[11] Mastering Biology

Question 1

In a particular plant, leaf color is controlled by gene locus D. Plants with at least one D allele have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F1 offspring is allowed to self-pollinate. The predicted outcome of the F2 is diagrammed in the Punnett square shown in the figure above, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square. Which of the boxes marked 1−4 correspond(s) to plants with dark leaves?

Answer 1

1, 2, and 3

Question 2

In a particular plant, leaf color is controlled by gene locus D. Plants with at least one D allele have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F1 offspring is allowed to self-pollinate. The predicted outcome of the F2 is diagrammed in the Punnett square shown in the figure above, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square. Which of the boxes correspond(s) to plants with a heterozygous genotype?

Answer 2

2 and 3

Question 3

In a particular plant, leaf color is controlled by gene locus D. Plants with at least one D allele have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F1 offspring is allowed to self-pollinate. The predicted outcome of the F2 is diagrammed in the Punnett square shown in the figure above, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square. Which of the plants will be true-breeding?

Answer 3

1 and 4

Question 4

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

Answer 4

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

Question 5

Which of the following statements correctly describes a monohybrid cross?

a) A monohybrid cross involves organisms that are heterozygous for one character.
b) A monohybrid cross produces a single offspring.
c) A monohybrid cross involves a single parent.
d) A monohybrid cross is performed for one generation.

Answer 5

a) A monohybrid cross involves organisms that are heterozygous for one character.

Question 6

How many unique gametes could be produced through independent assortment by an individual with the genotype AaBbCCDdEE?

Answer 6

8

Question 7

Which of the following statements correctly describes one difference between the law of independent assortment and the law of segregation?

a) The law of segregation requires having two or more generations to describe.
b) The law of independent assortment explains the segregation of two or more genes relative to one another.
c) The law of segregation is accounted for by anaphase of mitosis.
d) The law of segregation explains the segregation of two or more genes relative to one another.

Answer 7

b) The law of independent assortment explains the segregation of two or more genes relative to one another.

Question 8

Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. What does this suggest about the trait?

Answer 8

that the parents were both heterozygous for a single trait

Question 9

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 9

HT

Question 10

When crossing an organism that is homozygous recessive for a single trait with one that is heterozygous for the same trait, what is the chance of producing an offspring with the homozygous recessive phenotype?

Answer 10

50%

Question 11

What was Mendel’s explanation for his observation that traits that had disappeared in the F1 generation reappeared in the F2 generation of the pea plants he used in his experiments?

Answer 11

Traits can be dominant or recessive, and the recessive traits were “hidden” by the dominant ones in the F1.

Question 12

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

Answer 12

One allele was dominant.

Question 13

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?

Answer 13

1/2

Question 14

In certain plants, the tall trait is dominant to the short trait. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

Answer 14

0

Question 15

Two true-breeding stocks of pea plants are crossed. One parent has red axial flowers, and the other has white terminal flowers; all F1 individuals have red axial flowers. The genes for flower color and location assort independently. If 1,000 F2 offspring resulted from the cross, approximately how many of them would you expect to have red terminal flowers?

Answer 15

190

Question 16

Two true-breeding stocks of pea plants are crossed. One parent has red axial flowers, and the other has white terminal flowers; all F1 individuals have red axial flowers. The genes for flower color and location assort independently. Among the F2 offspring, what is the probability of plants with white axial flowers?

Answer 16

3/16

Question 17

What is the difference between heterozygous and homozygous individuals?

Answer 17

All of the gametes from a homozygote carry the same version of the gene while those of a heterozygote will differ.

Question 18

When constructing a Punnett square, the symbols on the outside of the boxes represent _______, while those inside the boxes represent _______.

Answer 18

gametes, progeny

Question 19

True or false? The same phenotype can be produced by more than one genotype.

Answer 19

True

Question 20

True or false? In diploid organisms, a dominant phenotype will only be expressed if the individual is homozygous dominant for that trait.

Answer 20

False

Question 21

If an organism with the genotype AaBb produces gametes, what proportion of the gametes would be Bb?

Answer 21

None

Question 22

Two mice are heterozygous for albinism (Aa) . The dominant allele (A) codes for normal pigmentation, and the recessive allele (a) codes for no pigmentation. What percentage of their offspring would have an albino phenotype?

Answer 22

25%

Question 23

A tall, purple-flowered pea plant (TtPp) is allowed to self-pollinate. (The recessive alleles code for short plants and white flowers.) The phenotypic ratio of the resulting offspring is 9:3:3:1. What is the genotype of the plant whose phenotype appeared once out of every 16 offspring (the “1” in the 9:3:3:1 ratio)?

Answer 23

ttpp

Question 24

Which of the following statements apply to the variation in human skin color?

a) Variability in human skin color can be explained by the activity of a single gene.
b) The color of human skin and the skin of our closest primate relative exhibits a similar range in variability.
c) Human skin color variation likely evolved in response to differences in the intensity of sunlight around the world.
d) Human skin color variation is primarily determined by the type and amount of melanin pigment in the skin.
e) Human skin color variation evolved recently in hominid evolution, once some populations of our human ancestors migrated out of Africa.

