Biological Science

Scott Freeman, Lizabeth Allison, Michael Black

Chapter 14

Mendel and the Gene - all with Video Answers

Educators

Chapter Questions

Problem 1

In studies of how traits are inherited, what makes certain species candidates for model organisms?
a. They are the first organisms to be used in a particular type of experiment, so they are a historical "model" of what researchers expect to find.
b. They are easy to study because a great deal is already known about them.
c. They are the best or most fit of their type.
d. They are easy to maintain, have a short life cycle, produce many offspring, and yield data that are relevant to many other organisms.

Chelsi Marolf

Chelsi Marolf

Numerade Educator

Problem 2

Why is the allele for wrinkled seed shape in garden peas considered recessive?
a. It "recedes" in the $\mathrm{F}_{2}$ generation when homozygous parents are crossed.
b. The trait associated with the allele is not expressed in heterozygotes.
c. Individuals with the allele have lower fitness than that of individuals with the dominant allele.
d. The allele is less common than the dominant allele. (The wrinkled allele is a rare mutant.

Chelsi Marolf

Numerade Educator

Problem 3

The alleles found in haploid organisms cannot be dominant or recessive. Why?
a. Dominance and recessiveness describe which allele is expressed in phenotype when different alleles occur in the same individual.
b. Because only one allele is present, alleles in haploid organisms are always dominant.
c. Alleles in haploid individuals are transmitted like mitochondrial DNA or chloroplast DNA.
d. Most haploid individuals are bacteria, and bacterial genetics is completely different from eukaryotic genetics.

Chelsi Marolf

Numerade Educator

Problem 4

Why can you infer that individuals that are "pure line" are homozygous for the gene in question?
a. Because they are highly inbred.
b. Because only two alleles are present at each gene in the populations to which these individuals belong.
c. Because in a pure line, phenotypes are not affected by environmental conditions or gene interactions.
d. Because no other phenotype is ever observed in a pure-line population, this implies that only one allele is present.

Chelsi Marolf

Numerade Educator

Problem 5

The genes for the traits that Mendel worked with are either located on different chromosomes or so far apart on the same chromosome that crossing over almost always occurs between them. How did this circumstance help Mendel recognize the principle of independent assortment?
a. Otherwise, his dihybrid crosses would not have produced a 9: 3: 3: 1 ratio of $\mathrm{F}_{2}$ phenotypes
b. The occurrence of individuals with unexpected phenotypes led him to the discovery of recombination.
c. It led him to the realization that the behavior of chromosomes during meiosis explained his results.
d. It meant that the alleles involved were either dominant or recessive, which gave 3: 1 ratios in the $F_{1}$ generation.

Chelsi Marolf

Numerade Educator

Problem 6

What is meant by the claim that Mendel worked with the simplest possible genetic system?
a. Discrete traits, two alleles, simple dominance and recessiveness, no sex chromosomes, and unlinked genes are the simplest situation known.
b. The ability to self-fertilize or cross-pollinate made it simple for Mendel to set up controlled crosses.
c. Mendel was aware of meiosis and the chromosome theory of inheritance, so it was easy to reach the conclusions he did.
d. Mendel's experimental designs and his rules of inheritance are actually neither complex nor sophisticated.

Chelsi Marolf

Numerade Educator

Problem 7

Mendel's rules do not correctly predict patterns of inheritance for tightly linked genes or the inheritance of alleles that show incomplete dominance. Does this mean that his hypotheses are incorrect?
a. Yes, because they are relevant to only a small number of organisms and traits.
b. Yes, because not all data support his hypotheses.
c. No, because he was not aware of meiosis or the chromosome theory of inheritance.
d. No, it just means that his hypotheses are limited to certain conditions.

