Question 1

Marfan syndrome is caused by a mutation in a single gene, FBN1, but results in multiple seemingly unrelated symptoms (skeletal, cardiovascular, and eye). What genetic concept does this illustrate?

Accepted Answer

Pleiotropy

Question 2

A dihybrid cross between two genes with no interaction (independent assortment) will produce which classic Mendelian phenotypic ratio in the F2 generation?

Accepted Answer

$$9:3:3:1$$

Question 3

In a pathway where two genes are required for pigment production in cats, a cross between $$Ww$$ and $$Cc$$ cats produces some white cats. What is the most likely explanation for the white phenotype in this scenario?

Accepted Answer

Epistasis, where a mutation in either gene blocks pigment production

Question 4

Which type of gene interaction results in a 13:3 phenotypic ratio in a dihybrid cross?

Accepted Answer

Dominant suppression epistasis

Question 5

A complementation test is performed by crossing two true-breeding mutants with the same phenotype. If the F1 offspring have the wild-type phenotype, what does this indicate?

Accepted Answer

The mutations are in different genes

Question 6

In the Mexican cave tetra, blindness is inherited as a recessive trait. If two blind fish from different caves are crossed and their offspring can see, what does this suggest about the genetic basis of blindness in these fish?

Accepted Answer

Blindness in the two fish is caused by mutations in different genes

Question 7

Which of the following best describes the 'one gene-one enzyme' hypothesis proposed by Beadle and Tatum?

Accepted Answer

Each gene encodes a single enzyme that affects a specific step in a metabolic pathway

Question 8

A dihybrid cross of $$PpRr$$ bean plants, where either dominant allele ($$P or$$ $$R) is $$sufficient for purple color, will result in which phenotypic ratio for purple to white flowers?

Accepted Answer

$$15:1$$

Question 9

In a biosynthetic pathway, a mutation in gene A prevents the conversion of precursor 1 to precursor 2, while a mutation in gene B prevents the conversion of precursor 2 to pigment. What is the expected outcome if both mutations are present in an organism?

Accepted Answer

No pigment is produced

Question 10

Which of the following is NOT a requirement for a complementation analysis to distinguish between mutations in the same or different genes?

Accepted Answer

Mutations must be dominant

Question 11

A cross between two white-flowered sweet pea plants (one $$ccPP$$, one $$CCpp) $$produces all purple-flowered offspring. What does this result indicate?

Accepted Answer

The mutations are in different genes

Question 12

Which of the following best describes epistasis?

Accepted Answer

An allele of one gene modifies or prevents the expression of alleles of another gene

Question 13

In a metabolic pathway for phenylalanine breakdown, a mutation in the gene encoding phenylalanine hydroxylase leads to phenylketonuria (PKU). What is the consequence of this mutation?

Accepted Answer

Phenylalanine accumulates and becomes toxic to neurons

Question 14

Which of the following is an example of complementary gene interaction?

Accepted Answer

Both dominant alleles are required for the dominant phenotype

Question 15

If a dihybrid cross produces a $$9:7$$ ratio of phenotypes, which type of gene interaction is most likely occurring?

Accepted Answer

Complementary gene interaction

Question 16

A geneticist crosses two strains of Mexican cavefish, both blind due to autosomal recessive mutations. The F1 offspring are all blind. What does this suggest?

Accepted Answer

The mutations are in the same gene (non-complementation)

Question 17

Which of the following is a real-world example of pleiotropy?

Accepted Answer

A mutation in FBN1 causing Marfan syndrome with multiple symptoms

Question 18

In a dihybrid cross involving dominant suppression epistasis, what is the expected ratio of suppressed to unsuppressed phenotypes?

Accepted Answer

$$13:3$$

Question 19

Which of the following statements about complementation groups is correct?

Accepted Answer

A complementation group refers to a set of mutations in the same gene

Question 20

Which of the following is NOT a type of gene interaction that alters Mendelian ratios?

Accepted Answer

No interaction (independent assortment)

Epistasis and Complementation: Gene Interactions in Genetics

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