Genetics--Homework Question #2

According to Chargoff's rule what is the % of A, G, C, and T to each other?

%A+%G=%T+%C %A=%T %G=%C

Patients who have a defect in one of the DNA repair systems may have what?

-increased number of skin lesions, such as freckles -increased chance of cancer

In a segment of DNA, an A base is changed to a C and the error is copied during replication. Under which circumstances is that change considered a mutation?

-the change alters the phenotype of the organism's offspring -the change results in production of a novel protein -the change is in a somatic cell, such as a skin cell -the change is in a gene, but has no effect on a gene product or phenotype

A region of DNA has six copies of a trinucleotide repeat. During one round of replication, the template strand slips as shown in the diagram. How many repeats will the DNA have if the newly synthesized strand is used as a template in the next round of replication?

4

One nonhistone protein that acts as an enzyme is____________, which is crucial to replication.

DNA polymerase

If any of these examples of DNA damage are not repaired before __________, the information content of DNA is changed __________.

DNA replication; permanently

The FISH technique utilizes ________ hybridization to identify the presence and location of specific DNA sequences in chromosomes.

DNA-DNA

_______ is the removal of an amino group. Deamination of C to form U followed by DNA replication may result in a _______ to ______ transition.

Deamination

______ occurs when an A or G base is excised from the DNA, leaving behind a site with no base. DNA polymerase will introduce a ______ base opposite the apurinic site.

Depurination; random

G bands are so named because of the use of the ______, which darkens certain regions of the chromosome.

Giemsa stain

Researcher who performed experiments in bacterial transformation:

Griffith

What is the role of H1 in a nucleosome?

H1 histone associates with DNA as it enters and leaves the nucleosome

A model structure formed during DNA crossover between nonsister chromatids

Holliday junction

This loop then base pairs with the non-invading 3' tail, and new DNA synthesis fills in the gaps, forming two X-shaped __________.

Holliday junctions

Which of the following are involved in repair of DNA with thymine dimers? I. The enzyme photolyase II. Exposure to light III. Capture of energy to split the dimers

I, II, and III

How many base pairs is the linker DNA that connects one end of a nucleosome to the next?

40 base pairs

If E. coli cells containing 15N15N (heavy) DNA are grown for TWO generations in 14N medium, the cells will contain______.

50% 15N14N and 50% 14N14N DNA

A region of DNA has six copies of a trinucleotide repeat. During one round of replication, the newly synthesized strand slips as shown in the diagram. If the loop is not repaired (cut out), how many repeats will be present in DNA if this newly synthesized strand is used as a template in the next round of replication?

8

Researcher who performed experiments that demonstrated semiconservative replication:

Messelson and Stahl

Homologous recombination occurs in a heterozygote in which alleles D and d differ by a single base pair. The D allele has a G at one position, whereas the d allele has a C at the same position. If branch migration causes heteroduplex formation across this position, what is the expected outcome?

Mismatch repair will identify an abnormal G:G base pair and may convert the D allele to a d allele

____________ proteins are a broad category that includes hundreds to thousands of different proteins with a variety of functions.

Nonhistone proteins

A single-stranded molecule with a free 3' hydroxyl group to which DNA polymerase can attach free dNTPs:

RNA primer

Two strains of S. cerevisae (yeast) are crossed. One has the genotype A B and the other a b. Which statement correctly describes the tetrads that can be produced by one reciprocal exchange between the A and B genes without gene conversion in the dihybrid?

Recombination occur at the four-strand stage to produce a tetrad with AB, Ab, aB, and ab chromosomes

The normal functions of Spo11 and Cas9 enzymes are different because

Spo11 produces double-strand breaks in many genomic locations during meiosis, whereas Cas 9 is targeted to specific sequences by a CRISPR RNA

If a cell had a single nonfunctional DNA repair enzyme, how would that cell be affected?

The cell's other DNA repair enzymes would most likely compensate and cell viability would be maintained

________ is chromosomal regions that remain condensed at most times in all cells; for example, most of the Y chromosome in humans.

constitutive heterochromatin

Naturally occurring radiation, such as _______, can break the sugar-phosphate backbone and lead to ______ of DNA bases.

cosmic rays and X-rays; deletion

UV light damages DNA by causing:

covalent bonds to form between thymine bases next to each other on the same DNA strand

The information stored in DNA can change by natural processes that ______ DNA.

damage

G bands (do/do not) indicate differences in base composition.

do not

During meiotic prophase, a ___________ is made in one of the chromatids of one homolog.