Answer 24

c) Human skin color variation likely evolved in response to differences in the intensity of sunlight around the world.
d) Human skin color variation is primarily determined by the type and amount of melanin pigment in the skin.
e) Human skin color variation evolved recently in hominid evolution, once some populations of our human ancestors migrated out of Africa.

Question 25

Which of the following statements accurately describes melanin’s function?

a) Everyone has the same type of melanin, but the amount varies from person to person.
b) Melanin is a molecule that distinguishes humans from their primate relatives.
c) The more melanin an individual has in his or her skin cells, the more likely he or she is to get mutations in DNA.
d) Lighter skin has less of the dark-brown eumelanin that protects cells from UV damage.

Answer 25

d) Lighter skin has less of the dark-brown eumelanin that protects cells from UV damage.

Question 26

Darker skin is more prevalent in high-UV areas. Dr. Nina Jablonski proposed a hypothesis to explain the selective pressure for darker skin in these environments. On what evidence did she base this hypothesis?

Answer 26

the melanin in darkly pigmented skin protects circulating folate from being destroyed by UV radiation, and folate is important in human reproduction

Question 27

Human populations in low-UV environments tend to have more lightly pigmented skin. One explanation is that the selective pressure for dark skin decreases as UV intensity decreases. At the same time there is selection for lighter skin to absorb more UV radiation, which is needed for vitamin D production.

What evidence supports the vitamin D hypothesis for the evolution of lighter skin tones?

Answer 27

indigenous peoples living at high latitudes have darker skin, but they eat foods rich in vitamin D

Question 28

Based on the risk factors discussed in the video, which of the following groups would be most likely to develop the bone disease rickets?

Answer 28

children born to parents with dark skin living far from the equator

Question 29

In what way does natural selection depend on the specific environment in which an organism lives?

Answer 29

when the environment changes, traits that were beneficial to an organism may become harmful and vice versa.

Question 30

In humans, wavy hair occurs in heterozygotes (HSHC) offspring of people with straight hair (HSHS) and curly hair (HCHC). Which of the following crosses would produce offspring with the ratio of 1 straight:2 wavy:1 curly?

Answer 30

wavy x wavy

Question 31

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

Answer 31

pleiotropy

Question 32

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 expression of phenotypes?

Answer 32

pleiotropy

Question 33

Skin color in humans has a wide variety of phenotypes. The expression of this trait is caused by more than two genes. What type of inheritance pattern is responsible for this expression?

Answer 33

polygenic inheritance

Question 34

Characters in humans such as a person’s red and white blood cell counts vary quite a bit depending on such factors as altitude and physical activity. Traits like this are referred to as

Answer 34

multifactorial

Question 35

Which of the following statements correctly describes an example of epistasis?

a) Recessive genotypes for each of two genes (aabb) result in an albino corn snake.
b) In cacti, there are several genes for the type of spines.
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 a combination of multiple genes.

Answer 35

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

Question 36

Labrador retrievers are black, brown, or yellow. In a cross of a black female with a brown male, results can be all black puppies, 1/2 black to 1/2 brown puppies, or 3/4 black to 1/4 yellow puppies. These results indicate which of the following about the inheritance pattern of fur color in Labrador retrievers?

a) Yellow is dominant to black.
b) Brown is dominant to black.
c) Black is dominant to brown and to yellow.
d) Epistasis is involved.

Answer 36

Epistasis is involved.

Question 37

Labrador retrievers are black, brown, or yellow. In a cross of a black female with a brown male, results can be all black puppies, 1/2 black to 1/2 brown puppies, or 3/4 black to 1/4 yellow puppies. How many genes must be responsible for these coat colors in Labrador retrievers?

Answer 37

2

Question 38

Labrador retrievers have black, brown, or yellow fur. Fur color is controlled by two genes, one of which exhibits epistasis. Black (B) is dominant over brown (b) in one gene, and (E) is dominant over (e) in the other gene. The (E) gene is epistatic to the (B) gene. In a cross of a black female with a brown male, results can be all black puppies, 1/2 black to 1/2 brown puppies, or 3/4 black to 1/4 yellow puppies. In one cross of black × black, the results were as follows: 9/16 black, 4/16 yellow, 3/16 brown.

The genotype eebb must result in which of the following?

Answer 38

yellow

Question 39

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. True-breeding red-flowered long radishes are crossed with true-breeding white-flowered radishes. All of the F1 offspring are purple-flowered and long radishes. The flower color trait in radishes is an example of which of the following types of inheritance?

Answer 39

incomplete dominance

Question 40

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 40

epistasis

Question 41

The figure above shows a pedigree chart for a family, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle.

What is the genotype of individual II-5?

Answer 41

ww

Question 42

The figure above shows a pedigree chart for a family, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle.
What is the likelihood that the offspring of IV-3 and IV-4 will have the trait?

Answer 42

50%

Question 43

The figure above shows a pedigree chart for a family, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle.
What is the probability that individual III-1 is Ww?

Answer 43

1