Download Chapter 13 Chromosomes

Chapter 13 Chromosomes
Answers to Review Questions
1.
Essential parts of a chromosome are telomeres, the centromere, and origin of replication
sites. A centromere includes repeats of alpha satellites; centromere-associated proteins; and
centromere protein A.
2.
The centromeres and telomeres are important in an evolutionary sense because their
repetitive structure is similar among species.
3.
Protein-encoding genes become denser from the telomeres inward toward the centromere.
4.
Centromeres and telomeres contribute to chromosome stability and have many repeats.
5.
euploid = correct chromosome # aneuploid = missing or extra chromosome polyploidy =
extra chromosome sets
6.
a.
Homologs do not separate in meiosis I or II, leading to a gamete with an extra or
missing chromosome.
b.
DNA replicates, but is not apportioned into daughter cells, forming a diploid
gamete.
c.
Increased tendency for nondisjunction in the chromosome 21 pair.
d.
Crossing over in the male yields unbalanced gametes, which can fertilize oocytes,
but too much or too little genetic material halts development.
e.
A gamete including just one translocated chromosome will have too much of part
of the chromosome, and too little of other parts. Excess chromosome 21 material causes
Down syndrome.
7.
Patches of octaploid cells in liver tissue may arise as a result of abnormal mitosis in a few
liver cells early in development.
8.
a.
A XXX individual has no symptoms, but she may conceive sons with Klinefelter
syndrome by producing XX oocytes.
b.
A female with XO Turner syndrome has wide-set nipples, flaps of skin on the
neck, and no secondary sexual development.
c.
A female with trisomy 21 Down syndrome. Phenotype includes short, sparse,
straight hair, wide-set eyes with epicanthal folds, a broad nose, protruding tongue, mental
retardation, and increased risk of a heart defect, suppressed immunity, and leukemia.
9.
Basketball players may have an extra Y chromosome that makes them tall.
10.
trisomy = extra chromosome 18 in all cells mosaic = extra chromosome 18 in some cells
translocation = extra piece of 18 on a different chromosome
11.
Triploids are very severely abnormal. Trisomy 21 is the least severe trisomy, and
involves the smallest chromosome. Klinefelter syndrome symptoms are worse if there is more
than one extra X chromosome.
12.
A balanced translocation causes duplications or deletions when a gamete contains one
translocated chromosome, plus has extra or is missing genes from one of the chromosomes
involved in the translocation. A paracentric or pericentric inversion can cause duplications or
deletions if a crossover occurs between the inverted chromosome and its homolog.
Isochromosomes result from centromere splitting in the wrong plane, duplicating one
chromosome arm but deleting the other.
13.
Robertsonian translocation = 2 chromosomes join reciprocal translocation = 2
chromosomes exchange parts insertional translocation – part of one chromosome inserts into or
on another
14.
Chromosomes would not contort during meiosis because their genes are aligned.
15.
a.
FISH: Fluorescently-labeled DNA probes bind homologous regions on
chromosomes.
b.
Amniocentesis: Fetal cells and fluid are removed from around a fetus. Cells are
cultured and their chromosomes stained or exposed to DNA probes, and karyotyped.
c.
Chorionic villus sampling: Chromosomes in chorionic villus cells are directly
karyotyped.
d.
Fetal cell sorting: A fluorescence activated cell sorter separates fetal from
maternal cells, and fetal chromosomes are karyotyped.
16.
Trisomies 5 and 16 involve chromosomes with higher gene densities than 13 and 18.
Therefore, trisomies 5 and 16 stop development earlier and are less likely to be seen in
spontaneous abortions and births than trisomies 13 and 18.
17.
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18.
A female cannot have Klinefelter syndrome because she does not have a Y chromosome,
and a male cannot have Turner syndrome because he has a Y chromosome.
19.
Nondisjunction in oocyte. Nondisjunction in sperm. Large deletion in X chromosome.
Answers to Applied Questions
1.
A chromosome must include a centromere, telomeres, and origin of replication sites
2.
a.
Karen Martini
b.
The risks in the right hand column are higher because they include many
conditions.
c.
One in 66 is greater than 1 percent.
d.
Age 40 trisomy 21 risk = 1/106. Age 45 risk = 1/30. Her risk approximately
triples in the five years.
3.
The person is a girl missing part of the short arm of chromosome 5. This is cri du chat
syndrome, and she will be mentally retarded with a catlike cry.
4.
FISH
5.
a.
Reciprocal translocation
b.
She doesn't have extra or missing genes.
c.
She might have a child with translocation Down syndrome.
6.
At the second mitotic division, replicated chromosomes failed to separate, yielding one of
four cells with an extra two sets of chromosomes.
7.
Down syndrome caused by aneuploidy produces an extra chromosome 21 in each cell. In
mosaic Down syndrome, the extra chromosome is only in some cells. In translocation Down
syndrome, unbalanced gametes lead to an individual with extra chromosome 21 material in each
cell.
8.
The XXY son could have gotten two X chromosomes from his mother, or an XY-bearing
sperm from his father.
9.
a.
A translocation carrier can produce an unbalanced gamete that lacks chromosome
22 material.
b.
The microdeletion may be more extensive than the deleted region in the
translocation individuals.
c.
Translocation family members might be infertile or have offspring with birth
defects.
10.
a.
4 + 5, 9 + 10, 11 + 12 The lower chromosome # should have more bases.
b.
19
c.
Y
d.
6.2 times
11.
Band 13 of the short arm of chromosome 16
12.
mild trisomy 13 (Patau syndrome)
13.
an isochromosome
14.
a. it's lethal before birth
b. an inversion or an insertional translocation can lead to excess chromosome 16 material
15.
Many answers possible. Gorlin syndrome = basal cell nevus syndrome, OMIM 109400,
deletion in 9q, a form of skin cancer
16.
Student should create a karyotype.
17.
Chromosome 13:
cataract-clouded lens OMIM 601885
deafness
220290
leukemia/lymphoma—blood cancer 602221
ectodermal dysplasia—no hair
129500
or nails, dark skin
18.
a.
Uniparental disomy
b.
The first condition might arise from an oocyte that has two copies of the long arm
of chromosome 14 being fertilized by a sperm that lacks this segment. The situation
would be the reverse for the second condition.
c.
19.
A deletion mutation could remove the copy of the gene that is expressed.
One of the Watkins probably has a balanced translocation, because there is more than one
Down syndrome case. The two spontaneous abortions were the result of unbalanced gametes.
Their problems are likely to repeat with a predictable and high frequency, because the
translocated chromosome is in half of the carrier parents' gametes. In contrast, the Phelps' child
with Down syndrome is more likely the result of nondisjunction, which is unlikely to repeat. The
Phelps child has trisomy 21 Down syndrome; the Watkins' child may only have a partial extra
copy of chromosome 21.
20.
a. the short arm
b. when crossovers occur between inverted chromosomes parts are skipped
c. duplication
21.
The fetus should be okay because each parent has one of the chromosome abnormalities
and the parents are healthy.
A SECOND LOOK
1.
insertional
2. The father has the normal amount of chromosomal material.
3. Marcos could have inherited a normal 10 and a normal 17 from his dad, or both abnormal
chromosomes