GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Molecular Biology and Genetics

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #6 : Help With Hardy Weinberg

Within his rat population, a scientist is trying to generate twice as many recessive homozygotes as heterozygotes. What allelic frequency would accomplish this?

Possible Answers:

Correct answer:

Explanation:

Use the Hardy-Weinberg equations:

The equation he will need to set up is the following:

Solve for  and substitute the first equation into the equation above.

Simplify.

Lastly, find .

Example Question #1 : Help With Hardy Weinberg

Assuming Hardy-Weinberg equilibrium conditions, what are the heterozygote (Bb) and homozygote recessive (bb) genotypes for a gene if the homozygote dominant (BB) genotype is 0.45?

Possible Answers:

Cannot be determined

Bb = 0.15

bb = 0.4

Bb = 0.4

bb = 0.15

Bb = 0.11

bb = 0.44

Bb = 0.44

bb = 0.11

Correct answer:

Bb = 0.44

bb = 0.11

Explanation:

The correct answer is Bb = 0.44 and bb = 0.11. 

Since we know BB = 0.45 and the equations for allele frequencies when Hardy-Weinberg equilibrium conditions are met: 

and 

We solve for B first:

Now we can solve for the homozygote recessive.

Lastly, solve for the heterozygote.

 

Example Question #4 : Help With Hardy Weinberg

Which of the following is not an assumption of the Hardy-Weinberg equilibrium?

Possible Answers:

No natural selection within a population 

No mutations within a population

No gene flow between populations

No genetic drift within a population

Non-random mating within a population

Correct answer:

Non-random mating within a population

Explanation:

Non-random mating is not an assumption of the Hardy-Weinberg equilibrium, in fact, in order to make predictions about the next generation, random mating must be assumed. Additionally, no new mutations, no gene flow, no genetic drift, and no natural selection must also occur. If any of these phenomenon are present in a population, we can not estimate allele frequencies in subsequent generations due to chance, rather selective pressures may favor one allele over another allele. 

Example Question #11 : Inheritance

What are the phenotypic ratios for a given population for which the proportion of the dominant allele is 0.55 and that of the recessive allele is 0.45? 

Possible Answers:

Homozygous dominant: 0.25

Heterozygous: 0.50

Homozygous recessive: 0.25

Homozygous dominant: 0.30

Heterozygous: 0.20

Homozygous recessive: 0.50 

Homozygous dominant: 0.20

Heterozygous: 0.50

Homozygous recessive: 0.30 

Homozygous dominant: 0.50

Heterozygous: 0.30

Homozygous recessive: 0.20 

Homozygous dominant: 0.30

Heterozygous: 0.50

Homozygous recessive: 0.20 

Correct answer:

Homozygous dominant: 0.30

Heterozygous: 0.50

Homozygous recessive: 0.20 

Explanation:

To solve this problem, assume Hardy-Weinberg equilibrium and use the associated equations to solve:

   

 is dominant allele and  is recessive allele 

To find the phenotype ratios:

 homozygous dominant 

 heterozygous 

 homozygous recessive 

Example Question #31 : Molecular Biology And Genetics

Which of the following is not a tenet of Hardy-Weinberg equilibrium?

Possible Answers:

Randomized mating

No migration

Large population

No natural selection

Genetic drift

Correct answer:

Genetic drift

Explanation:

The Hardy-Weinberg equilibrium does not account for genetic drift. The Hardy-Weinberg law states that genetic frequencies will remain constant in a population from generation to generation in the absence of evolutionary influences. Therefore, there is no migration, natural selection, nonrandom mating, or small populations in a Hardy-Weinberg population.

Example Question #32 : Molecular Biology And Genetics

Which of the following are examples of codominance?

I. A person with blood type AB

II. A flower that displays a red and white spotted phenotype (both colors are attributed to the same gene; homozygosity for either color makes a flower that is completely red or white)

III. A flower that displays a pink phenotype (a homozygous dominant flower is red and a homozygous recessive flower is white)

IV. An organism whose heterozygous phenotype is identical to the homozygous dominant phenotype

Possible Answers:

I, II, and III

I and II

III and IV

IV only

Correct answer:

I and II

Explanation:

Codominance occurs when both phenotypes are displayed equally and independently in the phenotype (without blending). This is the case with blood type and the red and white spotted flower. A person with blood type AB expresses proteins that will recognize both type A and type B. The red and white spotted flower equally expresses the two color phenotypes.

The pink flower is an example of incomplete dominance (blended phenotype). Option IV describes a normal dominant-recessive hierarchy, where only one copy of the dominant allele is needed to display the dominant phenotype.

Example Question #2 : Help With Other Inheritance Patterns

When the expression and subsequent phenotype of one gene is dependent on the expression of another gene, this type of phenonemon is known as __________.

Possible Answers:

codominance

gene masking 

complete dominance

epistasis

incomplete dominance 

Correct answer:

epistasis

Explanation:

The correct answer is epistasis. Complete dominance, codominance, and incomplete dominance describe the expression of only one gene (one set of alleles) that do not depend on the expression of other genes. Gene masking is not a phenomenon in genetics. 

Example Question #3 : Help With Other Inheritance Patterns

Each of the listed statements about transposable genetic elements in eukaryotic genomes are true except for which one? 

Possible Answers:

Found in clusters within the genome

Activity is repressed by small RNAs that are transcribed by RNA polymerase II and III

Can introduce genetic mutations through creating inversions

Converted to RNA intermediate by transposase proteins 

Correct answer:

Converted to RNA intermediate by transposase proteins 

Explanation:

Transposable elements are divided into two categories: Type 1 (retrotransposons), which form RNA intermediates, and type 2 (transposons), which do not form RNA intermediates and directly enter a new site. Transposase proteins regulate the translocation of type 2 transposable elements, which do not require a RNA intermediate.

Example Question #4 : Help With Other Inheritance Patterns

Crossing foxes that are double heterozygotes for two genes regulating coat color yields 27 grey, 12 red and 9 black offspring. What mechanism explains the ratio of coat color observed in the offspring?

Possible Answers:

Mendelian inheritance

Epistasis

Pleiotropy 

X-chromosome linked

Chromosomal linkage

Correct answer:

Epistasis

Explanation:

If this were a Mendelian trait, we would expect a 9:3:3:1 ratio of offspring coat color. However, the results show a 9:4:3 ratio. Epistatic interaction between genes can be identified by one gene masking the phenotype of another gene. In this case, the double homozygote phenotype was masked by the red coat color phenotype (4 offspring, instead of seeing 3 red offspring). This suggests that the two coat color genes are epistatic.

Example Question #33 : Molecular Biology And Genetics

A student determines that color for a new diploid species is conferred by one gene. The student mates a homozygous dominant red mother with a homozygous recessive green father to yeild 100% of offspring that are both red and green. What form of inheritance best describes this? 

Possible Answers:

Polygenic trait

Epistasis

Incomplete dominance

Complete dominance

Codominance 

Correct answer:

Codominance 

Explanation:

The correct answer is codominance. According to this mode of inheritance, individuals that are heterozygous for a condition express both alleles equally. If the offspring were exhibited incomplete dominance, their phenotype would have been a red-green blend because the heterozygous condition is a blend of both alleles. Complete dominance occurs when the heterozygous condition exhibits the same phenotype as the homozygous dominant. In epistasis, the expression of one gene is dependent on the expression of a second, which is a form of inheritance that does not apply to this question. Finally, a polygenic trait is a trait that is conferred by multiple genes, a situation for which we know is not the case in this question. 

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

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