Chapter 3

Question 1

Why was the pea plant an ideal plant for Mendel to use?

a. Generation time that is several years
b. Simple traits that are easy to identify
c. Low numbers of offspring produced
d. Expensive and time-consuming to grow
e. All of the above

Answer 1

b. Simple traits that are easy to identify

Question 2

Genes come in different versions called

a. alleles.
b. loci.
c. genotypes.
d. chromosomes.
genomes

Answer 2

a. alleles

Question 3

Which of the following statements is true?

a. The genotype is the physical appearance of a trait.
b. Alleles, genes, and loci are different names for the same thing.
c. The phenotype of a dominant allele is never seen in the F1 progeny of a monohybrid cross.
d. A testcross can be used to determine whether an individual is homozygous or heterozygous.
e. All of these statements are true.

Answer 3

d. A testcross can be used to determine whether an individual is homozygous or heterozygous.

Question 4

Gregor Mendel carried out a cross between two pea plants by taking pollen from a plant that was homozygous for round seeds and dusting the pollen onto the stigma of a plant homozygous for wrinkled seeds. Which of the following would be the reciprocal cross that Mendel had carried out for this experiment?

a. Homozygous round stigma pollinated with homozygous wrinkled
b. Homozygous round stigma pollinated with heterozygous wrinkled
c. Heterozygous round stigma pollinated with homozygous wrinkled
d. Homozygous wrinkled stigma pollinated with homozygous round
e. Homozygous wrinkled stigma pollinated with homozygous wrinkled

Answer 4

a. Homozygous round stigma pollinated with homozygous wrinkled

Question 5

Which of the following statements is true?

a. The probability of a woman giving birth to three girls in a row is 1/8.
b. The chi-square test is used to determine if observed outcomes are consistent with expected outcomes.
c. The probability of two or more independent events occurring together is calculated by multiplying their independent probabilities.
d. Branched diagrams are used for determining probabilities of various phenotypes or genotypes for genetic crosses involving more than one gene pair.
e. All of these statements are true.

Answer 5

e. All of these statements are true.

Question 6

In Labrador retrievers, black coat color is dominant to brown. Suppose that a black Lab is mated with a brown one and the offspring are 4 black puppies and 1 brown. What can you conclude about the genotype of the black parent?

a. The genotype must be BB.
b. The genotype must be bb.
c. The genotype must be Bb.
d. The genotype could be either BB or Bb.
e. The genotype cannot be determined from these data.

Answer 6

c. The genotype must be Bb.

Question 7

In Mendel’s peas, purple flower color is dominant to white. From which of the following descriptions can you not infer the genotype completely?

a. Purple
b. White
c. Pure-breeding purple
d. Heterozygous
e. More than one of the above

Answer 7

a. Purple

Question 8

Which of the following was not one of Mendel’s conclusions based on his monohybrid crosses?

a. Genes are carried on chromosomes.
b. Alleles exist in pairs.
c. Alleles segregate equally into gametes.
d. Alleles behave as particles during inheritance.
e. One allele can mask the expression of the other allele.

Answer 8

a. Genes are carried on chromosomes.

Question 9

In Mendel’s peas, yellow seeds are dominant to green. A pure-breeding yellow plant is crossed with a pure-breeding green plant. All of the offspring are yellow. If one of these yellow offspring is crossed with a green plant, what will be the expected proportion of plants with green seeds in the next generation?

a. 0%
b. 25%
c. 50%
d. 75%
e. 100%

Answer 9

c. 50%

Question 10

In a cross between pure-breeding tall plants with pure-breeding short plants, all of the F1 are tall. When these plants are allowed to fertilize themselves, the F2 plants occur in a ratio of 3 tall:1 short. Which of the following is not a valid conclusion from these results?

a. The allele that produces the tall condition is dominant to the allele that produces the short condition.
b. The difference between tall and short stature in these lines is controlled by a single gene pair.
c. During production of gametes in F1 plants, the tall and short alleles segregate from each other equally into the gametes.
d. The tall and short traits assort independently of each other in this cross.
e. Fertilization occurs randomly between gametes carrying the tall and short alleles.

Answer 10

d. The tall and short traits assort independently of each other in this cross.

