402 Chapter 20
- If a trait appears only in males, is this good evidence that
the trait is due to a Y-linked allele? Explain why you
answered as you did. - A woman unaffected by hemophilia A whose father had
hemo philia A marries a man who also has hemophilia A. If
their first child is a boy, what is the probability he will have
the disorder? - About 4 percent of people of Northern European descent
have a cystic fibrosis allele, but only about 1 in 2,500 of
these people actually has the disorder. What is the most
likely reason for this finding? - The following pedigree shows the pattern of inheritance of
red–green color blindness in a family. Females are shown
as circles and males as squares; the squares or circles of
individuals affected by the trait are filled in black. What
is the chance that a son of the third-generation female
indicated by the arrow will be color blind if the father is
not color blind? If he is color blind? - Genetic disorders can be caused by.
a. gene mutations
b. changes in chromosome structure
c. changes in chromosome number
d. all of the above - A person who is a carrier for a genetic trait.
a. is heterozygous for a dominant trait
b. is heterozygous for a recessive trait
c. is homozygous for a recessive trait
d. could be either a or b but not c - Match the following chromosome terms appropriately.
crossing over a. a chemical change in DNA
deletion that may affect genotype
nondisjunction and phenotype
translocation b. movement of a chromosome
gene mutation segment to a nonhomologous
chromosome
c. disrupts gene linkages
during meiosis
d. causes gametes to have
abnormal chromosome
numbers
e. loss of a chromosome segment
CritiCaL thinKinG
- If a couple has six boys, what is the probability that a
seventh child will be a girl? - Human sex chromosomes are XX for females and XY
for males.
a. With respect to an X-linked gene, how many different
types of gametes can a male produce?
b. If a female is homozygous for an X-linked allele, how
many different types of gametes can she produce with
respect to this allele?
c. If a female is heterozygous for an X-linked allele, how
many different types of gametes can she produce with
respect to this allele? - People with Down syndrome have an extra copy of
chromosome 21, for a total of 47 chromosomes. However,
in a few cases of Down syndrome, 46 chromosomes are
present. This total includes two normal-looking chromo-
somes 21, one normal chromosome 14, and a longer-
than-normal chromosome 14. Interpret this observation.
How can these individuals have 46 chromosomes? © Cengage Learning
Medical treatment tailored
to a patient’s genetic
makeup is becoming
more common, especially
in the treatment of some
cancers. One obstacle
remaining is the length
of time it currently takes
to analyze genes. Much
faster testing methods are
being developed, however.
It may not be long before
personalized medicine is
much more widely available.your future
From “Multicolor Spectral Karyotyping of Human Chromosomes” by E. Schrock, T. Ried, et al.,Science, 26 July 1996, Volume 273, p.- Used by permission of E. Schrock and T. Ried and The American Association for the Advancement of Science
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