Quantitative genetics MCQ Quiz - Objective Question with Answer for Quantitative genetics - Download Free PDF
Last updated on Apr 1, 2025
Latest Quantitative genetics MCQ Objective Questions
Quantitative genetics Question 1:
Given below are statements on concepts of genetics.
A. The degree to which a particular gene is expressed in a phenotype is called ____________.
B. A heritable change in gene expression that does not result from a change in the nucleotide sequence of the genome is called ________ change.
C. The frequency with which a dominant or homozygous recessive gene is phenotypically expressed within a population is called ____________.
D. An allele that results in the death of organisms that is homozygous for the allele is ___________.
Which one of the following options represents the most appropriate sequence of terms to fill all the blank spaces in the above statements?
Answer (Detailed Solution Below)
Quantitative genetics Question 1 Detailed Solution
The correct answer is A - expressivity, B - epigenetic, C - penetrance, D - recessive lethal.
Explanation:
In genetics, the terms used to describe gene expression, heritable changes, and effects of alleles in phenotypes have precise meanings.
Statement A: "The degree to which a particular gene is expressed in a phenotype is called ____________."
- The degree of expression of a gene in a phenotype refers to expressivity, which describes how much the trait is expressed or how severe the phenotype is. Thus, the correct term for this blank is expressivity.
Statement B: "A heritable change in gene expression that does not result from a change in the nucleotide sequence of the genome is called ________ change."
- A heritable change in gene expression without any change in the nucleotide sequence is called an epigenetic change. Epigenetic changes involve mechanisms such as DNA methylation and histone modification that affect gene expression without altering the DNA sequence.
Statement C: "The frequency with which a dominant or homozygous recessive gene is phenotypically expressed within a population is called ____________."
- The frequency at which a gene is expressed in the phenotype is called penetrance, which refers to the proportion of individuals carrying a particular variant of a gene (allele) that also express an associated trait.
Statement D: "An allele that results in the death of organisms that is homozygous for the allele is ___________."
- An allele that causes death when present in the homozygous state is called a recessive lethal allele.
Key Points
- Expressivity refers to the degree or intensity of a gene's expression in the phenotype.
- Epigenetic change involves heritable modifications in gene expression without changes in the DNA sequence.
- Penetrance is the frequency with which a gene is expressed in the phenotype.
- A recessive lethal allele leads to death when the organism is homozygous for that allele.
Quantitative genetics Question 2:
The statements below are about possible genetic relatedness between individuals of a monogamous, haplodiploid insect.
A. A female is related to its son by 0.5
B. A female is related to its brother by 0.5
C. A male is related to its mother by 1
D. A male is related to its daughter by 1
Which one of the following options represents the combination of all correct statements?
Answer (Detailed Solution Below)
Quantitative genetics Question 2 Detailed Solution
The correct options are: A, C, and D
Explanation:
A. A female is related to its son by 0.5
- In haplodiploid systems, the mother (diploid) passes one set of her chromosomes to her son (haploid).
- Therefore, each son inherits half of his genes from his mother, making the genetic relatedness 0.5.
- This statement is correct.
B. A female is related to its brother by 0.5
- A diploid female receives half of her chromosomes from each parent. In a haplodiploid system, a male passes all his genes to his offspring.
- A female and her brother share the genes they inherit from their mother; brothers and sisters have a relatedness of 0.25 (due to the haplodiploid genetics), not 0.5.
- This statement is incorrect.
C. A male is related to its mother by 1
- A male (haploid) inherits all his genes from his mother (diploid) as he develops from an unfertilized egg.
- Thus, the male is related to his mother by 1.
- This statement is correct.
D. A male is related to its daughter by 1
- A male (haploid) passes all his genes to his daughter (diploid), who inherits all her chromosomes from her father and experiences recombination from her mother.
- Thus, the daughter carries all her father’s genes, but due to diploidy, the correct coefficient of relatedness is 0.5, not 1.
- In haplo-diploid system, male is related to its daughter by 1
Key Points
Haplodiploid System: In haplodiploid species, males are haploid (having one set of chromosomes) and females are diploid (having two sets of chromosomes).
