Biology Now

Anne Houtman; Megan Scudellari; Cindy Malone

Chapter 8

Chromosomes and Human Genetics - all with Video Answers

Educators

Chapter Questions

Problem 1

Use these terms correctly in the following sentence: alleles, chromosomes, genes, loci. Two homologous ______ contain the same ________ found at the same _______ but may have the same or different copies of ____.

Joanna Quigley

Joanna Quigley

Numerade Educator

Problem 2

A particular person is said to be a carrier of a genetic trait. What does this tell you about their phenotype?
(a) They physically show the trait.
(b) They physically show the trait more than a noncarrier would show the trait.
(c) They are almost normal but show an intermediate phenotype for the trait.
(d) They are completely normal and do not physically show the trait.

Joanna Quigley

Numerade Educator

Problem 3

Match each of the following terms with the correct definition.
GENE THERAPY
IN VITRO FERTILIZATION
PREIMPLANTATION GENETIC DIAGNOSIS (PGD]
CHORIONIC VILLUS SAMPLING (cvs)
AMNIOCENTESIS
1. A procedure in which cells are gently suctioned from a pregnant woman's uterus to test for genetic disorders in the fetus.
2. A procedure in which a small amount of fluid [and fetal cells within it) is carefully extracted from a pregnant woman's uterus to test for genetic disorders in the fetus.
3. A treatment approach that seeks to correct a genetic disorder by inserting healthy copies of the mutated genes responsible for the disorder.
4. A procedure in which one or two cells are removed from a developing embryo and tested for genetic disorders; embryos that are free of genetic disorders may then be implanted into a woman's uterus.
5. A procedure in which an $\mathrm{egg}$ is fertilized in a petri dish, after which one or more embryos are implanted into a woman's uterus.

Joanna Quigley

Numerade Educator

Problem 4

In the karyotype shown here, identify the sex chromosomes. Is this individual a male or a female?

Joanna Quigley

Numerade Educator

Problem 5

Sickle-cell disease is inherited as a recessive genetic disorder in humans; the normal hemoglobin allele $[H)$ is dominant to the sicklecell allele (h]. For two parents of genotype Hh (carriers), construct a Punnett square to show the possible genotypes of their children.

Joanna Quigley

Numerade Educator

Problem 6

Which of the following correctly predicts the possible genotypes of the children from question $5 ?$
[a) $1 / 4 \mathrm{HH}, 1 / 4 \mathrm{Hh}, 1 / 2 \mathrm{hh}$
(b) $1 / 2 \mathrm{HH}, 1 / 2 \mathrm{Hh}$
(c) $1 / 2 \mathrm{HH}, 1 / 2 \mathrm{hh}$
(d) $1 / 4 \mathrm{HH}, 1 / 2 \mathrm{Hh}, 1 / 4 \mathrm{hh}$
(e) $1 / 4 \mathrm{HH}, 3 / 4 \mathrm{Hh}$

Joanna Quigley

Numerade Educator

Problem 7

Which of the following correctly predicts the possible phenotypes of the children from question $5 ?$
(a) $1 / 4$ normal, $3 / 4$ sickle-cell disease
(b) all normal
(c) all sickle-cell disease
(d) $1 / 2$ normal, $1 / 2$ sickle-cell disease
(e) $3 / 4$ normal, $1 / 4$ sickle-cell disease

Joanna Quigley

Numerade Educator

Problem 8

Given that the normal hemoglobin allele $(H)$ is dominant to the sickle-cell allele (h), each time two Hh individuals have a child together, what is the chance that the child will have sickle-cell disease?
(a) $0 \%$
(b) $75 \%$
(c) $25 \%$
(d) $50 \%$
[e) $100 \%$

Joanna Quigley

Numerade Educator

Problem 9

Which of the following karyotypic sex chromosome abnormalities result(s) in a male phenotype? (Select all that apply.)
(a) $x 0$
(b) $X X Y$
(c) $\mathrm{XXX}$
(d) XYY
(e] $X X X Y$
(f) XY with a complete deletion of the SRY gene

Joanna Quigley

Numerade Educator

Problem 10

On the Indonesian island of Bali, about $3 / 4$ of the feral (stray) cats have a stumpy tail, while only $1 / 4$ of the cats have a long tail. Experiments in which a bunch of random stumpy-tailed cats were mated with each other yielded some stumpy-tailed kittens and some long-tailed kittens. The same experiments with long-tailed cats produced only long-tailed kittens. What do these results show about the genotype of the long-tailed cats? (Hint: Draw Punnett squares using the letter "t" for the tail trait to help you determine which allele is dominant and which is recessive.)
(a) They must all be $t$ t.
(b) They are both $T t$ and $t t$.
(c) They are both $T t$ and $T T$.
(d) They must all be $T t$.

