 100% expressivity. D. Correct! While all frogs showed the phenotype, the extent to which they showed it is not 100%. While a certain genotype can predict whether or not a phenotype is expressed, the extent of phenotypic variation can vary in individuals with the same genotype. Expressivity is the variation of the expressed phenotype of a specific genotype. Expressivity varies from 0-100%. Penetrance = 9/9 = 100 % (all individual have expected phenotype. (D)For example, if all 10 frogs in a group have at least 1 webbed foot, then both expressivity and penetrance would be 100%.