Homework questions Final exam Ch.11-14

Which of the following statements correctly describes aneuploid conditions?

Monosomy X is the only known viable human monosomy.

Part complete If cell X enters meiosis, and nondisjunction of one chromosome occurs in one of its daughter cells during meiosis II, what will be the result at the completion of meiosis?

One-fourth of the gametes descended from cell X will be n + 1, 1/4 will be n - 1, and 1/2 will be n.

Chapter 13: What is meant by the description "antiparallel" regarding the two strands of nucleic acids that make up DNA?

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

Duchenne muscular dystrophy is a serious condition caused by a recessive allele of a gene on the human X chromosome. The patients have muscles that weaken over time because they have absent or decreased dystrophin, a muscle protein. They rarely live past their 20s. How likely is it for a woman to have this condition?

Very rarely: it is rare that an affected male would mate with a carrier female.

In the 1920s, Hermann Muller discovered that X-rays caused genetic changes in Drosophila. In a related series of experiments in the 1940s, other scientists discovered that other types of chemicals have a similar effect. A new chemical food additive is developed by a cereal manufacturer. Why is it necessary to test for its ability to cause mutation?

We want to prevent any chance that it might cause mutations

Tables like the one shown here are useful for organizing sets of data representing a common set of values (in this case, percentages of A, G, C, and T) for a number of different samples (in this case, species). Data from several papers by Chargaff: for example, E. Chargaff et al., Composition of the desoxypentose nucleic acids of four genera of sea-urchin, Journal of Biological Chemistry 195: 155-160 (1952).

Yes, because the %A approximately equals the %T and the %G approximately equals the %C in both species.

Assume that you are trying to insert a gene into a plasmid. Someone gives you a preparation of genomic DNA that has been cut with restriction enzyme X. The gene you wish to insert has sites on both ends for cutting by restriction enzyme Y. You have a plasmid with a single site for Y, but not for X. Your strategy should be to

cut the DNA again with restriction enzyme Y and insert these fragments into the plasmid cut with the same enzyme.

Which of the following statements describes the major reason that the individual with the genotype AaBbCCDdEE can make many kinds of gametes?

different possible assortment of chromosomes into gametes

Which of the following sets of materials is required by both eukaryotes and prokaryotes for DNA replication?

double-stranded DNA, four kinds of DNA nucleotides, primers, origins of replication

Part complete Refer to the following information to answer the questions below. A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive. What proportion of their sons would be color-blind and of normal height?

half

A woman is found to have 47 chromosomes, including three X chromosomes. Which of the following describes her expected phenotype?

healthy female of slightly above-average height

Part complete During DNA replication, which of the following enzymes separates the DNA strands during replication?

helicase

The "universal" genetic code is now known to have exceptions. Evidence for this can be found if which of the following is true?

if UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only)

Part complete The following information should be used for the next few questions. A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The charged transfer RNA molecules shown in the figure (with their anticodons shown in the 3' to 5' direction) are available. Two of them can correctly match the mRNA so that a dipeptide can form. The dipeptide that will form will be

proline-threonine.

Part complete A eukaryotic transcription unit that is 8,000 nucleotides long may use 1,200 nucleotides to make a protein consisting of approximately 400 amino acids. This is best explained by the fact that

many noncoding stretches of nucleotides are present in eukaryotic DNA.

What is the source of the extra chromosome 21 in an individual with Down syndrome?

nondisjunction or translocation in either parent

Cystic fibrosis affects the lungs, the pancreas, the digestive system, and other organs, resulting in symptoms ranging from breathing difficulties to recurrent infections. Which of the following terms best describes this expression of phenotypes?

pleiotropy

Which of the following describes the ability of a single gene to have multiple phenotypic effects?

pleiotropy

Two plants are crossed, resulting in offspring with a 3:1 ratio for a particular trait. What does this suggest?

that the parents were both heterozygous for a single trait

Which of the following characteristics can be determined directly from X-ray diffraction photographs of crystallized DNA?

the diameter of the helix

The leading and the lagging strands of DNA formed during DNA replication 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.

Which of the following is the best description of the addition rule of probability?

the probability that either one of two mutually exclusive events will occur

Part complete There are 61 mRNA codons that specify an amino acid, but only 45 tRNAs. This is best explained by the fact that

the rules for base pairing between the third base of a codon and tRNA are flexible.

DNA template strand 5'___________________________3' DNA complementary strand 3'___________________________5' In the transcription event of the DNA in the figure, where would the promoter be located?

to the right of the template strand

One possible result of chromosomal breakage is for a fragment to join a non-homologous chromosome. What is this alteration called?

translocation

One map unit is equivalent to which of the following values?

1% frequency of recombination between two genes

Part complete Which one of the following is true of tRNAs?

