Chapter 14 Questions

Question 1

Which choice below is a basic difference between Mendel’s particulate hypothesis and the hypothesis of blending inheritance?

Answer 1

The blending inheritance hypothesis, but not the particulate hypothesis, maintained that after a mating, the genetic material provided by each of the two parents is mixed in the offspring, losing its individual identity.

Question 2

If a plant variety is true-breeding for a dominant trait, then _____.

Answer 2

if the plant were allowed to self-pollinate, all of the progeny would have the dominant trait

-All the progeny would show the same phenotype.

Question 3

A = big apples; R = red apples; a = small apples; r = yellow apples. You have one tree that produces big yellow apples and another tree that produces small red apples. When the two are crossed, you find that half of the new trees produce big red apples and half produce big yellow apples. What are the genotypes of the parents?

Answer 3

AArr and aaRr

-Trees that produce big yellow apples could be AArr or Aarr. Trees that produce small red apples could be aaRR or aaRr. Because all the offspring are big, the big parent must be homozygous for A. Because half the apples are red and half are yellow, the red parent must be heterozygous for red. The conclusion is that the cross must be AArr x aaRr.

Question 4

Assume tall (T) is completely dominant to dwarf (t) in a certain species of plant. If a homozygous dominant individual is crossed with a homozygous dwarf, the offspring will _____.

Answer 4

all be tall

-The tall allele is completely dominant to the dwarf allele.

Question 5

The F1 generation differed from the F2 in Mendel’s experiments in that _____.

Answer 5

all of the F1 showed the dominant phenotype, but only three-fourths of the F2 did

Question 6

Physically, what are different alleles?

Answer 6

Different alleles are different DNA sequences found at the same locus on homologous chromosomes.

-Unless a mutation has occurred during DNA synthesis, sister chromatids will always carry the same allele.

Question 7

In a certain plant, the alleles A, B, and C are completely dominant to the alleles a, b, and c. A plant with the genotype AABbcc will have the same phenotype as a plant with the genotype _____.

Answer 7

AaBBcc

Question 8

Pea plants are tall if they have the genotype TT or Tt, and they are short if they have genotype tt. A tall plant is mated with a short plant. Which outcome below would indicate that the tall parent plant was heterozygous?

Answer 8

The ratio of tall offspring to short offspring is 1:1.

-If one parent has the genotype Tt and the other parent has the genotype tt, about half of the offspring will be tall.

Question 9

What is indicated when a single-character testcross yields offspring that all have the dominant phenotype?

Answer 9

The parent with the dominant phenotype was homozygous.

-If all the progeny show the dominant phenotype, the parent must have been homozygous, transmitting the dominant allele to all of the offspring.

Question 10

If an organism that is homozygous dominant is crossed with a heterozygote for that trait, the offspring will be _____.

Answer 10

all of the dominant phenotype

-The offspring of an AA x Aa cross are either AA or Aa. All will express the dominant phenotype.

Question 11

In Mendel’s monohybrid cross of purple-flowered and white-flowered peas, all members of the F1 generation had the _____ phenotype because their genotype was _____ at the flower-color locus.

Answer 11

purple-flowered … heterozygous

Question 12

If the two traits that Mendel looked at in his dihybrid cross of smooth yellow peas with wrinkled green peas had been controlled by genes that were located near each other on the same chromosome, then the F2 generation _____.

Answer 12

would have deviated from the 9:3:3:1 phenotypic ratio that is predicted by the law of independent assortment

Question 13

In carrying out his breeding studies, Mendel examined characters that had which of the following properties?

Answer 13

• They were controlled by loci that were (or behaved as if they were) on different chromosomes.
• It was possible to isolate true-breeding varieties for each trait.
• The traits varied in an either-or fashion.
• The characters each were controlled by a single gene.

Question 14

The law of independent assortment _____.

Answer 14

• states that the alleles at different loci segregate independently from one another during a dihybrid cross
• can account for a 9:3:3:1 ratio seen in the F2 generation
• applies only to genes that are present on different chromosomes (or behave as if they were)

Question 15

Homologous pairs of chromosomes often _____.

Answer 15

contain different alleles

-Pairs of homologous chromosomes carry the same genes.

Question 16

If each parent can produce 100 genetically distinct gametes, how many genetically distinct offspring can two parents produce?

