What do we mean when we use the terms monohybrid cross and dihybrid cross?
A) A monohybrid cross involves a single parent, whereas a dihybrid cross involves two parents.
B) A monohybrid cross produces a single progeny, whereas a dihybrid cross produces two
progeny.
C) A dihybrid cross involves organisms that are heterozygous for two characters, and a
monohybrid cross involves only one.
D) A monohybrid cross is performed for one generation, whereas a dihybrid cross is performed
for two generations.
E) A monohybrid cross results in a 9:3:3:1 ratio, whereas a dihybrid cross gives a 3:1 ratio.

A dihybrid cross involves organisms that are heterozygous for two characters, and a
monohybrid cross involves only one.

What was the most significant conclusion that Gregor Mendel drew from his experiments with
pea plants?
A) There is considerable genetic variation in garden peas.
B) Traits are inherited in discrete units, and are not the results of "blending"
C) Recessive genes occur more frequently in the F1 generation than do dominant ones.
D) Genes are composed of DNA.
E) An organism that is homozygous for many recessive traits is at a disadvantage.

Traits are inherited in discrete units, and are not the results of "blending"

How many unique gametes could be produced through independent assortment by an
individual with the genotype AaBbCCDdEE?
A) 4
B) 8
C) 16
D) 32
E) 64

8

The individual with genotype AaBbCCDdEE can make many kinds of gametes. Which of the
following is the major reason?
A) segregation of maternal and paternal alleles
B) recurrent mutations forming new alleles
C) crossing over during prophase I
D) different possible assortment of chromosomes into gametes
E) the tendency for dominant alleles to segregate together

different possible assortment of chromosomes into gametes

Why did Mendel continue some of his experiments to the F2 or F3 generation?
A) to obtain a larger number of offspring on which to base statistics
B) to observe whether or not a recessive trait would reappear
C) to observe whether or not the dominant trait would reappear
D) to distinguish which alleles were segregating
E) to be able to describe the frequency of recombination

to observe whether or not a recessive trait would reappear

Which of the following differentiates between independent assortment and segregation?
A) The law of independent assortment requires describing two or more genes relative to one
another.
B) The law of segregation requires describing two or more genes relative to one another.
C) The law of segregation requires having two or more generations to describe.
D) The law of independent assortment is accounted for by observations of prophase I.
E) The law of segregation is accounted for by anaphase of mitosis.

The law of independent assortment requires describing two or more genes relative to one
another.

Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. What does
this suggest?
A) that the parents were true-breeding for contrasting traits
B) that the trait shows incomplete dominance
C) that a blending of traits has occurred
D) that the parents were both heterozygous for a single trait
E) that each offspring has the same alleles for each of two traitsanother.

that the parents were both heterozygous for a single trait

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for
tail length (T). Its genotype is HhTt. Which of the following genotypes is possible in a gamete
from this organism?
A) tt
B) Hh
C) HhTt
D) T
E) HT

HT

When crossing an organism that is homozygous recessive for a single trait with a
heterozygote, what is the chance of producing an offspring with the homozygous recessive
phenotype?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%

50%

Mendel accounted for the observation that traits that had disappeared in the F1 generation
reappeared in the F2 generation by proposing that
A) new mutations were frequently generated in the F2 progeny, "reinventing" traits that had been
lost in the F1.
B) the mechanism controlling the appearance of traits was different between the F1 and the F2
plants.
C) traits can be dominant or recessive, and the recessive traits were obscured by the dominant
ones in the F1.
D) the traits were lost in the F1 due to dominance of the parental traits.
E) members of the F1 generation had only one allele for each trait, but members of the F2 had
two alleles for each trait.

traits can be dominant or recessive, and the recessive traits were obscured by the dominant
ones in the F1.

Which of the following calculations require that you utilize the addition rule?
A) Calculate the probability of black offspring from the cross AaBb × AaBb, when B is the
symbol for black.
B) Calculate the probability of children with both cystic fibrosis and polydactyly when parents
are each heterozygous for both genes.
C) Calculate the probability of each of four children having cystic fibrosis if the parents are both
heterozygous.
D) Calculate the probability of a child having either sickle-cell anemia or cystic fibrosis if
parents are each heterozygous for both.
E) Calculate the probability of purple flower color in a plot of 50 plants seeded from a self-
fertilizing heterozygous parent plant.

Calculate the probability of a child having either sickle-cell anemia or cystic fibrosis if
parents are each heterozygous for both.

Which of the following is the best statement of the use of the addition rule of probability?
A) the probability that two or more independent events will both occur
B) the probability that two or more independent events will both occur in the offspring of one set
of parents
C) the probability that either one of two independent events will occur
D) the probability of producing two or more heterozygous offspring
E) the likelihood that a trait is due to two or more meiotic events

the probability that either one of two independent events will occur

Given the parents AABBCc × AabbCc, assume simple dominance for each trait and
independent assortment. What proportion of the progeny will be expected to phenotypically
resemble the first parent?
A) 1/4
B) 1/8
C) 3/4
D) 3/8
E) 1

3/4

In the cross AaBbCc × AaBbCc, what is the probability of producing the genotype AABBCC?
A) 1/4
B) 1/8
C) 1/16
D) 1/32
E) 1/64

1/64

In certain plants, tall is dominant to short. If a heterozygous plant is crossed with a
homozygous tall plant, what is the probability that the offspring will be short?
A) 1
B) 1/2
C) 1/4
D) 1/6
E) 0

0

Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails
(t). What fraction of the progeny of crosses BbTt × BBtt will be expected to have black fur and
long tails?
A) 1/16
B) 3/16
C) 3/8
D) 1/2
E) 9/16

1/2

Why did the F1 offspring of Mendel's classic pea cross always look like one of the two
parental varieties?
A) No genes interacted to produce the parental phenotype.
B) Each allele affected phenotypic expression.
C) The traits blended together during fertilization.
D) One allele was dominant.
E) Phenotype was not dependent on genotype.

