chapter 14 mendelian genetics

Question 1

What do we mean when we use the terms monohybrid cross and dihybrid cross?

Answer 1

B) A dihybrid cross involves organisms that are heterozygous for two characters that are being studied, and a monohybrid cross involves organisms that are heterozygous for only one character being studied.

Question 2

What was the most significant conclusion that Gregor Mendel drew from his experiments with pea plants?

Answer 2

B) Traits are inherited in discrete units and are not the results of “blending.”

Question 3

The individual with genotype AaBbCCDdEE can make many kinds of gametes. Which of the following is the major reason?

Answer 3

C) different possible assortment of chromosomes into gametes

Question 4

Mendel continued some of his experiments into the F2 or F3 generation to ________.

Answer 4

B) observe whether or not a recessive trait would reappear

Question 5

Which of the following statements about independent assortment and segregation is correct?

Answer 5

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

Question 6

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?

Answer 6

D) HT

Question 7

Mendel accounted for the observation that traits that had disappeared in the F1 generation reappeared in the F2 generation by proposing that ________.

Answer 7

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

Question 8

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?

Answer 8

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

Question 9

Mendel’s second law of independent assortment has its basis in which of the following events of meiosis I?
A) synapsis of homologous chromosomes

Answer 9

C) alignment of tetrads at the equator

Question 10

Skin colour in a certain species of fish is inherited via a single gene with four different alleles. How many different types of gametes would be possible in this system?

Answer 10

B) 4

Question 11

Why did the F1 offspring of Mendel’s classic pea cross always look like one of the two parental varieties?

Answer 11

D) One allele was dominant.

Question 12

Mendel crossed yellow-seeded and green-seeded pea plants and then allowed the offspring to self-pollinate to produce an F2 generation. The results were as follows: 6,022 yellow and 2,001 green (8,023 total). The allele for green seeds has what relationship to the allele for yellow seeds?

Answer 12

C) recessive

Question 13

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation, but both have one parent who is albino (without melanin pigmentation). What is the probability that their first child will be an albino?

Answer 13

C) 1/4

Question 14

Albinism is an autosomal (not sex-linked) recessive trait. A man and woman are both of normal pigmentation and have one child out of three who is albino (without melanin pigmentation). What are the genotypes of the albino’s parents?

Answer 14

C) Both parents must be heterozygous.

Question 15

A black guinea pig crossed with an albino guinea pig produced twelve black offspring. When the albino was crossed with a second black animal, six blacks and six albinos were obtained. What is the best explanation for this genetic situation?

Answer 15

A) Albino is recessive; black is dominant.

Question 16

Gray seed colour in peas is dominant to white. Assume that Mendel conducted a series of experiments where plants with gray seeds were crossed among themselves, and the following progeny were produced: 302 gray and 98 white.

(a) What is the most probable genotype of each parent?
(b) Based on your answer in (a) above, what genotypic and phenotypic ratios are expected in these progeny? (Assume the following symbols: G = gray and g = white.)

Answer 16

B) (a) Gg × Gg; (b) genotypic = 1:2:1, phenotypic = 3:1

Question 17

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?

Answer 17

D) 0

Question 18

In the cross AaBbCc × AaBbCc, what is the probability of producing the genotype AABBCC?

Answer 18

D) 1/64

Question 19

A man has extra digits (six fingers on each hand and six toes on each foot). His wife and their daughter have a normal number of digits. Having extra digits is a dominant trait. The couple’s second child has extra digits. What is the probability that their next (third) child will have extra digits?

Answer 19

A) 1/2

Question 20

Suppose two AaBbCc individuals are mated. Assuming that the genes are not linked, what fraction of the offspring are expected to be homozygous recessive for the three traits?

Answer 20

D) 1/64

Question 21

In cattle, roan coat colour (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?

Answer 21

B) roan × roan

Question 22

Which of the following describes the ability of a single allele to have multiple phenotypic effects?

Answer 22

C) pleiotropy

Question 23

Which of the following is an example of polygenic inheritance?

Answer 23

D) skin pigmentation in humans

Question 24

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?

Answer 24

D) environmental factors such as soil pH

Question 25

Which of the following provides an example of epistasis?

Answer 25

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

Question 26

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant trait. If true-breeding red long radishes are crossed with true-breeding white oval radishes, the F1 will be expected to be which of the following?

Answer 26

C) purple and long

Question 27

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The flower colour trait in radishes is an example of which of the following?

Answer 27

D) incomplete dominance

Question 28

Skin colour in a certain species of fish is inherited via a single gene with four different alleles. One fish of this type has alleles 1 and 3 (S1S3) and its mate has alleles 2 and 4 (S2S4). If each allele confers a unit of colour darkness such that S1 has one unit, S2 has two units, and so on, then what proportion of their offspring would be expected to have five units of colour?

Answer 28

C) 1/2

Question 29

Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cactuses have dull spines. At the same time, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. The relationship between genes S and N is an example of ________.

Answer 29

B) epistasis

Question 30

Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cactuses have dull spines. At the same time, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. A cross between a true-breeding sharp-spined cactus and a spineless cactus would produce ________.

Answer 30

A) all sharp-spined progeny

Question 31

An obstetrician knows that one of her patients is a pregnant woman whose foetus is at risk for a serious disorder that is detectable biochemically in foetal cells. The obstetrician would most reasonably offer which of the following procedures to her patient?

Answer 31

C) amniocentesis or CVS

Question 32

In some parts of Africa, 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?

Answer 32

C) Darwin’s explanation of natural selection

Question 33

Which of the following statements is a correct explanation for the observation that all offspring exhibit a phenotype for a particular trait that appears to be a blend of the two parental varieties?

Answer 33

A) Neither of the parental genes is dominate over the other.