Genetic Relatedness:
- Mother to Son: In haplodiploid species, a female passes one set of her chromosomes to her haploid son, resulting in a relatedness of 0.5.
- Male’s Relation to Mother: Since males inherit all their genes from their mother, the relatedness is 1.
- Male’s Relation to Daughter: A male passes all his genes to his daughter, making their genetic relatedness 0.5. (The statement D inaccurately states it as 1).
- Females and Brothers: In haplodiploid systems, females and their brothers share 1/4 (or 0.25) of their genes due to the common parent, but B inaccurately indicates 0.5.
Table: Shared gene proportions in haplo-diploid sex-determination system relationships
| Sex | Daughter | Son | Mother | Father | Sister | Brother |
| Female | 1/2 | 1/2 | 1/2 | 1/2 | 3/4 | 1/4 |
| Male | 1 | N/A | 1 | N/A | 1/2 | 1/2 |
Quantitative genetics Question 3:
In a plant species, the following pathways contribute to seed color. The wild-type phenotype of seed color is red.
• A recessive mutation of gene A leads to white color pigment.
• A recessive mutation of gene B leads to a transparent outer layer and the color of the seed is based on the color of the endosperm.
• The two genes are present on two different chromosomes.
• Often, a yellow or white colored seed has red spots.
Based on the above information, the following statements were made:
A. The probability of getting red-colored seeds from a dihybrid cross involving two heterozygous mutants is 9/16.
B. The mutation in gene B could have been caused by a transposable element.
C. A plant producing red seeds would breed true for the seed color.
Which one of the following options represents a combination of all correct statements?
Answer (Detailed Solution Below)
Quantitative genetics Question 3 Detailed Solution
The correct answer is B only
Explanation:
- Wild-Type Phenotype: The wild type of seed color is red, which indicates the presence of both yellow and red pigments due to the functioning of genes A and B.
- Gene A: A recessive mutation in gene A leads to a white color pigment. Thus, the wild-type A allele (A) is required for yellow pigment deposition in the endosperm.
- Gene B: A recessive mutation in gene B results in a transparent outer layer, indicating that the wild-type B allele (B) is necessary for red pigment deposition in the outer layer.
- Seed Color Determination: The final seed color is dependent on the color of the endosperm, which is determined by the activity of gene A and gene B.
A. The probability of getting red-colored seeds from a dihybrid cross involving two heterozygous mutants is 9/16.
- This statement is incorrect. The seed color in this case depends on the presence of at least one dominant allele from both genes A and B for red seeds. The calculation for a dihybrid cross involving complementary or supplementary genes does not lead to a straightforward 9/16 probability.
B. The mutation in gene B could have been caused by a transposable element.
- Transposable elements (TEs) can cause mutations in the genome, including insertions that can disrupt normal gene function. Therefore, a mutation in gene B could have been caused by such an element. Therefore, Statement B is correct.
C. A plant producing red seeds would breed true for the seed color.
- For a plant producing red seeds (A- B-), it can either be homozygous dominant (AABB) or heterozygous (AaBb). If the plant is heterozygous, it will not breed true because it can produce gametes with both dominant and recessive alleles, leading to a variety of offspring colors. Therefore, unless the plant is homozygous, it won't breed true.Therefore, Statement C is incorrect.
Quantitative genetics Question 4:
Mother and father of a person with ‘O’ blood group have ‘A’ and ‘B’ blood group respectively. What would be the genotype of both mother and father?
Answer (Detailed Solution Below)
Quantitative genetics Question 4 Detailed Solution
The correct answer is Both mother and father are heterozygous for ‘A’ and ‘B’ blood group, respectively
Concept:
- The ABO blood group system is determined by the presence of A and B alleles, with O being a recessive trait. For a person to have an O blood group, they must have two O alleles (genotype OO).
- A person with A blood group could have either genotype AA or AO, and a person with B blood group could have either genotype BB or BO.
