GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Other Inheritance Patterns

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

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Example Questions

Example Question #1 : Help With Other Inheritance Patterns

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

III and IV

I and II

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:

incomplete dominance 

codominance

gene masking 

complete dominance

epistasis

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:

X-chromosome linked

Pleiotropy 

Chromosomal linkage

Epistasis

Mendelian inheritance

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 #5 : Help With Other Inheritance Patterns

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:

Codominance 

Polygenic trait

Epistasis

Incomplete dominance

Complete dominance

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. 

Example Question #6 : Help With Other Inheritance Patterns

Human beings are capable of having A, B, AB or O blood. While "A" and "B" alleles can be expressed at the same time on red blood cells, O type blood can only be a phenotype if a person has 2 "O" alleles.

Based on this information, what two modes of inheritance contribute to blood type in human beings?

Possible Answers:

Codominance and complete dominance

Complete dominance and incomplete dominance

Codominance and sex-linked dominance

Codominance and incomplete dominance

Correct answer:

Codominance and complete dominance

Explanation:

Since A and B can be expressed at the same time on a red blood cell, we can say that A and B are codominant to one another. On the other hand, this cannot be said for the O allele. If a person has an A allele and an O allele, that person will have type A blood. Both A and B are dominant over O. As a result, we also see complete dominance take place with blood types. To help solidify this concept, added below is a genotype/phentoype comparison:

A/A = A blood

A/O = A blood

O/O = O blood

B/B = B blood

B/O = B blood

A/B = AB blood

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