Genetics Practice Questions

Question 1

Which of the following is true about alleles?

A) They are identical versions of a gene.
B) They are different versions of a gene.
C) They always lead to dominant phenotypes.
D) They are only found in diploid organisms.

Answer 1

B) They are different versions of a gene.

Question 2

What is the phenotypic ratio of the F2 generation in a monohybrid cross?

A) 1:2:1
B) 3:1
C) 9:3:3:1
D) 1:1

Answer 2

B) 3:1

Question 3

The Law of Segregation states that:

A) Genes are linked together on the same chromosome.
B) Alleles for a gene separate during gamete formation.
C) Dominant alleles always mask recessive alleles.
D) Traits assort independently across generations.

Answer 3

B) Alleles for a gene separate during gamete formation.

Question 4

Which of the following represents incomplete dominance?

A) A red flower crossed with a white flower produces pink flowers.
B) Blood type AB in humans.
C) Green peas from yellow and green parents.
D) A mutation that results in complete loss of function.

Answer 4

A) A red flower crossed with a white flower produces pink flowers.

Question 5

What is a dihybrid cross?

A) A cross involving one gene with two alleles.
B) A cross between two heterozygous individuals for one trait.
C) A cross involving two genes, each with two alleles.
D) A cross involving linked genes.

Answer 5

C) A cross involving two genes, each with two alleles.

Question 6

In a test cross, an individual with a dominant phenotype is crossed with:

A) Another individual with the dominant phenotype.
B) A homozygous dominant individual.
C) A homozygous recessive individual.
D) A heterozygous individual.

Answer 6

C) A homozygous recessive individual.

Question 7

What phenotypic ratio is expected in a dihybrid cross for two independently assorting
traits in the F2 generation?

A) 9:3:3:1
B) 1:2:1
C) 3:1
D) 1:1

Answer 7

A) 9:3:3:1

Question 8

What is the expected genotypic ratio of offspring from a cross between two heterozygotes
(Yy x Yy)?

A) 1:1
B) 3:1
C) 1:2:1
D) 9:3:3:1

Answer 8

C) 1:2:1

Question 9

A heterozygous tall plant (Tt) is crossed with a homozygous recessive plant (tt). What is
the expected phenotypic ratio of the offspring?

A) 3:1
B) 1:2:1
C) 1:1
D) 9:3:3:1

Answer 9

C) 1:1

Question 10

If a yellow, smooth pea plant (YyRr) is self-crossed, what fraction of the offspring will
be green and wrinkled?

A) 1/16
B) 3/16
C) 9/16
D) 1/4

Answer 10

A) 1/16

Question 11

A yellow, smooth heterozygote (YyRr) is crossed with a green, wrinkled plant (yyrr).
What proportion of the offspring will be yellow and wrinkled?

A) 1/16
B) 3/16
C) 1/4
D) 1/2

Answer 11

C) 1/4

Question 12

Two pink snapdragons are crossed (Rr x Rr), where incomplete dominance governs
flower color. What is the expected phenotypic ratio (red:pink:white)?

A) 3:1:1
B) 1:1:1
C) 1:2:1
D) 9:3:3:1

Answer 12

C) 1:2:1

Question 13

What is the expected phenotypic ratio for a cross between two heterozygous individuals
in a monohybrid cross where one allele exhibits incomplete dominance?

A) 3:1
B) 9:3:3:1
C) 1:2:1
D) 1:1

Answer 13

C) 1:2:1

Question 14

A pea plant heterozygous for both seed color (Yy) and seed texture (Rr) is self-crossed.
How many offspring are expected to be green and smooth if 64 seeds are produced?

A) 12
B) 9
C) 16
D) 4

Answer 14

A) 12

Question 15

Which of the following best describes Mendel’s Law of Segregation?

a) Alleles for different traits assort independently during gamete formation.
b) Each gamete receives one allele for every gene, and the two alleles for a gene separate
during gamete formation.
c) Some alleles are dominant and mask the expression of recessive alleles.
d) Genes that are close together on the same chromosome assort independently.

Answer 15

b) Each gamete receives one allele for every gene, and the two alleles for a gene
separate during gamete formation.

Question 16

In a monohybrid cross between two heterozygous individuals (Tt × Tt), what is the expected
phenotypic ratio?

A) 1:1
B) 3:1
C) 9:3:3:1
D) 1:2:1

Answer 16

B) 3:1

Question 17

Which of the following scenarios would violate Mendel’s Law of Independent Assortment?

A) Genes for flower color and plant height are on different chromosomes.
B) A gene for flower color has two alleles, one dominant and one recessive.
C) Two genes are located close to each other on the same chromosome and tend to be
inherited together.
D) A plant is heterozygous for two traits.

Answer 17

C) Two genes are located close to each other on the same chromosome and tend
to be inherited together.

Question 18

You perform a test cross between a tall pea plant with an unknown genotype and a short pea
plant (tt). The offspring consist of 50% tall plants and 50% short plants. What was the genotype
of the tall parent?

A) TT
B) tt
C) Tt
D) TTT

Answer 18

C) Tt

Question 19

You are looking at two traits in peas: one for seed shape (R = round, r = wrinkled) and one
for seed color (Y = yellow, y = green). You have a plant with round yellow seeds, and you want
to know its genotype (it could be homozygous or heterozygous for each gene; i.e. R_Y_). To do
this you do a test cross: you cross your plant to a plant with wrinkled green seeds (rryy, which is
homozygous recessive for both genes). The offspring phenotypes are as follows:

25% round yellow
25% round green
25% wrinkled yellow
25% wrinkled green

What is the genotype of your round, yellow-seeded plant?

A) RrYy
B) RrYY
C) RRYY
D) RrYy or RRyy

Answer 19

A) RrYy