Explanation:
- Mother is heterozygous for ‘A’ blood group and father is heterozygous for ‘B’: This is correct because the only way a child with OO blood group can be produced is if each parent provides an O allele. Hence, the mother must have an AO genotype and the father must have a BO genotype.
- Mother is homozygous for ‘A’ blood group and father is heterozygous for ‘B’: If the mother were homozygous AA, she could not contribute an O allele. Hence, this scenario would not result in an O blood group child.
- Both mother and father are homozygous for ‘A’ and ‘B’ blood group: If both were homozygous (AA and BB), they would only pass on A or B alleles and could not produce an O blood group child.
- Both mother and father are heterozygous for ‘A’ and ‘B’ blood group, respectively: This is the correct scenario because each parent can pass on an O allele, which is necessary for the child to have an OO genotype.
If mother and father of a person with 'O' blood group have 'A' and 'B' blood group then both mother and father will be heterozygous for 'A' and 'B' blood group respectively.
The progeny with genotype 'ii' will have 'O' blood group.
| Allele from Parent 1 | Allele from Parent 2 | Genotype of offspring | Blood types of offspring |
| IA | IA | IAIA | A |
| IA | IB | IAIB | AB |
| IA | i | IAi | A |
| IB | IA | IAIB | AB |
| IB | IB | IBIB | B |
| IB | i | IBi | B |
| i | i | ii | O |
Table: Table Showing the Genetic Basis of Blood Groups in Human Population.
Quantitative genetics Question 5:
Occasionally, a single gene may express more than one effect. The phenomenon is called:
Answer (Detailed Solution Below)
Quantitative genetics Question 5 Detailed Solution
The correct answer is pleiotropy
Concept:
- Pleiotropy refers to the phenomenon where a single gene influences multiple, seemingly unrelated traits or effects.
- A single gene can exhibit multiple phenotypic expression. Such a gene is called a pleiotropic gene.
- This occurs when one gene affects multiple physiological or developmental pathways, leading to a variety of outcomes in the organism.
- An example of this is the disease phenylketonuria, which occurs in humans. The disease is caused by mutation in the gene that codes for the enzyme phenyl alanine hydroxylase (single gene mutation). This manifests itself through phenotypic expression characterised by mental retardation and a reduction in hair and skin pigmentation.
Explanation:
- Pleiotropy: This describes the situation where a single gene affects multiple traits. For example, a mutation in a single gene may cause multiple symptoms in a genetic disorder.
- Multiple allelism: This involves a gene having more than two alleles in the population but does not necessarily result in multiple effects from a single gene.
- Mosaicism: This refers to the presence of two or more genetically different cell lines within the same individual, usually due to mutations occurring during development, rather than a single gene affecting multiple traits.
- Polygeny: This involves multiple genes contributing to a single trait, such as height or skin color, rather than a single gene affecting multiple traits.
Top Quantitative genetics MCQ Objective Questions
The statements below are about possible genetic relatedness between individuals of a monogamous, haplodiploid insect.
A. A female is related to its son by 0.5
B. A female is related to its brother by 0.5
C. A male is related to its mother by 1
D. A male is related to its daughter by 1
Which one of the following options represents the combination of all correct statements?
Answer (Detailed Solution Below)
Quantitative genetics Question 6 Detailed Solution
Download Solution PDFThe correct options are: A, C, and D
Explanation:
A. A female is related to its son by 0.5
- In haplodiploid systems, the mother (diploid) passes one set of her chromosomes to her son (haploid).
- Therefore, each son inherits half of his genes from his mother, making the genetic relatedness 0.5.
- This statement is correct.
B. A female is related to its brother by 0.5
- A diploid female receives half of her chromosomes from each parent. In a haplodiploid system, a male passes all his genes to his offspring.
- A female and her brother share the genes they inherit from their mother; brothers and sisters have a relatedness of 0.25 (due to the haplodiploid genetics), not 0.5.
- This statement is incorrect.
C. A male is related to its mother by 1
- A male (haploid) inherits all his genes from his mother (diploid) as he develops from an unfertilized egg.
- Thus, the male is related to his mother by 1.
- This statement is correct.
