Chapter 4 Practice Problems

Question 1

one diploid cell gives rise to four haploid cells

Answer 1

meiosis

Question 2

haploid germ cells that unite at fertilization

Answer 2

gametes

Question 3

the array of chromosomes in a given cell

Answer 3

karyotype

Question 4

one diploid cell gives rise to two diploid cells

Answer 4

mitosis

Question 5

the part of the cell cycle during which the chromosomes are not visible

Answer 5

interphase

Question 6

an animal cell containing more than one nucleus

Answer 6

syncytium

Question 7

pairing of homologous chromosomes

Answer 7

synapsis

Question 8

X and Y

Answer 8

sex chromosomes

Question 9

division of the cytoplasm

Answer 9

cytokinesis

Question 10

the time during mitosis when sister chromatids separate

Answer 10

anaphase

Question 11

one of the two identical halves of a replicated chromosome

Answer 11

chromatid

Question 12

chromosomes that do not differ between sexes

Answer 12

autosomes

Question 13

site of the closest connection between sister chromatids

Answer 13

centromere

Question 14

microtubule organizing centers at the spindle poles

Answer 14

centrosomes

Question 15

cell produced by meiosis that does not become a gamete

Answer 15

polar body

Question 16

cells in the testes that undergo meiosis

Answer 16

spermatocytes

Question 17

Humans have 46 chromosomes in each somatic cell.

a. how many chromosomes does a child receive from its father?
b. how many autosomes and how many sex chromosomes are present in each somatic cell?
c. how many chromosomes are present in a human ovum?
d. how many sex chromosomes are present in a human ovum?

Answer 17

a. 23 chromosomes
b. 44 autosomes and 2 sex chromosomes
c. 23 chromosomes
d. 1 sex chromosome

Question 18

Researchers discovered recently that the sole function of the SRY protein is to activate an autosomal gene called Sox9 in the presumptive gonad (before ir has decided to become. a testis or ovary)

a. what would be the sex of an XY individual homozygous for nonfunctional mutant alleles of Sox9? explain.
b. given your answer to part a why us SRY considered the male determining factor? (what would happen if you did in an experiment like the Fast Forward box?)

Answer 18

a. an XY individual who is homozygous for a nonfunctional mutant allele of Sox9 would develop as a female.
b. This XX mouse with a Sox9 transgene would develop as a female, not a male. The reason is that the Sox9 transgene could not be activated in the absence of the SRY protein.

Question 19

One oak tree cell with 14 chromosomes undergoes mitosis. How many daughter cells are formed, and what is the chromosome number in each cell?

Answer 19

2; 14

Question 20

Can you think of anything that would prevent mitosis from occurring in a cell whose genome is haploid?

Answer 20

no, mitosis occurs in haploid cells

Question 21

One oak tree cell with 14 chromosomes undergoes meiosis. How many cells will result from this process, and what is the chromosome number in each cell?

Answer 21

4; 7

Question 22

which type(s) of cell division reduces the chromosome number by half? Which types of cell division can be classified as reductional? which type of cell division is classified as equational?

Answer 22

meiosis 1; meiosis 1; meiosis 2 and mitosis

Question 23

Complete the following statements using as many of the following terms as are appropriate: mitosis, meiosis 1, meiosis 2, and none

a. the spindle apparatus is present in cells undergoing _____
b. chromosomes replication occurs just prior to _____
c. the cells resulting from ____ in a haploid cell have a policy of n
d. the cells resulting from ____ in a diploid cell have a policy of n
e. homologous chromosome pairing regularly occurs during ___
f. nonhomologous chromosome pairing regularly occurs during ____
g. physical recombination leading to the production of recombinant progeny classes occurs during ____
h. the separation of sister centromeres occurs during ___
i. non sister chromatids are found in the same cell duringg ____

Answer 23

a. mitosis, meiosis 1, meiosis 2
b. mitosis, meiosis 1
c. mitosis
d. meiosis 1, meiosis 2
e. meiosis 1
f. none
g. meiosis 1
h. meiosis 2, mitosis
i. mitosis, meiosis 1

Question 24

Assuming (i) that the two chromosomes in every homologous pair carry different alleles of some genes and (ii) that no crossing over takes place, how many genetically different offspring could any one human couple potentially produce? which of these two assumption sis more realistic?

Answer 24

Using the assumptions given, each person can produce 223 genetically different gametes. Thus, the couple could potentially produce 223 × 223 = 246 or 70,368,744,177,664 different zygotic combinations. That is 70 trillion, 368 billion, 744 million, 177 thousand, 664 genetically different children.
It is very realistic to assume that homologous chromosomes carry different alleles of some genes. As we will see later in the book, there are about 3 million differences between the DNA sequences in the two haploid human genomes in any one
human being, or on average about 130,000 differences between any two homologous chromosomes. In contrast, crossing-over almost always occurs between homologous chromosomes in any meiosis; you will remember that crossing-over is needed to allow the homologous chromosomes to segregate properly during meiosis I. Thus, the second assumption is much less realistic.

Question 25

In the moss Polytrichum Commune, the haploid chromosome number is 7. A haploid male gamete fuses with a haploid female gamete to form a diploid cell that divides and develops into the multicellular sporophyte. Cells of the sporophyte then undergo meiosis to produce haploid cells called spores. what is the probability that an individual spore will contain a set of chromosomes all of which came from the male gamete?