Answer 16

10,000

-100 × 100 = 10,000. The rule of multiplication applies to these independent events.

Question 17

Pea flowers may be purple (P) or white (p). Pea seeds may be round (R) or wrinkled (r). What proportion of the offspring from the cross PpRr x PpRr will have white flowers and wrinkled seeds?

Answer 17

1/16

Question 18

An AABbccDdEeFF individual is crossed with an individual with the genotype AaBBCCDdEeff. What is the probability that their offspring will have the genotype AaBBCcddEEFf?

Answer 18

1/64

Question 19

If a heterozygous plant is allowed to self-pollinate, what proportion of the offspring will also be heterozygous?

Answer 19

1/2

Question 20

An individual with the genotype AABbCcDD can make how many different kinds of gametes?

Answer 20

4

Question 21

A red bull is crossed with a white cow and all of the offspring are roan, an intermediate color that is caused by the presence of both red and white hairs. This is an example of genes that are _____.

Answer 21

codominant

Question 22

Flower color in snapdragons is an example of incomplete dominance. When a red-flowered plant is crossed with a white-flowered plant, the F1 generation has pink flowers. If a pink-flowered plant is crossed with another pink-flowered plant, the progeny plants will be _____.

Answer 22

25% red, 50% pink, and 25% white

Question 23

Which choice below describes the expression of Tay-Sachs disorder in humans at the biochemical level?

Answer 23

incompletely dominant

Question 24

Human blood groups are governed by three alleles, A, B, and O. A and B are codominant and O is recessive to both. A man who has type B blood and a woman who has type A blood could have children of which of the following phenotypes?

Answer 24

A, B, AB, or O

Question 25

Which of the following matings cannot produce a child with blood type O? The letters refer to blood types (phenotypes).

Answer 25

O × AB

-Both parents could be I^Ai.

Question 26

A woman with type O blood is expecting a child. Her husband is type A. Both the woman’s father and her husband’s father had type B blood. What is the probability that the child will have type O blood?

Answer 26

50%

Question 27

A single genetic locus that controls more than one trait is said to be _____.

Answer 27

pleiotropic

Question 28

Color in squash is controlled by epistatic interactions in which color is recessive to no color. At the first locus white squash (W) is dominant to colored squash (w). At the second locus yellow (Y) is dominant to green (y). What is the phenotype of a squash with the genotype wwYy?

Answer 28

yellow

Question 29

Tail length in a certain species of armadillo falls along a continuum, following a normal distribution. Assuming that environmental factors do not play an important role in determining tail length, this type of variation probably reflects _____.

Answer 29

polygenic inheritance

-Characters that vary along a continuum, following a normal distribution, are often controlled by multiple genes, each contributing to the phenotype in an additive fashion.

Question 30

Mendel’s theory of particulate inheritance _____.

Answer 30

can explain inheritance patterns for virtually every sexually reproducing organism but does not explain multifactorial characters

-Although many patterns of inheritance have been discovered, they can still be explained using the concept of alleles (Mendel’s hereditary “particles”). Multifactorial characters are influenced by environmental influences, so they are not strictly governed by Mendel’s theory.

Question 31

Tay-Sachs disease runs in Rebecca’s family. On a family pedigree, she saw a shaded circle. This represented a _____.

Answer 31

female with Tay-Sachs

Question 32

A man who can roll his tongue and a woman who cannot roll her tongue have a son who can roll his tongue (R = can roll tongue; r = can’t roll tongue). The son is curious about whether his father is homozygous or heterozygous for the tongue-rolling trait. Which of the following facts would allow him to know?

Answer 32

His father’s mother cannot roll her tongue.

-If his father’s mother cannot roll her tongue, then his father must be heterozygous.

Question 33

Michelle and Keith are apparently normal, but their daughter was born with alkaptonuria, an inherited metabolic disorder. If alkaptonuria is like most other human hereditary disorders, the probability of their next child being born with alkaptonuria is _____.

Answer 33

1/4

Question 34

Tom’s brother suffers from phenylketonuria (PKU), a recessive disorder. The brothers’ parents do not have PKU. What are the chances that Tom, who is normal for this trait, is a carrier of PKU?