D. A male is related to its daughter by 1
- A male (haploid) passes all his genes to his daughter (diploid), who inherits all her chromosomes from her father and experiences recombination from her mother.
- Thus, the daughter carries all her father’s genes, but due to diploidy, the correct coefficient of relatedness is 0.5, not 1.
- In haplo-diploid system, male is related to its daughter by 1
Key Points
Haplodiploid System: In haplodiploid species, males are haploid (having one set of chromosomes) and females are diploid (having two sets of chromosomes).
Genetic Relatedness:
- Mother to Son: In haplodiploid species, a female passes one set of her chromosomes to her haploid son, resulting in a relatedness of 0.5.
- Male’s Relation to Mother: Since males inherit all their genes from their mother, the relatedness is 1.
- Male’s Relation to Daughter: A male passes all his genes to his daughter, making their genetic relatedness 0.5. (The statement D inaccurately states it as 1).
- Females and Brothers: In haplodiploid systems, females and their brothers share 1/4 (or 0.25) of their genes due to the common parent, but B inaccurately indicates 0.5.
Table: Shared gene proportions in haplo-diploid sex-determination system relationships
| Sex | Daughter | Son | Mother | Father | Sister | Brother |
| Female | 1/2 | 1/2 | 1/2 | 1/2 | 3/4 | 1/4 |
| Male | 1 | N/A | 1 | N/A | 1/2 | 1/2 |
Given below are statements on concepts of genetics.
A. The degree to which a particular gene is expressed in a phenotype is called ____________.
B. A heritable change in gene expression that does not result from a change in the nucleotide sequence of the genome is called ________ change.
C. The frequency with which a dominant or homozygous recessive gene is phenotypically expressed within a population is called ____________.
D. An allele that results in the death of organisms that is homozygous for the allele is ___________.
Which one of the following options represents the most appropriate sequence of terms to fill all the blank spaces in the above statements?
Answer (Detailed Solution Below)
Quantitative genetics Question 7 Detailed Solution
Download Solution PDFThe correct answer is A - expressivity, B - epigenetic, C - penetrance, D - recessive lethal.
Explanation:
In genetics, the terms used to describe gene expression, heritable changes, and effects of alleles in phenotypes have precise meanings.
Statement A: "The degree to which a particular gene is expressed in a phenotype is called ____________."
- The degree of expression of a gene in a phenotype refers to expressivity, which describes how much the trait is expressed or how severe the phenotype is. Thus, the correct term for this blank is expressivity.
Statement B: "A heritable change in gene expression that does not result from a change in the nucleotide sequence of the genome is called ________ change."
- A heritable change in gene expression without any change in the nucleotide sequence is called an epigenetic change. Epigenetic changes involve mechanisms such as DNA methylation and histone modification that affect gene expression without altering the DNA sequence.
Statement C: "The frequency with which a dominant or homozygous recessive gene is phenotypically expressed within a population is called ____________."
- The frequency at which a gene is expressed in the phenotype is called penetrance, which refers to the proportion of individuals carrying a particular variant of a gene (allele) that also express an associated trait.
Statement D: "An allele that results in the death of organisms that is homozygous for the allele is ___________."
- An allele that causes death when present in the homozygous state is called a recessive lethal allele.
Key Points
- Expressivity refers to the degree or intensity of a gene's expression in the phenotype.
- Epigenetic change involves heritable modifications in gene expression without changes in the DNA sequence.
- Penetrance is the frequency with which a gene is expressed in the phenotype.
- A recessive lethal allele leads to death when the organism is homozygous for that allele.
Wheat plants can have kernels of white colour or in shades of red i.e. light red, red, dark red and very dark red (purple).
A researcher made the following cross:
|
P |
wheat plants with white kernels |
X |
wheat plants with purple (very dark red) kernels |
|
|
F1 |
All plants with red kernels |
|
||
|
F2 |
1/16 |
Plants with purple kernels |
|
|
|
|
4/16 |
Plants with dark red kernels |
|
|
|
|
6/16 |
Plants with red kernels |
|
|
|
|
4/16 |
Plants with light red kernels |
|
|
|
|
1/16 |
Plants with white kernels |
|
|
The following conclusions are made from the results obtained:
A. It is a dihybrid cross where white colour is coded by gene A and the purple colour is coded by gene B
B. Two genes, both coding for the colour of kernel and each gene having two alleles, one that produced red pigment and the other that produced no pigment.