Chelsi Marolf

Numerade Educator

Problem 8

The artificial sweetener NutraSweet consists of a phenylalanine molecule linked to aspartic acid. The labels of diet sodas that contain NutraSweet include a warning to people with PKU. Why?
a. NutraSweet stimulates the same taste receptors that natural sugars do.
b. People with PKU have to avoid phenylalanine in their diet.
c. In people with $\mathrm{PKU}$, phenylalanine reacts with aspartic acid to form a toxic compound.
d. People with PKU cannot lead normal lives, even if their environment is carefully controlled.

Satpal Satpal

Numerade Educator

Problem 9

When Sutton and Boveri published the chromosome theory of inheritance, research on meiosis had not yet established that paternal and maternal homologs of different chromosomes assort independently. Then, in 1913 , Elinor Carothers published a paper about a grasshopper species with an unusual karyotype:
One chromosome had no homolog (meaning no pairing partner at meiosis I); another chromosome had homologs that could be distinguished under the light microscope. If chromosomes assort independently, how often should Carothers have observed each of the four products of meiosis shown in the following figure?
a. Only the gametes with one of each type of chromosome would occur
b. The four types of gametes should be observed to occur at equal frequencies.
c. The chromosome with no pairing partner would disintegrate, so only gametes with one copy of the other chromosome would be observed.
d. Gametes with one of each type of chromosome would occur twice as often as gametes with just one chromosome.

Chelsi Marolf

Numerade Educator

Problem 10

Which of the following is the strongest evidence that a trait might be influenced by polygenic inheritance?
a. $F_{1}$ offspring of parents with different phenotypes have an intermediate phenotype.
b. $\mathrm{F}_{1}$ offspring of parents with different phenotypes have the dominant phenotype
c. The trait shows qualitative (discrete) variation.
d. The trait shows quantitative variation.

Chelsi Marolf

Numerade Educator

Problem 11

Plectritis congesta plants produce fruits that either have or do not have prominent structures called wings. The alleles involved are $W^{+}=$ winged fruit; $W^{-}=$ wingless fruit. Researchers collected an array of individuals from the field and performed a series of crosses. The results are given in the following table. Complete the table by writing down the genotype of the parent or parents involved in each cross.
$$\begin{array}{lccc}\text { Parental } & \text { Number of } & \text { Number of } & \\\text { Phenotype(s) } & \text { Offspring with } & \text { Offspring with } & \text { Parental } \\\text { Wingless } & \text { Winged Fruits } & \text { Wingless Fruits } & \text { Genotype(s) } \\\text { (self-fertilized) } & & & \\\text { Winged } & 90 & 30 & \\\text { (self-fertilized) } & & & \\\text { Winged } \times & 46 & 0 & \\\text { wingless } & & & \\\begin{array}{l}\text { Winged } \times \\\text { winged }\end{array} & 44 & 0 & \\\hline\end{array}$$

John Barone

Numerade Educator

Problem 12

Two black female mice are crossed with a brown male. In several litters, female I produced 9 blacks and 7 browns; female II produced 57 blacks. What deductions can you make concerning the inheritance of black and brown coat color in mice? What are the genotypes of the parents in this case?

Chelsi Marolf

Numerade Educator

Problem 13

In peas, purple flowers are dominant to white. If a purpleflowered, heterozygous plant were crossed with a white-flowered plant, what is the expected ratio of genotypes and phenotypes among the $\mathrm{F}_{1}$ offspring? If two of the purple-flowered $\mathrm{F}_{1}$ offspring were randomly selected and crossed, what is the expected ratio of genotypes and phenotypes among the $\mathrm{F}_{2}$ offspring?

Chelsi Marolf

Numerade Educator

Problem 14

In garden peas, yellow seeds ( $Y$ ) are dominant to green seeds $(y),$ and inflated pods $(I)$ are dominant to constricted pods $(i)$ Suppose you have crossed YYII parents with $y$ yii parents.
Draw the $\mathrm{F}_{1}$ Punnett square and predict the expected $\mathrm{F}_{1}$ phenotype(s).
List the genotype(s) of gametes produced by $\mathrm{F}_{1}$ individuals.
Draw the $F_{2}$ Punnett square. Based on this Punnett square, predict the expected phenotype(s) in the $\mathrm{F}_{2}$ generation and the expected frequency of each phenotype.