Answer 34

2/3

Question 35

A couple, both descended from eastern European (Ashkenazic) Jews, visit a genetic counselor before trying to have children. In view of their ethnic background, the counselor recommends that they be tested to see if they are carriers for _____.

Answer 35

Tay-Sachs

Question 36

Cystic fibrosis, which is usually lethal before the age of reproduction, is a homozygous recessive trait. Why do cases continue to arise, even though people with the disease rarely live to reproduce?

Answer 36

The harmful allele “hides” within heterozygous individuals, and one-fourth of the offspring of two heterozygotes would be afflicted.

Question 37

The genetic disease cystic fibrosis is caused by a defective allele that _____.

Answer 37

encodes a defective chloride-channel membrane transport protein

Question 38

In people with sickle-cell disease, red blood cells break down, clump, and clog the blood vessels. The blood vessels and the broken cells accumulate in the spleen. Among other things this leads to physical weakness, heart failure, joint pain, and brain damage. Such a suite of symptoms can be explained by _____.

Answer 38

the pleiotropic effects of the sickle-cell allele

Question 39

When two average-height parents give birth to a child exhibiting achondroplasia, it is most likely due to a new mutation. This is because _____.

Answer 39

achondroplasia is caused by an allele that is always expressed, therefore the parents must not have the allele

Question 40

It is far more common to find human genetic disease caused by _____ alleles than by _____ alleles because _____.

Answer 40

recessive … dominant … harmful recessive alleles can survive in the heterozygote without any selection pressure against them

Question 41

Huntington’s disease is an example of a genetic disorder caused by _____.

Answer 41

a lethal dominant allele that afflicts an individual later in life

-By the time symptoms are evident, the individual may have already transmitted the allele to his or her children.

Question 42

Heart disease, diabetes, cancer, alcoholism, and many mental illnesses can best be described as _____.

Answer 42

multifactorial disorders with a possible polygenic component

Question 43

Fetal cells may be removed along with fluid from the womb by a process known as _____.

Answer 43

amniocentesis

Question 44

In which genetic testing procedure would a physician remove a small tissue sample from a membrane of fetal genetic origin?

Answer 44

chorionic villus sampling

-The cells sampled are derived from the fetus; therefore, a karyotype of the fetus can be created using these cells.

Question 45

How does codominance at the molecular level help to explain why evolutionary processes haven’t resulted in the elimination of the sickle-cell allele among people of African descent?

Answer 45

Individuals with normal and sickle-cell hemoglobin in their red blood cells are usually healthy and, when infected by the malaria parasite, have lower parasite densities and, thus, reduced malaria symptoms.

Question 46

What kind of protection does the Genetic Information Nondiscrimination Act of 2008 provide the public with regard to the use of genetic information?

Answer 46

The law prohibits the use of genetic test information to deny insurance coverage or employment to individuals.

Question 47

In his breeding experiments, Mendel first crossed true-breeding plants to produce a second generation, which were then allowed to self-pollinate to generate the offspring. How do we name these three generations?

Answer 47

P … F1 … F2

-Mendel started with true-breeding P generation plants, and in a typical experiment generated two subsequent generations, called F1 and F2.

Question 48

Which of the following is true about a plant with the genotype AABbcc?

Answer 48

It is homozygous at two loci.

-An organism having a pair of identical alleles at a given locus is said to be homozygous for that locus. Here, the plant is homozygous at loci A and C.

Question 49

What is an allele?

Answer 49

an alternative version of a gene

-A diploid organism carries two alleles for each autosomal gene. The two alleles are found at comparable locations (loci) on homologous chromosomes. The alleles may be identical or slightly different, but they affect the same genetic character.

Question 50

Consider pea plants with the genotypes GgTt and ggtt . These plants can each produce how many type(s) of gametes?

Answer 50

four … one

-GgTt individuals can produce the following gametes: GT, Gt, gT, and gt. A ggtt plant can produce only gt.

Question 51

Two organisms with genotype AaBbCcDdEE mate. These loci are all independent. What fraction of the offspring will have the same genotype as the parents?

Answer 51

1/16

-Breaking the question down into individual loci makes it simpler. The offspring of Aa ×Aa will be Aa 50% (one-half) of the time. The same is true for Bb, Cc, and Dd. Two EE individuals can only have EE offspring, so that probability is 1. The chance of an offspring being identical to the parent is therefore (1/2)4, or 1/16.