Question 11

In poodles, black fur is dominant to white fur. A black poodle is crossed with a white poodle. In a litter of four, all of the puppies are black. What is the best conclusion?

a. The black poodle is definitely homozygous.
b. The black poodle is probably homozygous.
c. The black poodle is definitely heterozygous.
d. The black poodle is probably heterozygous.
e. The genotype of the black poodle cannot be inferred with this information.

Answer 11

b. The black poodle is probably homozygous.

Question 12

Honeybees have a haplo-diploid sex determination system where females develop from a fertilized egg (they are diploid, having one allele from the female queen and one allele from the male), and males develop from unfertilized eggs (they are haploid, having only one allele from the queen). Assuming that the queen is heterozygous for a particular gene, what is the probability that a female will inherit the recessive allele from her mother? What is the probability that a male will inherit a recessive allele from his mother?

a. The probability that a daughter will inherit a recessive allele from her mother is 50%; the probability that a son will inherit a recessive allele from his mother is 50%.
b. The probability that a daughter will inherit a recessive allele from her mother is 50%; the probability that a son will inherit a recessive allele from his mother is 100%.
c. The probability that a daughter will inherit a recessive allele from her mother is 100%; the probability that a son will inherit a recessive allele from his mother is 50%.
d. The probability that a daughter will inherit a recessive allele from her mother is 100%; the probability that a son will inherit a recessive allele from his mother is 100%.
e. The probability that a daughter will inherit a recessive allele from her mother is 0%; the probability that a son will inherit a recessive allele from his mother is 100%.

Answer 12

a. The probability that a daughter will inherit a recessive allele from her mother is 50%; the probability that a son will inherit a recessive allele from his mother is 50%.

Question 13

1. While doing field work in Madagascar, you discover a new dragonfly species that has either red (R) or clear (r) wings. Initial crosses indicate that R is dominant to r. You perform three crosses using three different sets of red-winged parents with unknown genotype and observe the following data:

Cross Phenotypes
1 72 red-winged, 24 clear-winged
2 12 red-winged
3 96 red-winged

Which cross is likely to have at least one parent with the genotype RR?

a. Cross 1
b. Cross 2
c. Cross 3
d. Crosses 1 and 2
e. Crosses 2 and 3

Answer 13

e. Crosses 2 and 3

Question 14

A couple has six daughters and is expecting a seventh child. What is the probability that this child will be a boy?

a. 1/2
b. 1/4
c. 1/16
d. 1/64
e. 1/128

Answer 14

a. 1/2

Question 15

If an organism of genotype Aa is used for a test cross, what is the genotype of the other individual used in the cross?

a. AA
b. Aa
c. Aa
d. The genotype cannot be known
e. Either a or b

Answer 15

c. Aa

Question 16

Which of the following crosses would produce a 1:1 ratio of phenotypes in the next generation?

a. AA AA
b. AA aa
c. Aa Aa
d. Aa aa
e. aa aa

Answer 16

d. Aa aa

Question 17

Which of the following crosses would produce a 3:1 ratio of phenotypes in the next generation?

a. AA AA
b. AA aa
c. Aa Aa
d. Aa aa
e. aa aa

Answer 17

c. Aa Aa

Question 18

Freckles are caused by a dominant allele. A man has freckles but one of his parents does not have freckles. What is his genotype?

a. Homozygous dominant
b. Homozygous recessive
c. Heterozygous
d. Heterologous
e. Homologous

Answer 18

c. Heterozygous

Question 19

Freckles are caused by a dominant allele. A man has freckles but one of his parents does not have freckles. The man has fathered a child with a woman that does not have freckles. What is the probability that their child has freckles?

a. 1/4
b. 1/3
c. 1/2
d. 2/3
e. 3/4

Answer 19

c. 1/2

Question 20

In animals, the inability to make the pigment melanin results in albinism, a recessive condition. Two unaffected parents, who have decided to have three children, have a first child that has albinism (genotype aa). What is the probability that the second and third children will also have albinism?

a. 1/4
b. 1/2
c. 1/16
d. 9/16
e. 1 (100%)

Answer 20

c. 1/16

Question 21

The ability to curl one’s tongue into a U-shape is a genetic trait. Curlers always have at least one curler parent but noncurlers can have one or both parents who are curlers. Using C and c to symbolize the alleles that control this trait, what is the genotype of a noncurler?

a. CC
b. Cc
c. cc
d. Any of the above could be correct.

