Question 1

Which of the following best describes the molecular basis for a dominant allele?

Accepted Answer

It encodes a functional protein, while the recessive allele often does not.

Question 2

A heterozygote for a gene with incomplete dominance will have which phenotype?

Accepted Answer

A phenotype intermediate between the two homozygotes.

Question 3

Which of the following is an example of codominance in humans?

Accepted Answer

ABO blood group, where both $$I^A$$ and $$I^B$$ alleles are expressed in AB individuals.

Question 4

In the inheritance of Tay-Sachs disease, why is the disease considered recessive at the organismal level but not at the molecular level?

Accepted Answer

Heterozygotes show no symptoms but produce half the normal enzyme activity.

Question 5

Which of the following best explains epistasis?

Accepted Answer

A gene at one locus affects the phenotypic expression of a gene at a second locus.

Question 6

A cross between two pink-flowered snapdragons (incomplete dominance, $$Rr) $$produces offspring in what phenotypic ratio?

Accepted Answer

$$1$$ red : $$2$$ pink : $$1$$ white

Question 7

Which of the following is NOT a correct statement about dominant alleles?

Accepted Answer

Dominant alleles are always the most common in the population.

Question 8

A Manx cat has a short tail due to a dominant allele (M). If two Manx cats are crossed, what is the expected ratio of Manx to non-Manx kittens?

Accepted Answer

$$2:1$$ Manx to non-Manx

Question 9

Which of the following best describes pleiotropy?

Accepted Answer

A single gene affects multiple traits.

Question 10

Which of the following is a real-life example of environmental effects on phenotype?

Accepted Answer

Siamese cats have darker fur on cooler parts of their bodies due to a temperature-sensitive enzyme.

Question 11

Which of the following best describes aneuploidy?

Accepted Answer

A condition where there is a gain or loss of a whole chromosome.

Question 12

What is the most common cause of aneuploidy in humans?

Accepted Answer

Nondisjunction during meiosis.

Question 13

If a gamete with $$n+1$$ chromosomes is fertilized by a normal gamete, what is the resulting zygote's chromosome number?

Accepted Answer

$$2n+1 ($$trisomic)

Question 14

Which chromosomal abnormality is associated with Down syndrome?

Accepted Answer

Trisomy 21

Question 15

Which of the following is NOT a structural chromosomal abnormality?

Accepted Answer

Aneuploidy

Question 16

A woman with genotype $$I^A i$$ and a man with genotype $$I^B i$$ have a child. What is the probability their child will have blood type O?

Accepted Answer

$$1/4$$

Question 17

Which of the following best explains why trisomies of chromosomes X, Y, and 21 are more likely to survive to adulthood than other trisomies?

Accepted Answer

These chromosomes have fewer genes or dosage compensation mechanisms.

Question 18

Which of the following is an example of a gene with multiple alleles in a population?

Accepted Answer

ABO blood group gene with $$I^A$$, $$I^B$$, and $$i$$ alleles.

Question 19

Which of the following is a possible outcome of nondisjunction during meiosis II?

Accepted Answer

Two normal gametes, one with $$n+1$$ chromosomes, and one with $$n-1$$ chromosomes.

Question 20

Which of the following best describes codominance?

Accepted Answer

Both alleles are fully expressed in the heterozygote.

Extensions to Mendelian Patterns of Inheritance and Chromosomal Aberrations

Study Guide - Practice Questions