Question 52

You cross a true-breeding red-flowered snapdragon with a true-breeding white-flowered one. All of the F1 are pink. What does this say about the parental traits?

Answer 52

Red shows incomplete dominance over white.

-Red shows incomplete dominance over white, and the F1 is therefore pink.

Question 53

Height in humans generally shows a normal (bell-shaped) distribution. What type of inheritance most likely determines height?

Answer 53

a combination of polygenic inheritance and environmental factors

-Several genes (polygenic inheritance) control height in humans, giving an overall normal distribution. Environmental factors such as nutrition smooth out the curve.

Question 54

Folk singer Woody Guthrie died of Huntington’s disease, an autosomal dominant disorder. Which statement below must be true?

Answer 54

It is very likely that at least one of Woody Guthrie’s parents also have had the allele for Huntington’s disease.

-Unless the disease is caused by a new mutation, which is quite rare, individuals with a dominant condition must have inherited the dominant allele from one of their parents. As it happens, Guthrie’s mother also died of Huntington’s disease.

Question 55

Various procedures can be used to detect genetic disorders before birth. Among the tests discussed in this chapter, which is the least invasive (list first), and which two allow the chromosomes of the fetus to be examined?

Answer 55

ultrasound imaging … chorionic villus sampling … amniocentesis

-Both CVS and amniocentesis involve the preparation of a karyotype using fetal cells.

Question 56

Which of the following do you expect if an individual is heterozygous for the sickle-cell trait?

Answer 56

He or she will show some symptoms of the disease.

-A heterozygote will produce both normal and abnormal hemoglobin.

Question 57

What is the difference between heterozygous and homozygous individuals?

Answer 57

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

-Since homozygotes carry two identical copies of a gene, all of the gametes will carry the same version. Heterozygotes have two different versions, so there will be two different types of gametes.

Question 58

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

Answer 58

gametes, progeny

-The Punnett square is representing all of the possible combinations of the gametes from each parent, with the progeny represented in the interior of each box.

Question 59

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

Answer 59

True

-Since there exist dominant and recessive versions of many genes, a phenotype that is based upon the dominant version will be expressed in both homozygous (AA) and heterozygous (Aa) genotypes.

Question 60

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

Answer 60

False

-A dominant phenotype is indeed expressed if the individual is homozygous dominant for that trait, but the dominant phenotype is also expressed if the individual is heterozygous for the trait. In fact, heterozygous expression is the definition of dominant.

Question 61

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

Answer 61

None

-Alleles of the same gene must separate during gamete formation; thus, the two B alleles would be distributed to different gametes.

Question 62

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 62

25

-The offspring would be in a 3:1 ratio of normally pigmented mice to albino mice.

Question 63

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 63

ttpp

-The smallest phenotypic group consists of the homozygous recessive plants, which in this case are short and white flowered.

Question 64

What process is responsible for the independent assortment of alleles?

Answer 64

Meiosis

-The role of meiosis is to separate homologous chromosomes and their respective alleles, which are assorted in an independent manner.

Question 65

How do cells acquire homologous chromosome pairs that carry the alleles that are independently assorted?

Answer 65

Fusion of gametes

-During fertilization, gametes bring together homologous chromosomes to generate a diploid individual.

Question 66

Which of the following statements most accurately describes the process of independent assortment?

Answer 66

Alleles of different genes segregate from one another in a random manner.

-The random distribution of alleles is required for independent assortment.

Question 67

True or false? The principle of independent assortment is best illustrated by events that take place during metaphase II, during which sister chromatids segregate independently of each other.

Answer 67

False

-The principle of independent assortment is best illustrated by events that take place during metaphase I, during which nonhomologous chromosomes segregate independently of each other.

Question 68

How many genetically unique types of gametes could be produced by an individual with the genotype RrYY?

Answer 68

Two

-The gametes would be either RY or rY.

Question 69

Which of the following parental genotypes would yield a 1:1:1:1 phenotypic ratio in the offspring?

Answer 69

AaBb, aabb

-The offspring of these parents would have a phenotypic ratio of 1:1:1:1.

Question 70

Mendel worked _____.

Answer 70

in a monastery

-Mendel was a monk who worked in his monastery garden.