Answer 21

c. cc

Question 22

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an AB gamete from an AaBb individual?

a. 1/4
b. 1/2
c. 1/16
d. 9/16
e. 1 (100%)

Answer 22

a. 1/4

Question 23

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an AB gamete from an AABb individual?

a. 1/4
b. 1/2
c. 1/16
d. 9/16
e. 1 (100%)

Answer 23

b. 1/2

Question 24

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an AABB zygote from a cross AaBb × AaBb?

a. 1/4
b. 1/2
c. 1/16
d. 9/16
e. 1 (100%)

Answer 24

c. 1/16

Question 25

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an AaBb zygote from a cross AaBb × AABB?

a. 1/4
b. 1/2
c. 1/16
d. 9/16
e. 1 (100%)

Answer 25

a. 1/4

Question 26

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an AB phenotype from a cross AaBb × AaBb?

a. 1/4
b. 1/2
c. 1/16
d. 9/16
e. 1 (100%)

Answer 26

d. 9/16

Question 27

Two gene loci, A and B, assort independently, and alleles A and B are dominant over alleles a and b. What is the probability of producing an AB phenotype from a cross aabb × AABB?

a. 1/4
b. 1/2
c. 1/16
d. 9/16
e. 1 (100%)

Answer 27

e. 1 (100%)

Question 28

In a cross between AaBbCc and AaBbcc, what proportion of the offspring would be expected to be A_bbcc? (A_ means AA or Aa.)

a. 3/256
b. 3/32
c. 3/16
d. 3/8
e. 3/4

Answer 28

b. 3/32

Question 29

In a cross between AABbCcDD and AaBbccdd, what proportion of the offspring would be expected to be A_B_C_D_? (A_ means AA or Aa.)

a. 3/256
b. 3/32
c. 3/16
d. 3/8
e. 3/4

Answer 29

d. 3/8

Question 30

In a cross between AaBbCcDdEe and AaBbccDdee, what proportion of the offspring would be expected to be A_bbC_ddE_? (A_ means AA or Aa.)

a. 3/256
b. 3/32
c. 3/16
d. 3/8
e. 3/4

Answer 30

a. 3/256

Question 31

Round seeds (R) is dominant to wrinkled seeds (r), and yellow seeds (Y) is dominant to green seeds (y). A true-breeding plant with round and yellow seeds is crossed to a true-breeding plant with wrinkled and green seeds. What is the genotype of the F1 progeny?

a. RRYY
b. RrYY
c. RRYy
d. RrYy
e. rryy

Answer 31

d. RrYy

Question 32

Round seeds (R) is dominant to wrinkled seeds (r), and yellow seeds (Y) is dominant to green seeds (y). A true-breeding pea plant with round and yellow seeds is crossed to a true-breeding plant with wrinkled and green seeds. The F1 progeny are allowed to self-fertilize. What is the probability of obtaining a round, yellow seed in the F2?

a. 3/4
b. 1/16
c. 9/16
d. 3/16
e. 1/2

Answer 32

c. 9/16

Question 33

Round seeds (R) is dominant to wrinkled seeds (r), and yellow seeds (Y) is dominant to green seeds (y). A true-breeding pea plant with round and yellow seeds is crossed to a true-breeding plant with wrinkled and green seeds. The F1 progeny are allowed to self-fertilize. What is the probability of obtaining a wrinkled, green seed in the F2?

a. 3/4
b. 1/16
c. 9/16
d. 3/16
e. 1/2

Answer 33

b. 1/16

Question 34

Round seeds (R) is dominant to wrinkled seeds (r), and yellow seeds (Y) is dominant to green seeds (y). A true-breeding pea plant with round and yellow seeds is crossed to a true-breeding plant with wrinkled and green seeds. The F1 progeny are allowed to self-fertilize. What is the probability of obtaining a yellow seed in the F2?