Joanna Quigley

Numerade Educator

Problem 11

Recall that human females have two X chromosomes, while human males have one $X$ chromosome and one $Y$ chromosome.
a. Do males inherit their $X$ chromosome from their mother or from their father?
b. If a female has one copy of an X-linked recessive allele for a genetic disorder, does she have the disorder?
c. If a male has one copy of an X-linked recessive allele for a genetic disorder, does he have the disorder?
d. Assume that a female is a carrier of an X-linked recessive disorder. With respect to the disorder allele, how many types of gametes can she produce?
e. Assume that a male with an X-linked recessive genetic disorder has children with a female who does not carry the disorder allele. Could any of their sons have the genetic disorder? How about their daughters? Could any of their children be carriers for the disorder? If so, which sex[es) could they be?

Joanna Quigley

Numerade Educator

Problem 12

For the pedigree shown here, the disorder is caused by a recessive (g) allele on the X chromosome. Label each of the following individuals with the correct genotype $\left(X^{G} Y, X^{E} Y, X^{G} X^{G}\right.$ $\mathrm{X}^{G} \mathrm{X}_{\mathrm{g}}, \mathrm{X} \mathrm{E} \mathrm{X}^{\mathrm{B}}$ ].
a. Generation I, number 2
b. Generation II, number 2
c. Generation II, number 5
d. Generation III, number 2
e. Generation III, number 6

Joanna Quigley

Numerade Educator

Problem 13

For the pedigree shown here, the disorder is caused by a recessive (g) autosomal allele. Label each of the following individuals with the correct genotype $[G G, G g, g g]$
a. Generation I, number 2
b. Generation II, number 1
c. Generation II, number 2
d. Generation III, number 3

Joanna Quigley

Numerade Educator

Problem 14

This assignment is designed to give you the experience of applying your knowledge of biology to a current controversy or topic of interest. You will apply the same sort of reasoning that you should be able to use as an informed citizen and consumer when making decisions that involve biology. The scenario: The U.S. Senate Committee on Commerce, Science and Transportation (CCST) is considering proposing legislation on preimplantation genetic diagnosis (PGD; see "Prenatal Genetic Screening" on page 148). The chair of the committee has invited special-interest groups to present testimony on the pros and cons of PGD. You will contribute a position paper defining PGD, describing your group's position on the technology, and making a recommendation for legislation.

Choose one of the following special-interest groups to represent [or your instructor will assign one to you]:
(a) Reproductive Specialist Group (medical doctors]. You will describe how PGD and in vitro fertilization (IVF) can be used to screen for genetic disorders or for sex selection and "family balancing," and to increase fertility in women of advanced maternal age. You will argue that legislation is not necessary, since medical association guidelines are already in place, and that it is not the place of government to judge individuals reasons for undergoing PGD.
(b) Genetics and Public Policy Group. You will present data on the beliefs of the American public in this matter. You will also present the status of current legislation in the United States and how it compares to PGD legislation internationally. You will propose limited legislation based on these findings.
(c) Parents of Down Syndrome Children. You will argue that people with disabilities already suffer from prejudice, and that widespread use of such testing will cause even more prejudice. You will propose legislation prohibiting PGD for almost all conditions, with the exception of deadly, infant-onset disease.
(d) Americans with Cystic Fibrosis. You will present the case of a couple, both of whom are carriers for CF, and discuss their options. You will propose limited legislation that disallows PGD for sex selection and nondisease conditions.

Joanna Quigley

Numerade Educator

Problem 15

What do you think? Gattaca, a science fiction movie from 1997, is based in a future in which preimplantation genetic diagnosis (PGD) is used to create genetically superior children, and social status is determined mainly by one's DNA. Watch the movie and take careful notes as you observe how PGD has been misused by society. Do you think these outcomes are likely, if we continue to develop PGD? Are the benefits worth this risk?

Joanna Quigley

Numerade Educator

Problem 16

While you cannot control the genes that you inherited from your parents, you can control your exposure to external factors that increase your chances of developing a disease that is only partially genetically determined. For this assignment, you will estimate your life expectancy, as determined mainly from your lifestyle choices. Go to the "Living to $100^{\prime \prime}$ website (http://www.livingto100.com) and complete the Life Expectancy Calculator. Answer all questions honestly (no one will see your answers), and go to the "feedback" page at the end of the questionnaire. Take notes so that you can answer the following questions.
a. What is your calculated life expectancy, given the answers you gave?
b. List the recommendations to increase your life expectancy, and how much they could increase your life span.
c. What change would increase your life span the most?
d. Identify one way that you could feasibly increase your life span. Will you do that? Why or why not?

Joanna Quigley

Numerade Educator