Chelsi Marolf

Numerade Educator

Problem 15

The smooth feathers on the back of the neck in pigeons can be reversed by a mutation to produce a "crested" appearance in which feathers form a distinctive spike at the back of the head. A pigeon breeder examined offspring produced by a single pair of noncrested birds and recorded the following: 22 non-crested and 7 crested. She then made a series of crosses using offspring from the first cross. When she crossed two of the crested birds, all 20 of the offspring were crested. When she crossed a non-crested bird with a crested bird, 7 offspring were non-crested and 6 were crested.
For these three crosses, provide genotypes for parents and offspring that are consistent with these results.
Which allele is dominant?

Chelsi Marolf

Numerade Educator

Problem 16

A plant with orange, spotted flowers was grown in the greenhouse from a seed collected in the wild. The plant was self-pollinated and gave rise to the following progeny: 88 orange with spots, 34 yellow with spots, 32 orange with no spots, and 8 yellow with no spots. What can you conclude about the dominance relationships of the alleles responsible for the spotted and unspotted phenotypes? For the orange and yellow phenotypes? What can you conclude about the genotype of the original plant that had orange, spotted flowers?

Chelsi Marolf

Numerade Educator

Problem 17

As a genetic counselor, you routinely advise couples about the possibility of genetic disease in their offspring based on their family histories. This morning you met with an engaged couple, both of whom are phenotypically normal. The man, however, has a brother who died of Duchenne-type muscular dystrophy, an X-linked condition that results in death before the age of 20 . The allele responsible for this disease is recessive. His prospective bride, whose family has no history of the disease, is worried that the couple's sons or daughters might be afflicted.
How would you advise this couple?
The sister of this man is planning to marry his fiancée's brother. How would you advise this second couple?

Chelsi Marolf

Numerade Educator

Problem 18

Suppose you are heterozygous for two genes that are located on different chromosomes. You carry alleles $A$ and $a$ for one gene and alleles $B$ and $b$ for the other. Draw a diagram illustrating what happens to these genes and alleles when meiosis occurs in your reproductive tissues. Label the stages of meiosis, the homologous chromosomes, sister chromatids, nonhomologous chromosomes, genes, and alleles. Be sure to list all the genetically different gametes that could form and indicate how frequently each type should be observed. On the diagram, identify the events responsible for the principle of segregation and the principle of independent assortment.

Christina Sorrentino

Christina Sorrentino

Numerade Educator

Problem 19

Review the text's description of ABO blood types. Suppose a woman with blood type $\mathrm{O}$ married a man with blood type $\mathrm{AB}$. What phenotypes and genotypes would you expect to observe in their offspring, and in what proportions? Answer the same question for a heterozygous mother with blood type $A$ and $a$ heterozygous father with blood type B.

Chelsi Marolf

Numerade Educator

Problem 20

An alien friend named Tukan has two sets of eyes, one set forward-looking and one set backward-looking, and smooth skin. His mate, Valco, lacks eyes but has skin covered with tiny hooks that attract all sorts of debris. Tukan and Valco have thrived on earth and have had four children, all with no eyes and smooth skin. Typical of their ways, the children interbred and produced 32 children of their own.
Under the models of inheritance proposed by Mendel, identify which alleles are dominant and which are recessive.
Provide gene symbols that would reflect the dominant-recessive allelic relationships.
Of the 32 children, how many would you expect to have two sets of eyes and smooth skin?