a. 3/4
b. 1/16
c. 9/16
d. 3/16
e. 1/2

Answer 34

a. 3/4

Question 35

Round seeds (R) is dominant to wrinkled seeds (r), and yellow seeds (Y) is dominant to green seeds (y). A plant of unknown genotype is testcrossed to a true-breeding plant with wrinkled and green seeds. The offspring produced were 53 round and yellow, 49 round and green, 44 wrinkled and yellow, 51 wrinkled and green. What is the likely genotype of the parent in question?

a. RRYY
b. RrYY
c. RRYy
d. RrYy
e. rryy

Answer 35

d. RrYy

Question 36

In dogs, black coat color (B) is dominant over brown (b), and solid coat color (S) is dominant over white spotted coat (s). A cross between a black, solid female and a black, solid male produces only puppies with black, solid coats. This same female was then mated with a brown, spotted male. Have of the offspring from this cross were black and solid, and half of the offspring were black and spotted. What is the genotype of the female?

a. BBSS
b. BbSS
c. BBSs
d. BbSs
e. bbss

Answer 36

c. BBSs

Question 37

In dogs, black coat color (B) is dominant over brown (b), and solid coat color (S) is dominant over white spotted coat (s). A cross between a black, solid female and a black, solid male produces only puppies with black, solid coats. This same female was then mated with a brown, spotted male. Have of the offspring from this cross were black and solid, and half of the offspring were black and spotted. Which of the following could be the genotype of the black, solid male?

a. BBSs
b. BBss
c. BbSS
d. BbSs
e. Bbss

Answer 37

c. BbSS

Question 38

In dogs, black coat color (B) is dominant over brown (b), and solid coat color (S) is dominant over white spotted coat (s). A cross between a black, solid female and a black, solid male produces only puppies with black, solid coats. This same female was then mated with a brown, spotted male. Have of the offspring from this cross were black and solid, and half of the offspring were black and spotted. What is the genotype of the brown, spotted male?

a. BBSS
b. BbSS
c. BBSs
d. BbSs
e. bbss

Answer 38

e. bbss

Question 39

A space capsule crashes to earth with an alien life form aboard. Two creatures emerge from the capsule, one with green skin and one with yellow skin. The yellow creature soon gives birth to offspring fathered by the green creature, producing 12 green and 8 yellow offspring. Green skin in these diploid creatures is dominant to yellow skin. You are curious to find out if the number of offspring significantly different from expected Mendelian ratios, so you perform a chi-square test. What is the chi-square value for this cross?

a. 0.2
b. 0.4
c. 0.8
d. 1.2
e. 1.6

Answer 39

c. 0.8

Question 40

A chi-square test was performed and indicated that the observed numbers of offspring were significantly different from the expected. Which of the following P-values would support this conclusion?

a. 0.995
b. 0.536
c. 0.024
d. 0.752
e. 0.159

Answer 40

c. 0.024

Question 41

How did Sutton’s chromosome theory of inheritance link Mendel’s work with a more mechanistic understanding of heredity?

Answer 41

Sutton documented the fact that each homologous pair of chromosomes consists of one maternal chromosome and one paternal chromosome. Showing that these pairs segregate independently into gametes in meiosis, he concluded that this process is the biological basis for Mendel’s principles of heredity.

Question 42

What conclusions did Mendel make from his monohybrid crosses?

Answer 42

Progeny inherit genetic factors from both parents.
Each individual possesses two factors (alleles) that control the appearance of each phenotypic trait.
The two alleles in each individual separate (segregate) during gametogenesis and are randomly distributed with equal probability of being distributed into the gametes.
From a cross between two true-breeding (homozygous) parents expressing different phenotypes for a given trait, traits that appeared unchanged in the F1 heterozygous offspring were dominant, and traits that disappeared in F1 heterozygous offspring were recessive.

Question 43

What is the difference between a backcross and a testcross?

Answer 43

A testcross is used to determine genotypes of individuals with a dominant phenotype that may be heterozygous or homozygous for a dominant allele. The unknown genotypes are revealed by crossing the dominant individual to a “tester” that is known to be homozygous for the recessive allele in question.

A backcross is the mating of F1 progeny back to one of their parents. A backcross can also be a testcross if the original parent is homozygous for the recessive allele. Backcrosses are typically used to introgress an allele of interest back into the genetic background of one of the original parents.