double-strand break

Suppose you had a strain of cells that lacked functional CENP-A histone protein. What would be the result of this?

during mitosis, the centromeres would not migrate properly to the opposite poles

Telomerase contains______. a. different RNA molecules b. a DNA molecule c. both DNA and RNA molecules d. different DNA molecules e. an RNA molecule

e. an RNA molecule

How does the antiparallel polarity of DNA strands contribute most to the integrity of genetic information?

each antiparallel strand can serve as a template to produce the other stand in the event of DNA damage

______ is a chromosomal region that does not stain as darkly when treated with DNA-binding chemicals; it is less condensed.

euchromatin

___________ are regions of chromosomes (or even whole chromosomes) that are heterochromatic in some cells and euchromatic in other cells of the same organism.

facultative heterochromatin

True or false: Only pyrimidine dimers are repaired by nucleotide excision repair.

false

true or false: a single point mutation can affect many genes

false

true or false: more point mutations are found in human eggs than in sperm

false

true or false: the rate of reverse mutations is higher than the rate of forward mutation

false

true or false: DNA reaches maximum compaction during prophase

false

true or false: condensins decondense chromosomes after mitosis

false

true or false: formation of loops is thought to result in a fiber about 100 A wide

false

true or false: in a nucleosome, DNA wraps in a smooth coil around the core histones

false

true or false: investigators have a complete understanding of the features of higher-order chromosome packaging

false

true or false: mutations in somatic cells can be inherited by the progeny

false

True or false: Meselson and Stahl performed the density-gradient centrifugation of DNA in a solution of calcium chloride.

false; it was cesium chloride

______ is a chromosomal region that stains darkly when treated with DNA-binding chemicals; it is more condensed.

heterochromatin

The region between these two junctions is termed the __________ region. This region is enlarged by ______________ as the junctions move outward in a zipper-like fashion.

heteroduplex; branch migration

Cohesin complexes_______.

hold a chromosome's sister chromatids together

High-resolution banding produces (hundreds/thousands) of bands on chromosomes in a human karyotype.

hundreds

The pattern of bands can be shown in an _________ to indicate locations of genes.

idiogram

The five types of histone proteins contain a preponderance of the basic, positively charged amino acids ______ and _______, which help neutralize and stabilize the negatively charged DNA double helix.

lysine and arginine

A karyotype is a set of fully compacted chromosomes from a cell at ________.

metaphase

One of the tails invades the nearby double strand of the _________. The invading strand base pairs with one of the two strands, and the displaced strand forms a _________.

nonsister chromatid; D-loop

Four histones associate to form the core of the_______.

nucleosome

Short DNA fragments formed by discontinuous replication of one of the strands:

okazaki fragments

The Meselson-Stahl experiment demonstrated that DNA replication produces two DNA molecules each composed of____.

one old and one new strand

A short sequence of bases at which unwinding of the double helix for replication begins:

origin

The short arm of a chromosome is termed the ___ arm, while the long arm is the ____ arm.

p arm; q arm

The linkages between the components of a single nucleotide are arranged as

phosphate-sugar-base

___________ is a phenomenon that occurs when a gene is moved close to a heterochromatic region, such that its expression ceases.

position-effect variegation (PEV)

A nitrogenous base containing a double ring is a:

purine

A nitrogenous base containing a single ring is a:

pyrimidine

The first step in base excision repair is:

recognizing and excising the incorrect base from a nucleotide within DNA

The pattern of G-banding seen in particular chromosome is (stable/unstable) across generations.

stable

During meiotic prophase in a eukaryotic cell, Spo11 initiates recombination by causing a double-strand break in DNA between Gene A and Gene B on one sister chromatid. Which of these events will occur prior to formation of a Holliday junction?

strand invasion causes one strand of the uncut chromatid to form a D loop

A structure at the end of a eukaryotic chromosome:

telomere

Suppose a mutation in separase allows it to recognize but not cleave cohesin. What is the most likely outcome for cells expressing this form of separase?

the cells would have a high rate of chromosome segregation errors

In light repair, ______.

the covalent bonds between the thymine dimers are broken

What characteristic of DNA molecules makes it require higher temperatures to denature?

the more G and C bases, the higher the temp for denaturation to occur

Ultraviolet light, which produces ________, and oxidation also damage DNA.

thymine dimers

What protein prevents supercoiling of the DNA strands ahead of the replication bubble?

topoisomerase

Chromosomal changes detectable through SKY karyotyping include deletions, insertions, duplications, inversions, and________.

translocations

True or false: Following base removal, DNA polymerase can add nucleotides in the 5'-to-3' direction.

