Biology Now, 2e

152 ■ CHAPTER 08 Chromosomes and Human Genetics

(^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 (GG, Gg, gg).
Female Male Unaffected
individual
Affected
individual

1 2

1 2 3 4 5 6

1 2 3 4

Generation

I

II

III

a. Generation I, number 2

b. Generation II, number 1

c. Generation II, number 2

d. Generation III, number 3

Leveling Up

(^14) Write Now biology: debating preimplantation genetic diagnosis
(PGD) 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 recommen-
dation for legislation.
Choose one of the following special-interest groups to repre-
sent (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.
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 tt.
(b) They are both Tt and tt.
(c) They are both Tt and TT.
(d) They must all be Tt.
(^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?
(^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 (XGY, XgY, XGXG,
XGXg, XgXg).
Female Male Unaffected
individual
Affected
individual

1

1 2 3 4 5 6

1 2 3 4 5 6 7

2

Generation

I

II

III

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