Nicole Hewett

Numerade Educator

Problem 21

Phenylketonuria (PKU) is a genetic disease caused by homozygosity for a recessive mutation in the enzyme that converts the amino acid phenylalanine to tyrosine. In the absence of this enzyme, phenylalanine and some of its derivatives accumulate in the body and cause mental retardation. If individuals are identified soon enough after birth, they can be treated by a lowphenylalanine diet for the early years of their lives. As adults, though, homozygous recessive individuals are allowed to adopt a diet with normal amounts of phenylalanine. Not long after such treatments were initiated, a troubling phenomenon was observed. A high number of children born to treated mothers were mentally retarded even though the children were heterozygous for the PKU gene. Children born of treated PKU males suffered no ill effects.
Can you offer an explanation as to why genetically heterozygous children of treated PKU mothers might be prone to mental retardation?
Propose a solution to reduce the likelihood of mental retardation in children of treated PKU mothers.

Cody Delk

Numerade Educator

Problem 22

The blending-inheritance hypothesis proposed that the genetic material from parents is unavoidably and irreversibly mixed in the offspring. As a result, offspring and later descendants should always appear intermediate in phenotype to their forebears. Mendel, in contrast, proposed that genes are discrete and that their integrity is maintained in the offspring and in subsequent generations. Suppose the year is $1890 .$ You are a horse breeder and have just read Mendel's paper. You don't believe his results, however, because you often work with cremello (very lightcolored and chestnut (reddish-brown) horses. You know that if you cross a cremello individual from a pure-breeding line with a chestnut individual from a pure-breeding line, the offspring will be palomino-meaning they have an intermediate (golden-yellow) body color. What additional crosses would you do to test whether Mendel's model is valid in the case of genes for horse color? List the crosses and the offspring genotypes and phenotypes you'd expect to obtain. Explain why these experimental crosses would provide a test of Mendel's model.

Chelsi Marolf

Numerade Educator

Problem 23

Two mothers give birth to sons at the same time in a busy hospital. The son of couple 1 is afflicted with hemophilia $A$, which is a recessive X-linked disease. Neither parent has the disease. Couple 2 has a normal son even though the father has hemophilia A. The two couples sue the hospital in court, claiming that a careless staff member swapped their babies at birth. You appear in court as an expert witness. What do you tell the jury? Make a diagram that you can submit to the jury.

Chelsi Marolf

Numerade Educator

Problem 24

You have crossed two Drosophila melanogaster individuals that have long wings and red eyes- the wild-type phenotype. In the progeny, the mutant phenotypes called curved wings and lozenge eyes appear as follows:
$$\begin{array}{ll}\text { Females } & \text { Males } \\\hline 600 \text { long wings, red eyes } & 300 \text { long wings, red eyes } \\
200 \text { curved wings, red eyes } & 100 \text { curved wings, red eyes } \\& 300 \text { long wings, lozenge eyes } \\
& 100 \text { curved wings, lozenge eyes } \\\hline\end{array}$$
According to these data, is the curved-wing allele autosomal recessive, autosomal dominant, sex-linked recessive, or sexlinked dominant?
Is the lozenge-eyed allele autosomal recessive, autosomal dominant, sex-linked recessive, or sex-linked dominant? What is the genotype of the female parent? What is the genotype of the male parent?

Chelsi Marolf

Numerade Educator

Problem 25

In parakeets, two autosomal genes that are located on different chromosomes control the production of feather pigment. Gene $B$ codes for an enzyme that is required for the synthesis of a blue pigment, and gene $Y$ codes for an enzyme required for the synthesis of a yellow pigment. Recessive mutations that result in no production of the affected pigment are known for both genes. Suppose that a bird breeder has two green parakeets and mates them. The offspring are green, blue, yellow, and albino (unpigmented).
Based on this observation, what are the genotypes of the green parents? What is the genotype of each type of offspring? What fraction of the total progeny should exhibit each type of color?
Suppose that the parents were the progeny of a cross between two true-breeding strains. What two types of crosses between true-breeding strains could have produced the green parents? Indicate the genotypes and phenotypes for each cross.

Joanna Quigley

Numerade Educator

Problem 26

Recall that hemophilia is an X-linked recessive disease. If a woman with hemophilia had children with a man without hemophilia, what is the chance that their first child will have the disease? What is the chance that their first child will be a carrier?

Chelsi Marolf

Numerade Educator