Chapter 15 & 16 Study Questions

If a DNA sample were composed of 10% thymine, what would be the percentage of guanine?

40%

What would be the sequence of the DNA molecule made by replication of the DNA molecule shown below?5' TTCCGGA 3'

5' TCCGGAA 3'

A space probe returns with a culture of a microorganism found on a distant planet. Analysis shows that it is a carbon-based life-form that has DNA. You grow the cells in 15N medium for several generations and then transfer them to 14N medium and grown them for another generation. Which pattern in the figure shown below would you expect if the DNA was replicated in a conservative manner?

B

Recombination between linked genes comes about for what reason?

Crossovers between these genes result in chromosomal exchange.

Which of the following shows the correct base pairing of deoxyribonucleotides that occurs in nature?

G and C

How do some scientists feel that telomerase might be used to slow the aging process?

If telomerase activity was increased in our cells, the rate at which our chromosomes shorten as we age might be decreased

_____ is usually less severe than _____, and _____ species have been observed in plants, fish, amphibians, and even mammals.

Polyploidy ... aneuploidy ... polyploid

What is "chromatin"?

The combination of DNA and proteins that forms chromosomes

Map units on a linkage map cannot be relied upon to calculate physical distances on a chromosome for which of the following reasons?

The frequency of crossing over varies along the length of the chromosome.

A chromosome is

a single long DNA molecule plus the proteins with which that DNA molecule is complexed

The pairs of nucleotides that interact to join together two DNA strands are known as

complementary nucleotides

The reaction used to join together nucleotides to form a nucleotide chain is known as a

dehydration reaction

Which of the following enzymes covalently connects segments of DNA?

ligase

The covalent linkages joining together nucleotides in a DNA molecule are known as

phosphodiester linkages

Telomeres are

the ends of linear chromosomes

"X inactivation" refers to

the inactivation of most of the genes on one X chromosome in genetic females

If two genes are linked, _____.

they are on the same chromosome

What is the function of DNA polymerase III?

to add nucleotides to the 3' end of a growing DNA strand

What is the probability that a male will inherit an X-linked recessive allele from his father?

0%

Between which two genes would you expect the highest frequency of recombination?

A and G

A woman is red-green color-blind. What can we conclude, if anything, about her father?

He is red-green color-blind.

Which of the following statements about histones is FALSE?

Histones help transport mRNA molecules out of the nucleus

Which of the following statements describes the eukaryotic chromosome?

It consists of a single linear molecule of double-stranded DNA plus proteins.

In humans, which chromosome combinations normally determine whether an individual is biologically female or male?

XX individuals are biologically female, XY individuals are biologically male

If an organism uses the "conservative" model of DNA replication, rather than the normal "semi-conservative" model of DNA replication,

after DNA replication occurs, one of the two double-stranded DNA molecules will consist of two "daughter" DNA strands and the other will consist of two "parental" DNA strands

Which of the following would result in genetic variation by way of new combinations of alleles?

all of these answers are correct

A "Barr body" is

an inactive X chromosome

Cells that have a number of chromosomes different from the normal number for their species are known as _____.

aneuploid

In a nucleosome, the DNA is wrapped around

histones

Males are more often affected by sex-linked traits than females because

males only have one copy of the X chromosome.

The ends of linear chromosomes are known as

telomeres

A woman is a carrier for red-green color blindness, a sex-linked trait. Her husband is normal (not color-blind) for this trait. What are the chances that their newborn daughter will be red-green color-blind?

0%

The centimorgan (cM) is a unit named in honor of Thomas Hunt Morgan. To what is it equal?

1% frequency of recombination between two genes

Cinnabar eyes is a sex-linked recessive characteristic in fruit flies. If a female having cinnabar eyes is crossed with a wild-type male, what percentage of the F1 males will have cinnabar eyes?