C. Four genes, one coding for no pigment, which is epistatic over the other genes. The remaining three genes have 2 alleles each, one that produced red pigment and the other that produced no pigment.
D. The trait is influenced by the environment leading to the observed variation in kernel colour.
Which of the above conclusion(s) is/are correct?
Answer (Detailed Solution Below)
Quantitative genetics Question 8 Detailed Solution
Download Solution PDFThe correct answer is Option 2 i.e. B only
Concept:
- Each dominant allele expresses a portion or unit of the trait, with the whole trait only manifesting when all the dominant alleles are present. It is the inheritance controlled by one or more genes.
- Unlike qualitative traits, which can be altered in different ways by the environment, quantitative traits are typically governed by many factors or genes (possibly 10 or 100 or more), each of which contributes so little to the phenotype that their individual effects cannot be detected using Mendelian methods but only statistical ones.
- Polygenes, also known as cumulative genes, are such non-allelic genes that influence the phenotype of a single quantitative trait.
Explanation:
Statement A:- INCORRECT
- White and purple is not due to individual effects of A and B gens but due to a mixture of these two genes.
Statement B:- CORRECT
- AABB x aabb
↓
- AaBb x AaBb
- F2 ratio= ?
- In quantitative inheritance, phenotype depends on no. of dominant alleles.
- There is a total of four alleles, two of A (Aa) and two of B (Bb), there will be a total of five phenotypes.
- The given ratio is 1:4:6:4:1.
- Hence, to determine the no. of genes, the formula used is 1/4^n, where 1/4^n is 1/16, due to which n is 2.
Statement C:- INCORRECT
- There is a total of four alleles, two of A (Aa) and two of B (Bb), there will be a total of five phenotypes.
Statement D:- INCORRECT
- There is not much variation due to the environment in quantitative inheritance.
Quantitative genetics Question 9:
Two varieties of maize averaging 48 and 72 inches in height, respectively, are crossed. The F1 progeny is quite uniform averaging 60 inches in height. Of the 500 F2 plants, the shortest 2 are 48 inches and the tallest 2 are 72 inches. What is the probable number of polygenes involved in this trait?
Answer (Detailed Solution Below)
Quantitative genetics Question 9 Detailed Solution
Concept:
- Numerous alleles found in various loci are responsible for the inheritance of numerous phenotypic characteristics and traits found in plants and animals, including height, skin pigmentation, hair and eye colour, and the production of milk and eggs. The term "polygenic inheritance" describes this.
Explanation:
- In 1908 Nilsson Ehle presented the multiple factor hypothesis to explain his result on the inheritance of seed colour in wheats and maize.
- In crosses showing 15 ∶ 1 ratio in F2 seed colour is governed by two gene.
- 63 ∶ 1 ratio is governed by 3 genes. So, the 498 ∶ 2 or 249 ∶ 1 ratio will probably be governed by four genes.
The probable number of polygenes (additive genes) involved in the height trait of maize, we can use the following quantitative genetics formula:
\(\text{Number of genes (n)} = \frac{(P1 - P2)^2}{8 \times V}\)
Where:
- P1 and P2 are the parental heights
- V is the variance in the F2 population
Assuming that each allele contributes equally and additively to the trait, and since the height range is fairly evenly distributed between the two extremes, we can make some basic assumptions and simplifications to approximate the number of polygenes.
Here is the breakdown step-by-step:
Identify the parental heights (P1 and P2):
- P1 = 48 inches
- P2 = 72 inches
- Mean height of the F1 progeny = 60 inches
Determine the range of phenotypes in the F2 generation:
- Shortest plants = 48 inches
- Tallest plants = 72 inches
- Range (R) = 72 - 48 = 24 inches
Use the formula for estimating the number of polygenes:\(N = \left( \frac{R}{2} \right)^2\) .
