Question 1

Which of the following best explains why the blending hypothesis of inheritance was rejected in favor of Mendel’s particulate theory of inheritance?

Accepted Answer

Blending inheritance could not explain the reappearance of traits after several generations.

Question 2

A true-breeding pea plant with purple flowers (PP) is crossed with a true-breeding plant with white flowers (pp). What is the expected genotype and phenotype ratio in the F2 generation after self-fertilization of the F1 hybrids?

Accepted Answer

Genotype ratio 1 PP : 2 Pp : 1 pp; Phenotype ratio 3 purple : 1 white

Question 3

Which of the following statements about Mendel’s law of segregation is correct?

Accepted Answer

Allele pairs separate during the production of gametes, so each gamete carries only one allele for each gene.

Question 4

In a dihybrid cross between two heterozygous pea plants (RrYy × RrYy), what is the expected phenotypic ratio of the offspring according to Mendel’s law of independent assortment?

Accepted Answer

$$9:3:3:1$$

Question 5

A black Labrador retriever (B_N_) is crossed with a chocolate Labrador (bbN_). If the black Labrador is heterozygous for both genes, what proportion of the offspring will be chocolate and blind (bbnn)?

Accepted Answer

$$\frac{1}{16}$$

Question 6

A woman with genotype Hh for widow’s peak (H = widow’s peak, h = straight hairline) and a man with genotype hh have a child. What is the probability that their child will have a widow’s peak?

Accepted Answer

$$\frac{1}{2}$$

Question 7

Which of the following is an example of incomplete dominance in humans?

Accepted Answer

Hypercholesterolemia, where heterozygotes have a phenotype intermediate between normal and affected individuals.

Question 8

Which genetic phenomenon explains why a single gene mutation can cause multiple symptoms in different organs, as seen in sickle-cell disease?

Accepted Answer

Pleiotropy

Question 9

Human skin color is determined by the additive effects of several genes. What type of inheritance does this illustrate?

Accepted Answer

Polygenic inheritance

Question 10

Which of the following best describes the chromosomal basis of Mendel’s law of independent assortment?

Accepted Answer

Homologous chromosome pairs orient independently at metaphase I of meiosis.

Question 11

Linked genes are inherited together because they are:

Accepted Answer

Located close together on the same chromosome.

Question 12

A recombination frequency of 11% between two genes means:

Accepted Answer

11% of the offspring are recombinants, and the genes are relatively close on the chromosome.

Question 13

In humans, which parent determines the sex of the offspring, and why?

Accepted Answer

The father, because he can contribute either an X or a Y chromosome.

Question 14

Why are X-linked recessive disorders more common in males than in females?

Accepted Answer

Males have only one X chromosome, so a single recessive allele will cause the disorder.

Question 15

A woman who is a carrier for hemophilia (an X-linked recessive disorder) marries a normal man. What is the probability that their son will have hemophilia?

Accepted Answer

$$\frac{1}{2}$$

Question 16

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

Accepted Answer

AB blood type, where both A and B antigens are expressed on red blood cells.

Question 17

Carrier screening and fetal testing can provide important genetic information. Which of the following is a disadvantage of amniocentesis compared to chorionic villus sampling (CVS)?

Accepted Answer

Results from amniocentesis take several weeks, while CVS results are available in a few days.

Question 18

Which of the following best explains why the sickle-cell allele persists in some human populations?

Accepted Answer

Heterozygotes have increased resistance to malaria.

Question 19

Which of the following is NOT a polygenic trait?

Accepted Answer

Widow’s peak

Question 20

A geneticist finds that two genes have a recombination frequency of 9%. What does this indicate about their physical relationship on a chromosome?

Accepted Answer

They are relatively close together on the same chromosome.

Patterns of Inheritance: Mendelian and Non-Mendelian Genetics

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