100%

Cytosine makes up 38% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

12

At a specific area of a chromosome, the sequence of nucleotides below is present where the chain opens to form a replication fork:3' C C T A G G C T G C A A T C C 5'An RNA primer is formed starting at the underlined T (T) of the template. Which of the following represents the primer sequence?

5' A C G U U A G G 3'

What would be the sequence of the DNA molecule made by replication of the DNA molecule shown below?5' AAGGCTT 3'

5' AAGCCTT 3'

An Okazaki fragment has which of the following arrangements?

5' RNA nucleotides, DNA nucleotides 3'

What would be the sequence of the DNA molecule made by replication of the DNA molecule shown below?5' GCGAATA 3'

5' TATTCGC 3'

Hemophilia is a sex-linked disorder. The daughter of a father with hemophilia and a carrier mother has a _____ probability of having hemophilia.

50%

In werewolves (hypothetically), pointy ears (P) are dominant over round ears (p). The gene is on the X chromosome. (Sex determination in werewolves is the same as for "other" humans.) A certain female werewolf has pointy ears even though her father had round ears. What percentage of her sons will have round ears if she mates with a werewolf with round ears?

50%

In humans, male-pattern baldness is controlled by an autosomal gene (= a gene that is found on a chromosome other than an X or Y chromosome) that occurs in two allelic forms. Allele Hn determines nonbaldness, and allele Hb determines pattern baldness. In males, because of the presence of testosterone, allele Hb is dominant over Hn. If a man and woman both with genotype HnHb have a son, what is the chance that he will eventually be bald?

75%

Cytosine makes up 42% of the nucleotides in a sample of DNA from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

8%

Which of the following shows the correct base pairing of deoxyribonucleotides that occurs in nature?

A with T

Four genes (A, B, C, and D) are on the same chromosome. The recombination frequencies are as follows: A-B: 19%; B-C: 14%; A-C: 5%; B-D: 2%; A-D: 21%; C-D: 16%. Based on this information, which sequence of genes is correct?

ACBD

Why do our chromosomes become shorter as we age?

Because DNA polymerases can only add nucleotides to an existing nucleotide chain, an RNA primer is used to initiate DNA synthesis. Once that RNA primer is removed from the end of a linear chromosome, there is no mechanism to completely fill in the missing nucleotides at the end of a linear chromosome.

In the late 1950s, Meselson and Stahl grew bacteria in a medium containing "heavy" nitrogen (15N) and then transferred them to a medium containing 14N. Which of the results in the figure shown below would be expected after one round of DNA replication in the presence of 14N?

D

The process by which DNA molecules are copied so that when cells divide each cell can have a complete copy of the DNA is known as

DNA Replication

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base?

DNA in both daughter cells would be radioactive.

A biochemist isolates, purifies, and combines in a test tube a variety of molecules needed for DNA replication. When she adds some DNA to the mixture, replication occurs, but each DNA molecule consists of a normal strand paired with numerous segments of DNA a few hundred nucleotides long. What has she probably left out of the mixture?

DNA ligase

Which of the following enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of DNA fragments resulting from DNA replication of one of the two DNA strands?

DNA polymerase I

Which enzyme catalyzes the elongation of a DNA strand in the 5' → 3' direction?

DNA polymerase III

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?

DNA polymerase can join new nucleotides only to the 3' end of a growing strand.

A new DNA strand elongates only in the 5' to 3' direction because

DNA polymerase can only add nucleotides to the free 3' end.

Why are primases necessary in order for DNA replication to occur?

DNA polymerases can not initiate synthesis of new nucleotide chains

Sturtevant provided genetic evidence for the existence of four pairs of chromosomes in Drosophila in which of these ways?

Drosophila genes cluster into four distinct groups of linked genes.

E. coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. Which of the samples shown in the figure below shows the density distribution of DNA you would expect in this experiment?

E

Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?

Extra copies of the other chromosomes are probably fatal to the developing embryo.

Will the chromosomes you pass onto your children be shorter than your chromosomes?