- Since R = 24
- \(N = \left( \frac{24}{2} \right)^2 \)
- \( N = 12^2\)
- N = 144
Quantitative genetics Question 10:
Which of the following features is not a quantitative trait:
Answer (Detailed Solution Below)
Quantitative genetics Question 10 Detailed Solution
Concept:
- A quantitative trait is a measurable phenotype that depends on the cumulative actions of many genes and the environment.
- These traits can vary among individuals, over a range, to produce a continuous distribution of phenotypes.
- The quantitative traits, however, are economically important measurable phenotypic traits of degree such as height, weight, skin pigmentation, susceptibility to pathological diseases or intelligence in man; amount of flowers, fruits, seeds, milk, meat or egg produced by plants or animals, etc.
- Examples include height, weight and blood pressure.
Explanation:
Characteristics of quantitative traits
- polygenic
- may show either a continuous distribution or have discrete classes (meristic)
- continuous - height, weight, intelligence, etc.
- discrete - fertile/sterile, diseased/normal, # of eggs, etc. Despite the discrete character the trait is determined by an underlying continuous distribution
3. affected by environmental factors
4. genetic model: additive genes
- multiple genes effect the trait
- each gene has two alleles
- one allele adds to the trait
- the other allele does not add to the trait
5. alleles from different genes have the same effect on the trait
6.the amount of the trait is determined by the total number of additive alleles at all of the different genes plus a contribution from the environment.
- simple example, red coloring of wheat kernals, simple because their is very little environmental effect
two genes, A and B with two alleles each, A, a, B, b
Hence the correct answer is option 4Quantitative genetics Question 11:
The statements below are about possible genetic relatedness between individuals of a monogamous, haplodiploid insect.
A. A female is related to its son by 0.5
B. A female is related to its brother by 0.5
C. A male is related to its mother by 1
D. A male is related to its daughter by 1
Which one of the following options represents the combination of all correct statements?
Answer (Detailed Solution Below)
Quantitative genetics Question 11 Detailed Solution
The correct options are: A, C, and D
Explanation:
A. A female is related to its son by 0.5
- In haplodiploid systems, the mother (diploid) passes one set of her chromosomes to her son (haploid).
- Therefore, each son inherits half of his genes from his mother, making the genetic relatedness 0.5.
- This statement is correct.
B. A female is related to its brother by 0.5
- A diploid female receives half of her chromosomes from each parent. In a haplodiploid system, a male passes all his genes to his offspring.
- A female and her brother share the genes they inherit from their mother; brothers and sisters have a relatedness of 0.25 (due to the haplodiploid genetics), not 0.5.
- This statement is incorrect.
C. A male is related to its mother by 1
- A male (haploid) inherits all his genes from his mother (diploid) as he develops from an unfertilized egg.
- Thus, the male is related to his mother by 1.
- This statement is correct.
D. A male is related to its daughter by 1
- A male (haploid) passes all his genes to his daughter (diploid), who inherits all her chromosomes from her father and experiences recombination from her mother.
- Thus, the daughter carries all her father’s genes, but due to diploidy, the correct coefficient of relatedness is 0.5, not 1.
- In haplo-diploid system, male is related to its daughter by 1
Key Points
Haplodiploid System: In haplodiploid species, males are haploid (having one set of chromosomes) and females are diploid (having two sets of chromosomes).
Genetic Relatedness:
- Mother to Son: In haplodiploid species, a female passes one set of her chromosomes to her haploid son, resulting in a relatedness of 0.5.
- Male’s Relation to Mother: Since males inherit all their genes from their mother, the relatedness is 1.
- Male’s Relation to Daughter: A male passes all his genes to his daughter, making their genetic relatedness 0.5. (The statement D inaccurately states it as 1).
- Females and Brothers: In haplodiploid systems, females and their brothers share 1/4 (or 0.25) of their genes due to the common parent, but B inaccurately indicates 0.5.
