All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources
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?
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?
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
Bb = 0.44
bb = 0.11
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 #2 : Help With Hardy Weinberg
Which of the following is not an assumption of the Hardy-Weinberg equilibrium?
No genetic drift within a population
No natural selection within a population
Non-random mating within a population
No gene flow between populations
No mutations within a population
Non-random mating within a population
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 : Help With Hardy Weinberg
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?
Homozygous dominant: 0.20
Heterozygous: 0.50
Homozygous recessive: 0.30
Homozygous dominant: 0.30
Heterozygous: 0.50
Homozygous recessive: 0.20
Homozygous dominant: 0.25
Heterozygous: 0.50
Homozygous recessive: 0.25
Homozygous dominant: 0.30
Heterozygous: 0.20
Homozygous recessive: 0.50
Homozygous dominant: 0.50
Heterozygous: 0.30
Homozygous recessive: 0.20
Homozygous dominant: 0.30
Heterozygous: 0.50
Homozygous recessive: 0.20
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 #12 : Help With Hardy Weinberg
Which of the following is not a tenet of Hardy-Weinberg equilibrium?
Large population
Randomized mating
Genetic drift
No natural selection
No migration
Genetic drift
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 #31 : 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
IV only
I, II, and III
I and II
III and IV
I and II
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 #21 : Inheritance
When the expression and subsequent phenotype of one gene is dependent on the expression of another gene, this type of phenonemon is known as __________.
epistasis
incomplete dominance
codominance
gene masking
complete dominance
epistasis
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 #22 : Inheritance
Each of the listed statements about transposable genetic elements in eukaryotic genomes are true except for which one?
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
Found in clusters within the genome
Converted to RNA intermediate by transposase proteins
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 #23 : Inheritance
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?
Pleiotropy
Chromosomal linkage
Mendelian inheritance
Epistasis
X-chromosome linked
Epistasis
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 #24 : Inheritance
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?
Epistasis
Complete dominance
Codominance
Polygenic trait
Incomplete dominance
Codominance
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