Hopefully not, because telomerase will restore the telomeres in your germline cells (the cells that produce egg or sperm cells) to approximately their original length.

What happens to the short RNA "primers" that primase synthesizes and that are extended by DNA polymerase III during DNA replication?

In E. coli, DNA polymerase I removes the RNA primers and fills in the resulting gaps with deoxyribonucleotides

What is the role of DNA ligase during DNA replication?

It joins DNA fragments together.

Why are there concerns about using increased telomerase activity to slow down the aging process?

One concern is that increasing telomerase activity could increase cancer rates.

X-linked genes differ from Y-linked genes in which of the following ways?

Sons and daughters have equal probabilities in inheriting a recessive allele of an X-linked gene from their mother, but only sons can inherit rare Y-linked genetic disorders from their father.

Why do some scientists feel that telomerase might be used to slow the aging process?

Telomere extension in mice and worms has reversed some signs of aging.

What is meant by the description "antiparallel" regarding the strands that make up DNA?

The 5' to 3' direction of one strand runs counter to the 5' to 3' direction of the other strand.

Which of the following best describes the function of the XIST gene in X chromosome inactivation?

The XIST gene on the X chromosome to be inactivated is expressed to produce multiple RNA transcripts that bind to that chromosome and effectively cover it up, thereby generating a Barr body.

Which of the following statements is true of linkage?

The closer two genes are on a chromosome, the lower the probability that a crossover will occur between them.

A red-eyed female fly was crossed with a white-eyed male fly. All the F1 offspring had red eyes. Two of these red-eyed F1 generation flies were crossed to each other. The F2 generation included both red- and white-eyed flies. Remarkably, all the white-eyed flies were male. What was the explanation for this result?

The gene involved is on the X chromosome.

How would one explain a testcross involving F1 dihybrid flies in which more parental-type offspring than recombinant-type offspring are produced?

The two genes are closely linked on the same chromosome.

What does a frequency of recombination of 50% indicate?

The two genes are likely to be located on different chromosomes.

In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (3H thymidine) for several minutes and then switched to nonradioactive medium. It is then viewed by electron microscopy and autoradiography. The figure shown below represents the results.The grains in the figure represent radioactive material within the replicating eye.Which of the following is the most likely interpretation?

There are two replication forks going in opposite directions.

What is the reason that linked genes are inherited together?

They are located close together on the same chromosome.

Duchenne muscular dystrophy is caused by a sex-linked recessive allele. Its victims are almost invariably boys, who usually die before the age of 20. Why is this disorder almost never seen in girls?

To express an X-linked recessive allele, a female must have two copies of the allele.

Which of the following shows the correct base pairing of ribonucleotides that occurs in nature?

U with A

A genetic defect in humans results in the absence of sweat glands in the skin. Some men have this defect all over their bodies, but in women it is usually expressed in a peculiar way: A woman with this defect typically has small patches of skin with sweat glands and other patches without sweat glands. In women, the pattern of sweat-gland distribution can best be explained by _____.

X chromosome inactivation

Red-green color blindness is a sex-linked recessive trait in humans. Two people with normal color vision have a color-blind son. What are the genotypes of the parents?

XCXc and XCY

Which of the following will happen to your chromosomes as you become older?

Your chromosomes will become shorter.

Which of the following would you expect of a eukaryote lacking telomerase?

a reduction in chromosome length in gametes

According to the "semi-conservative" model of DNA replication,

after DNA replication occurs, each of the two double-stranded DNA molecules will consist of one "daughter" and one "parental" DNA strand

When a DNA molecule is replicated,

all of these answers are correct

Which of the following statements regarding DNA polymerases is TRUE?

all of these statements are true

Which of the following statements regarding primases is TRUE?

all of these statements are true

The chromosome theory of inheritance states that _____.

all these answers are correct

Which of the following are NOT components of a nucleotide?