Table: Shared gene proportions in haplo-diploid sex-determination system relationships
| Sex | Daughter | Son | Mother | Father | Sister | Brother |
| Female | 1/2 | 1/2 | 1/2 | 1/2 | 3/4 | 1/4 |
| Male | 1 | N/A | 1 | N/A | 1/2 | 1/2 |
Quantitative genetics Question 12:
Given below are statements on concepts of genetics.
A. The degree to which a particular gene is expressed in a phenotype is called ____________.
B. A heritable change in gene expression that does not result from a change in the nucleotide sequence of the genome is called ________ change.
C. The frequency with which a dominant or homozygous recessive gene is phenotypically expressed within a population is called ____________.
D. An allele that results in the death of organisms that is homozygous for the allele is ___________.
Which one of the following options represents the most appropriate sequence of terms to fill all the blank spaces in the above statements?
Answer (Detailed Solution Below)
Quantitative genetics Question 12 Detailed Solution
The correct answer is A - expressivity, B - epigenetic, C - penetrance, D - recessive lethal.
Explanation:
In genetics, the terms used to describe gene expression, heritable changes, and effects of alleles in phenotypes have precise meanings.
Statement A: "The degree to which a particular gene is expressed in a phenotype is called ____________."
- The degree of expression of a gene in a phenotype refers to expressivity, which describes how much the trait is expressed or how severe the phenotype is. Thus, the correct term for this blank is expressivity.
Statement B: "A heritable change in gene expression that does not result from a change in the nucleotide sequence of the genome is called ________ change."
- A heritable change in gene expression without any change in the nucleotide sequence is called an epigenetic change. Epigenetic changes involve mechanisms such as DNA methylation and histone modification that affect gene expression without altering the DNA sequence.
Statement C: "The frequency with which a dominant or homozygous recessive gene is phenotypically expressed within a population is called ____________."
- The frequency at which a gene is expressed in the phenotype is called penetrance, which refers to the proportion of individuals carrying a particular variant of a gene (allele) that also express an associated trait.
Statement D: "An allele that results in the death of organisms that is homozygous for the allele is ___________."
- An allele that causes death when present in the homozygous state is called a recessive lethal allele.
Key Points
- Expressivity refers to the degree or intensity of a gene's expression in the phenotype.
- Epigenetic change involves heritable modifications in gene expression without changes in the DNA sequence.
- Penetrance is the frequency with which a gene is expressed in the phenotype.
- A recessive lethal allele leads to death when the organism is homozygous for that allele.
Quantitative genetics Question 13:
Mother and father of a person with ‘O’ blood group have ‘A’ and ‘B’ blood group respectively. What would be the genotype of both mother and father?
Answer (Detailed Solution Below)
Quantitative genetics Question 13 Detailed Solution
The correct answer is Both mother and father are heterozygous for ‘A’ and ‘B’ blood group, respectively
Concept:
- The ABO blood group system is determined by the presence of A and B alleles, with O being a recessive trait. For a person to have an O blood group, they must have two O alleles (genotype OO).
- A person with A blood group could have either genotype AA or AO, and a person with B blood group could have either genotype BB or BO.
Explanation:
- Mother is heterozygous for ‘A’ blood group and father is heterozygous for ‘B’: This is correct because the only way a child with OO blood group can be produced is if each parent provides an O allele. Hence, the mother must have an AO genotype and the father must have a BO genotype.
- Mother is homozygous for ‘A’ blood group and father is heterozygous for ‘B’: If the mother were homozygous AA, she could not contribute an O allele. Hence, this scenario would not result in an O blood group child.
- Both mother and father are homozygous for ‘A’ and ‘B’ blood group: If both were homozygous (AA and BB), they would only pass on A or B alleles and could not produce an O blood group child.
- Both mother and father are heterozygous for ‘A’ and ‘B’ blood group, respectively: This is the correct scenario because each parent can pass on an O allele, which is necessary for the child to have an OO genotype.
If mother and father of a person with 'O' blood group have 'A' and 'B' blood group then both mother and father will be heterozygous for 'A' and 'B' blood group respectively.