Answer 25

The diploid sporophyte contains 7 homologous pairs of chromosomes. One chromosome in each pair came from the male gamete and the other from the female gamete. When the diploid cell undergoes meiosis one homolog of each pair ends up in the gamete. For each homologous pair, the probability that the gamete contains the homolog inherited from the father = 1/2. The probability that a gamete contains only the homologs inherited from the father is (1/2)7 = 0.78%.

Question 26

can you think of anything that would prevent meiosis from occurring in an organism whose genome is always haploid?

Answer 26

Yes. Meiosis requires the pairing of homologous chromosomes during meiosis I, so meiosis cannot occur in a haploid organism

Question 27

The pseudoautosomal regions of the X and Y chromosomes enable the sex chromosomes to pair and synapse during meiosis in males. Given the location of the SRY gene near PAR1, can you propose a mechanism for how the mutant x and Y chromosomes may have arisen during meiosis?

Answer 27

some kind of crossing-over event occurred between a normal X chromosome and a normal Y chromosome.

Question 28

In humans: a. How many sperm develop from 100 primary spermatocytes? b. how many sperm develop from 100 secondary spermatocytes c. how many sperm develop from 100 spermatids d. how many ova develop from 100 oocytes e. how many ova develop from 100 secondary oocytes f. how many ova develop from 100 polar bodies

Answer 28

a. 400 sperm b. 200 sperm c. 100 sperm d. 100 ova e. 100 ova f. no ova

Question 29

In Drosophila, the autosomal recessive brown eye color mutation displays interactions with both the x linked recessive vermilion mutation and the autosomal recessive scarlet mutation. Flies homozygous for brown and simultaneously hemizygous or homozygous for vermilion have white eyes. Flies simultaneously homozygous for both the brown and scarlet mutations also have white eyes. Predict the F1 and F2 progeny of crossing the following true breeding parents a. vermilion females x brown males b. brown females x vermilion males c. scarlet females x brown males d. brown females x scarlet males

Answer 29

a. ); the ratio for both genes in both F2 females and males = 3/8 v+ bw+– (wild type) : 3/8 v bw+ (vermilion) : 1/8 v+ bw bw (brown) : 1/8 v bw bw (white). b. F2 males is 3/8 v+Y bw+– (wild type) : 3/8 vY bw+– (vermilion) : 1/8 v+Y bw bw (brown) : 1/8 vY bw bw (white).F2 females is 3/4 v+– bw+– (wild type) : 1/4 v+– bw bw (brown) c. The F2 dihybrid ratio (which hold for both sexes) = 9/16 st+– bw+– (wild type) : 3/16 st+– bw bw (brown) : 3/16 st st bw+– (scarlet) : 1/16 st st bw bw (white). d. F1 bw+bw st+st (wild type) → F2 as in part (c) above.

Question 30

Duchenne muscular dystrophy is caused by a relatively rare x linked recessive allele. it results in progressive muscular wasting and usually leads to death before age 20. In this problem, an affected person is one with the severe form of DMD caused by hemizygosity or homozygosity for the disease allele. a. what is the probability that the first son of a woman whose brother is affected will be affected. b. what is the probability that the second son of a woman whose brother is affected will be affected, if her son was affected c. what is the probability that a child of an unaffected man whose brother is affected will be affected? d. an affected man mates with his unaffected first cousin; there is otherwise no history of DMD in this family, if the mothers of this man and his mate were sisters, what is the probability that the couple's first child will be an affected boy? an affected girl? an unaffected child? e. if the two related parents of the couple in part d were brother ad sister what is the probability that the couples first child will be an affect boy?an affect girl? an unaffected child?

Answer 30

``` a. 1/4 b, 1/2 c.no chance d. 1/2; 1/6; 7/8 e. 0; 0; 100 f.0; 0; 100% ```

Question 31

the x linked gene responsible for DND encodes a protein called dystrophin that is required for muscle function. Dystrophin protein is not secreted - it remains in the cells that produce it. Given what you know about Barr body formation, do you think that females heterozygous for the recessive DMD disease allele could have the disease in some parts of their bodies and not others?

Answer 31

Yes, it is possible that a woman heterozygous for the disease-causing allele of the DMD gene could have symptoms in some parts of the body and not others.

Question 32

Men have hemophilia when they are homozygous for a nonfunctional recessive mutant allele of the x linked gene for clotting factor VIII. Factor VIII is normally secreted into the blood serum by cells in the bone marrow that produce it. a. do you think that females heterozygous for the hemophilia disease allele could have hemophilia in some parts of their bodies and not others? b. if such a female carrier of hemophelia suffered a cut, would her blood coagulate faster, slower, or in about the same time as that of an individual homozygous for a normal allele of the factor VIII gene? would the rate of clotting vary significantly among heterozygous females?

Answer 32

a. it is very unlikely that females heterozygous for the hemophilia disease allele would have the condition in some parts of the body but not others. b. It is conceivable that the rate of clotting may vary considerably among heterozygous women,

Question 33

In the fast forward box, suppose the investigators had looked at the expression of green and red fluorescent protein in early mouse embryos, when the embryos have fewer than 500 cells. what patterns would they likely have observed?

Answer 33

all of the cells express the genes on both X chromosomes, including both the GFP and RFP transgenes. Cells that express both GFP (green) and RFP (red) appear fluorescent yellow.