an "R" group

In Klinefelter syndrome, individuals are phenotypically male, but they have reduced sperm production and may have some breast development in adolescence. The cells of Klinefelter individuals have two X chromosomes and one Y (they are XXY instead of XY). This occurs because of what meiotic error?

aneuploidy

When a person has Down syndrome, he or she has an extra chromosome 21. Therefore, Down syndrome is a kind of _____ and results from _____.

aneuploidy ... nondisjunction of chromosome 21 during meiosis I

Histones are

art of nucleosomes

In a series of mapping experiments, the recombination frequencies for four different linked genes of Drosophila were determined as shown in the figure below. What is the order of these genes on a chromosome map?

b-rb-cn-vg

The formation of hydrogen bonds between complementary nucleotides is known as

base pairing

The elongation of the leading strand during DNA synthesis

depends on the action of DNA polymerase.

According to the "semi-conservative" model of DNA replication, after a double-stranded DNA molecule is replicated

each of the two resulting double-stranded DNA molecules will consist of one "daughter" and one "parental" DNA strand

Inactivation of one of the two X chromosomes in females occurs early during embryo development. A random X chromosome is inactivated in each cell present during the period during which inactivation occurs. As a consequence

females are a mosaic of two types of cell, those with the active X chromosome derived from the father and those with the active X chromosome derived from the mother.

A "sex-linked" gene is a

gene found on either the X or Y chromosomes

The recombination frequency between two gene loci is _____.

greater as the distance between the two loci increases

What kind of chemical bond is found between paired bases of the DNA double helix?

hydrogen

The two strands of a double-stranded DNA molecule are held together by

hydrogen bonds

The two strands of a double-stranded DNA molecule are held together by

hydrogen bonds between complementary nitrogenous bases

In a double-stranded DNA molecule, the two DNA strands base pair in such a way that the 5' end of one DNA strand base pairs with the 3' end of the other DNA strand. The two DNA strands are said to be

in an antiparallel arrangement

You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). These two classes of DNA probably represent

leading strands and Okazaki fragments.

"Linked genes" are

located near each other on the same chromosome and thus tend to be inherited together

Because the frequency of crossing over is not uniform along the length of a chromosome, _____.

map units do not necessarily correlate to physical distances along the chromosome

Women (and all female mammals) have one active X chromosome per cell instead of two. What causes this?

modification of the XIST gene so that it is active only on one X chromosome, which then becomes inactive

During meiosis, homologous chromosomes sometimes "stick together" and do not separate properly. This phenomenon is known as _____.

nondisjunction

DNA polymerases can add deoxyribonucleotides to

only the 3' end of an existing nucleotide chain

DNA replication begins are special sites on the parental DNA molecule known as

origins of replication

Which of the following enzymes initiates the synthesis of a new nucleotide chain during DNA replication?

primase

Which of the following enzymes synthesizes short segments of RNA?

primase

Histones are

proteins around which the DNA in chromosomes wrap

Which of the following describes the sequence of events that occurs during DNA replication of a double-stranded DNA molecule?

separation of the DNA strands at DNA replication origins, unwinding of the DNA double helix, synthesis of RNA primers, synthesis of DNA, ligation of DNA fragments

The DNA molecule is able to carry a vast amount of hereditary information in which of the following?

sequence of bases

The leading and the lagging strands differ in that

the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.

Wild type refers to _____.

the most common phenotype thought to be found in the natural population

In an X-linked, or sex-linked, trait, it is the contribution of _____ that determines whether a son will display the trait.

the mother

The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that

the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose.

How do the nucleotides used to make RNA molecules differ from those used to make DNA molecules?

the nucleotides used to make RNA molecules have ribose instead of deoxyribose as their sugar and uracil instead of thymine as one of their nitrogenous bases

In cats, black fur color is caused by an X-linked allele; the other allele at this locus causes orange color. The heterozygote is tortoiseshell. What kinds of offspring would you expect from the cross of a black female and an orange male?

tortoiseshell females; black males