One allele was dominant.

Mendel's second law of independent assortment has its basis in which of the following events
of meiosis I?
A) synapsis of homologous chromosomes
B) crossing over
C) alignment of tetrads at the equator
D) separation of homologs at anaphase
E) separation of cells at telophase

alignment of tetrads at the equator

Mendel's observation of the segregation of alleles in gamete formation has its basis in which
of the following phases of cell division?
A) prophase I of meiosis
B) anaphase II of meiosis
C) metaphase I of meiosis
D) anaphase I of meiosis
E) anaphase of mitosis

anaphase I of meiosis

The fact that all seven of the pea plant traits studied by Mendel obeyed the principle of
independent assortment most probably indicates which of the following?
A) None of the traits obeyed the law of segregation.
B) The diploid number of chromosomes in the pea plants was 7.
C) All of the genes controlling the traits were located on the same chromosome.
D) All of the genes controlling the traits behaved as if they were on different chromosomes.
E) The formation of gametes in plants occurs by mitosis only.

All of the genes controlling the traits behaved as if they were on different chromosomes.

Marfan syndrome in humans is caused by an abnormality of the connective tissue protein
fibrillin. Patients are usually very tall and thin, with long spindly fingers, curvature of the spine,
sometimes weakened arterial walls, and sometimes ocular problems, such as lens dislocation.
Which of the following would you conclude about Marfan syndrome from this information?
A) It is recessive.
B) It is dominant.
C) It has a late age of onset (> 60).
D) It is pleiotropic.
E) It is epistatic.

It is pleiotropic.

22) In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous (Rr)
offspring of red (RR) and white (rr) homozygotes. Which of the following crosses would
produce offspring in the ratio of 1 red:2 roan:1 white?
A) red × white
B) roan × roan
C) white × roan
D) red × roan
E) The answer cannot be determined from the information provided.

roan × roan

Which of the following describes the ability of a single gene to have multiple phenotypic
effects?
A) incomplete dominance
B) multiple alleles
C) pleiotropy
D) epistasis

pleiotropy

Cystic fibrosis affects the lungs, the pancreas, the digestive system, and other organs,
resulting in symptoms ranging from breathing difficulties to recurrent infections. Which of the
following terms best describes this?
A) incomplete dominance
B) multiple alleles
C) pleiotropy
D) epistasis
E) codominance

pleiotropy

Which of the following is an example of polygenic inheritance?
A) pink flowers in snapdragons
B) the ABO blood group in humans
C) Huntington's disease in humans
D) white and purple flower color in peas
E) skin pigmentation in humans

skin pigmentation in humans

Hydrangea plants of the same genotype are planted in a large flower garden. Some of the
plants produce blue flowers and others pink flowers. This can be best explained by which of the
following?
A) the knowledge that multiple alleles are involved
B) the allele for blue hydrangea being completely dominant
C) the alleles being codominant
D) the fact that a mutation has occurred
E) environmental factors such as soil pH

environmental factors such as soil pH

Which of the following provides an example of epistasis?
A) Recessive genotypes for each of two genes (aabb) result in an albino corn snake.
B) The allele b17 produces a dominant phenotype, although b1 through b16 do not.
C) In rabbits and many other mammals, one genotype (ee) prevents any fur color from
developing.
D) In Drosophila (fruit flies), white eyes can be due to an X-linked gene or to a combination of
other genes.
E) In cacti, there are several genes for the type of spines.

In rabbits and many other mammals, one genotype (ee) prevents any fur color from
developing.

A scientist discovers a DNA-based test for one allele of a particular gene. This and only this
allele, if homozygous, produces an effect that results in death at or about the time of birth. Of the
following, which is the best use of this discovery?
A) Screen all newborns of an at-risk population.
B) Design a test for identifying heterozygous carriers of the allele.
C) Introduce a normal allele into deficient newborns.
D) Follow the segregation of the allele during meiosis.
E) Test school-age children for the disorder.

Design a test for identifying heterozygous carriers of the allele.

The frequency of heterozygosity for the sickle-cell anemia allele is unusually high,
presumably because this reduces the frequency of malaria. Such a relationship is related to which
of the following?
A) Mendel's law of independent assortment
B) Mendel's law of segregation
C) Darwin's explanation of natural selection
D) Darwin's observations of competition
E) the malarial parasite changing the allele

Darwin's explanation of natural selection

One of two major forms of a human condition called neurofibromatosis (NF 1) is inherited as
a dominant gene, although it may range from mildly to very severely expressed. If a young child
is the first in her family to be diagnosed, which of the following is the best explanation?
A) The mother carries the gene but does not express it at all.
B) One of the parents has very mild expression of the gene.
C) The condition skipped a generation in the family.
D) The child has a different allele of the gene than the parents.
Answer: B
Topic: Concept 11.4
Skill: Synthesis/Evaluation
Learning Outcome: 11.4

One of the parents has very mild expression of the gene.