The progeny with genotype 'ii' will have 'O' blood group.
| Allele from Parent 1 | Allele from Parent 2 | Genotype of offspring | Blood types of offspring |
| IA | IA | IAIA | A |
| IA | IB | IAIB | AB |
| IA | i | IAi | A |
| IB | IA | IAIB | AB |
| IB | IB | IBIB | B |
| IB | i | IBi | B |
| i | i | ii | O |
Table: Table Showing the Genetic Basis of Blood Groups in Human Population.
Quantitative genetics Question 14:
In a three point cross, a recombination event produces the following:
6 Double crossovers
142 Single crossovers
352 Parental genotypes
What would be the percentage recombination between the terminal genes?
Answer (Detailed Solution Below)
Quantitative genetics Question 14 Detailed Solution
The correct answer is 30.8%
Explanation:
- In genetic mapping, a three-point cross is used to determine the order and distance between three genes on a chromosome.
- Recombination frequency is calculated by observing the offspring phenotypes and determining the proportion of recombinant offspring.
Recombination events include single crossovers and double crossovers, and these events help to map the relative positions of genes on chromosomes.
- Parental genotypes: These are the offspring that retain the original combination of alleles from the parents. In this problem, there are 352 parental genotypes.
- Single crossovers: These occur when there is an exchange of genetic material between homologous chromosomes at one point. There are 142 single crossovers in this case.
- Double crossovers: These occur when there are two exchanges of genetic material between homologous chromosomes. There are 6 double crossovers in this problem.
Total number of offspring: The total number of offspring is the sum of parental genotypes, single crossovers, and double crossovers. Therefore, the total is 352 + 142 + 6 = 500.
Number of recombination events = SCOs (142) + 2 × DCOs (6)
= 142 + 12
= 154 recombination events
Total offspring = 500
Recombination frequency:
Percentage recombination = (Number of recombination events / Total number of offspring) × 100
= (154 / 500) × 100
= 30.8%
Quantitative genetics Question 15:
The figure below depicts a hypothetical scheme for synthesizing a target product in plants. Ⓐ, Ⓑ, and Ⓒ are the precursors of a target product Ⓓ, whereas Ⓔ is a by‐product. The key enzymes of the pathway are indicated as E1–E6. To enhance the levels of target product Ⓓ, following strategies were tested:
A. Enhancing the activity of the enzyme E5 by over‐expression and/or protein engineering.
B. Enhancing the activity of the enzyme E4 by over‐expression and/or protein engineering.
C. Enhancing the levels of Ⓒ.
D. Blocking the activity of E6 by RNA‐interference or CRISPR/Cas‐mediated knockout.
Which of the above mentioned strategies are likely to provide the maximum enhancement of the target product compared to the by‐product, if no feedback regulation exists for any of the enzymes in the pathway?
Answer (Detailed Solution Below)
Quantitative genetics Question 15 Detailed Solution
The correct answer is Option 4 i.e. A and D
Explanation-
A. Enhancing the activity of the enzyme E5:
This strategy involves increasing the activity of the enzyme responsible for converting precursor Ⓒ to the target product Ⓓ. If successful, it can lead to higher levels of the target product.
B. Enhancing the activity of the enzyme E4:
Enhancing the activity of E4 might result in increased production of Ⓑ, but it may not necessarily lead to a significant increase in the target product Ⓓ.
C. Enhancing the levels of Ⓒ:
Increasing the levels of Ⓒ might lead to a proportional increase in Ⓓ, but it might also result in increased production of the by-product Ⓔ.
D. Blocking the activity of E6:
Inhibiting E6 can prevent the conversion of Ⓒ to Ⓔ, resulting in an accumulation of Ⓓ.
Conclusion-Considering the absence of feedback regulation, strategies A and D are likely to be the most effective.
By enhancing the activity of the enzyme (E5) responsible for converting Ⓒ to Ⓓ and blocking the activity of the enzyme (E6) involved in the conversion of Ⓒ to Ⓔ, you can maximize the production of the target product Ⓓ compared to the by-product Ⓔ.