true

True or false: packaging into nuclesomes condenses DNA approxiamtely 7-fold

true

true or false: Chemical agents can cause mutations by ethylating guanine residues in DNA.

true

true or false: DNA mutations are passed on to a cell's progeny

true

true or false: Improper base-pairing during DNA replication causes a pause in chain elongation.

true

true or false: The addition of a single base pair to the coding region of a gene can cause a frameshift mutation:

true

true or false: a deletion is the loss of a block of one or more nucleotide pairs from a DNA molecule

true

true or false: a forward mutation changes a wild-type allele to a different allele

true

true or false: a substitution is the replacement of one DNA base with another

true

true or false: mendel studied the inheritance of germ line mutations in pea plants

true

true or false: only a small subset of mutations affect gene function

true

true or false: the mutation rate of a gene depends on a gene size

true

true or false: DNA reaches maximum compaction during metaphase

true

true or false: DNA wrapped around core histones in a nucleosome exhibits sharp bends as well as unbent regions

true

true or false: condensins form chromatin loops attached to the scaffold

true

true or false: formation of chromatin loops results in DNA supercoiling that is replaced by DNA topoisomerase II

true

How many base pairs wrap twice around the octameric core?

160 base pairs

In resection, the 5' ends at the break are degraded, leaving two _________.

3' single stranded tails

DNA polymerases use their ________ activity to remove a mismatched base.

3' to 5' exonuclease

What is the correct order of these events in recombination that is resolved by the crossover pathway? 1. Double-strand break formation 2. Strand invasion 3. Resection 4. Resolution of the double Holliday junction 5. Branch migration 6. Formation of a double Holliday junction

1, 3, 2, 6, 5, 4

What are the four steps of separation of sister chromatids during mitosis?

1. As the cell enters the S phase, each chromosome begins not only replication of its DNA but also production of histone and nonhistone proteins. (This occurs before condensation.) 2. The arms and centromeres of the replicated sister chromatids are held together by cohesin. 3. Cohesin is cleaved by the time cells leave metaphase. 4. The cohesin holding together the centromeres of the sister chromatids is cleaved, and the chromatids are moved to opposite poles.

What are the four steps of the replica plating technique?

1. Bacterial colonies are grown on a master plate that does not contain penicillin. The master plate is inverted onto the velvet. Some cells from each colony remain on the velvet. The master plate is saved. 2. A test plate containing penicillin is inverted onto the velvet. It picks up bacteria in a pattern that is a replica of the master plate. 3. The replica plate is incubated to allow the transferred bacterial cells to form colonies. 4. Only penicillin-resistant cells grow and form colonies. The position of resistant colonies on the master plate is inferred by comparison with the test plate.

What are the steps of base excision repair?

1. One strand of the DNA contains a deaminated base, such as uracil. 2. A uracil-specific DNA glycosylase recognizes and removes the uracil, leaving an apyrimidinic (AP) site. 3. AP endonuclease nicks the DNA backbone at the AP site. 4. DNA exonuclease removes nucleotides near the nick, leaving a gap. 5. DNA polymerase synthesizes new DNA to fill the gap. 6. DNA ligase seals the nick in the backbone.

Chromatin is a complex of DNA and protein; roughly ______is DNA, and _____is evenly divided between histone and nonhistone proteins.

1/3 is DNA and 2/3 is evenly divided between histone and nonhistone proteins

In mammals, the inactivated X chromosome in each cell that is completely heterochromatic and thus densely staining. This is called_____

Barr body

What part of a T2 bacteriophage enters a bacterial cell following infection?

DNA

DNA in a chromosome consists of ____.

a single linear molecule

This chemical modification to histone tails is associated with open chromatin. This is _______.

acetylation

Which of the following is required to replicate the lagging strand of DNA? a. primase b. okazaki fragments c. DNA ligase d. all of the above

all of the above

Which of the following are characteristics of telomerase: a. contains a DNA molecule complementary to telomere repeats b. contains an RNA molecule complementary to telomere repeats c. functions as an enzyme d. expressed in all somatic cells e. expressed in germ cells

b, c, e

A bacteria that infects bacteria is called:

bacteriophage

Deletion of a nucleotide in a protein-coding region during DNA replication causes_____.

causes the amino acid sequence encoded after the deletion to be incorrect.

A _________ is the point at which spindle fibers attach during cell division; it is flanked by regions of heterochromatin.

centromere

Noncoding, repetitive DNA is found in ________________ of chromosomes; these structures play important roles during replication.

centromeres and telomeres