Chapter 14 Section Review
Answer key
Section Review 14-1
1. Two copies of the X chromosome produces a
human female. 2. One X and one Y chromosome produce a human male. 3. A sperm cell, which contains
either a Y or an X chromosome, determines whether a
child is male or female. 4. Half of the sperm cells that
fertilize eggs carry an X chromosome and half carry a
Y chromosome. Because all egg cells carry an X chromosome, half of all zygotes will be XX and half will be XY. 5. In cystic fibrosis, the deletion of three bases in the middle of a single gene changes the protein’s structure. 6. The father and both daughters show the trait. 7. The father and both daughters carry the allele for the trait. 8. The mother and the son do not carry the allele for the trait. 9. The IA allele leads to the production of the Aantigen. IB leads to the B antigen.
Because both alleles contribute to the phenotype, they
are said to be codominant.
Section Review 14-2
1. A sex-linked disorder is one that is caused by a
defective gene on an X or Y chromosome. 2. A single
recessive allele is expressed in a male when it is
found on the male’s X chromosome. 3. There must
be two copies of the allele, one on each of the two X
chromosomes, for a trait controlled by a recessive
allele to be expressed in females. 4. Nondisjunction
leads to the production of gametes with abnormal
numbers of chromosomes. 5. Klinefelter’s syndrome
6. Down syndrome 7. Turner’s syndrome 8. There
have been no reported instances of babies being born
without an X chromosome. Babies have been born
without a Y chromosome. 9. Her mother either has
hemophilia (two recessive alleles) or carries one
recessive allele for hemophilia. Her father has the
recessive allele and hemophilia. 10. Because the
woman’s father is colorblind, she will carry one
recessive allele for colorblindness. Their daughters
have a 100 percent chance of having normal vision,
because they will inherit the dominant allele for normal
vision from their father. Their sons have a 50 percent
chance of being colorblind. They have a 50
percent chance of inheriting the dominant allele for
normal vision and a 50 percent chance of inheriting
the recessive allele for colorblindness.
Section Review 14-3
1. The goal of the Human Genome Project is to analyze
the human DNA sequence. 2. Gene therapy is
the process of replacing an absent or faulty gene with
a normal, working gene in an attempt to cure a genetic
disorder. 3. Modified viruses are often used to
deliver replacement genes. 4. normal hemoglobin
gene 5. genetically engineered virus 6. bone marrow
cell 7. bone marrow 8. DNAsamples from the
victim and the suspect would be compared to the
DNAin the blood. All three samples would be cut
with the same restriction enzymes, targeting small
sections of DNA with little or no known function. The
DNAfragments would be separated by gel electrophoresis. The banding pattern from the individual
that matches the banding pattern for the blood is
identified as the person whose blood was at the scene.
9. Possible student answers may include: An ethical
way to manipulate DNA would be to change DNA to
cure a genetic disease, such as Tay-Sachs or cystic
fibrosis. This application is ethical only if it benefits
humans without harming others. An unethical way to
manipulate DNA might be to clone human beings so
that their organs could be harvested for transplant
recipients.
Chapter Vocabulary Review
1. karyotype 2. sex chromosomes 3. autosomes
4. pedigree 5. nondisjunction 6. d 7. b 8. b 9. a
10. a 11. d 12. A karyotype will show whether or
not a fetus has Down syndrome. 13. Because the X
and Y chromosomes present in the embryo determine
the sex of the child. 14. There are 44 autosomes in a
human diploid cell. 15. A pedigree chart shows how
a trait is passed from one generation to the next.
.
Graphic Organizer
1. Autosomal genetic disorders are caused by abnormal
dominant, codominant, or recessive alleles on the
autosomes. 2. Examples include Phenylketonuria,
Tay-Sachs, Huntington’s disease, Cystic fibrosis, and
Sickle cell disease. 3. Yes (Affects males more often
than females, but can affect females if they inherit
two recessive alleles.) 4. Chromosomal disorders are
caused by nondisjunction during meiosis, which
results in an abnormal number of chromosomes.
5. Down syndrome, Klinefelter’s syndrome, Turner’s
syndrome