Each tRNA binds a particular amino acid

In DNA from any species, the amount of adenine equals the amount of thymine, and the amount of guanine equals the amount of cytosine. Which of the following investigators was (were) responsible for this discovery?

Erwin Chargaff

Please use the following information to answer the question(s) below. A woman who has blood type A positive has a daughter who is type O positive and a son who is type B negative. Rh positive is a trait that shows simple dominance over Rh negative and is designated by the alleles R and r, respectively. A third gene for the MN blood group has codominant alleles M and N. Which of the following is a possible genotype for the mother?

IAi

Which of the following statements describes the chromosome theory of inheritance as expressed in the early twentieth century?

Mendelian genes are at specific loci on the chromosome and in turn segregate during meiosis.

In his transformation experiments, what did Griffith observe?

Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.

A white-eyed female Drosophila is crossed with a red-eyed male Drosophila. Which statement below correctly describes the results?

None of the females will have white eyes.

Why did the F1 offspring of Mendel's classic pea cross always look like one of the two parental varieties?

One allele was dominant.

A couple has a child with Down syndrome. The mother is 39 years old at the time of delivery. Which of the following is the most probable cause of the child's condition?

One member of the couple underwent nondisjunction in gamete production.

One of two major forms of a human condition called neurofibromatosis (NF 1) is inherited as a dominant allele, although it may range from mildly to very severely expressed. If a young child is the first in her family to be diagnosed, which of the following is the best explanation?

One of the parents has very mild expression of the gene.

Part complete You can use Chargaff's rules to predict the percentage of one or more bases in the DNA of a species if at least one value is known. Data from several papers by Chargaff: for example, E. Chargaff et al., Composition of the desoxypentose nucleic acids of four genera of sea-urchin, Journal of Biological Chemistry 195: 155-160 (1952).

Approximately 28%

Part complete Which of the following events causes recombination between linked genes to occur?

Crossovers between these genes result in chromosomal exchange.

In trying to determine whether DNA or protein is the genetic material, Hershey and Chase made use of which of the following facts?

DNA contains phosphorus, whereas protein does not.

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.

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

DNA polymerase III

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

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

Meselson and Stahl cultured E. coli for several generations in a medium with a heavy isotope of nitrogen, 15N. They transferred the bacteria to a medium with a light isotope of nitrogen, 14 N. After two rounds of DNA replication, half the DNA molecules were light (both strands had 14N) and half were hybrids (15N-14N). What did the researchers conclude from these results?

DNA replication is semiconservative.

The frequency of heterozygosity for the sickle-cell anemia allele is unusually high, presumably because this reduces the frequency of malaria. Such a relationship is related to which of the following concepts?

Darwin's explanation of natural selection

Part complete After mixing a heat-killed, phosphorescent (light-emitting) strain of bacteria with a living, nonphosphorescent strain, you discover that some of the living cells are now phosphorescent. Which observation(s) would provide the best evidence that the ability to phosphoresce is a heritable trait?

Descendants of the living cells are also phosphorescent.

A scientist discovers a DNA-based test for one allele of a particular gene. This and only this allele, if homozygous, produces an effect that results in death at or about the time of birth. Which of the following statements describes the best use of this discovery?

Design a test for identifying heterozygous carriers of the allele.

In E. coli, there is a mutation in a gene called dnaB that alters the helicase that normally acts at the origin. Which of the following would you expect as a result of this mutation?

The DNA strands at the origin of replication will separate, but replication will not progress

The tRNA shown in the figure has its 3' end projecting beyond its 5' end. What will occur at this 3' end?

The amino acid will bind covalently.

Which of the following statements describes one difference between the law of independent assortment and the law of segregation?

The law of independent assortment explains the segregation of two or more genes relative to one another.

What is the reason that closely linked genes are typically inherited together?

The likelihood of a crossover event between these two genes is low.

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.

Part complete Individuals with the disorder xeroderma pigmentosum are hypersensitive to sunlight. This occurs because their cells are impaired in what way?

They cannot repair thymine dimers.

Use the figure and the following description to answer the questions below. In a particular plant, leaf color is controlled by gene locus D. Plants with at least one allele D have dark green leaves, and plants with the homozygous recessive dd genotype have light green leaves. A true-breeding dark-leaved plant is crossed with a light-leaved one, and the F1 offspring is allowed to self-pollinate. The predicted outcome of the F2 is diagrammed in the Punnett square shown in the figure, where 1, 2, 3, and 4 represent the genotypes corresponding to each box within the square. D d D 1 2 d 3 4 Which of the boxes marked 1-4 correspond(s) to plants with dark leaves?

1, 2, and 3

Black fur in mice (B) is dominant to brown fur (b). Short tails (T) are dominant to long tails (t). What fraction of the progeny of crosses BbTt × BBtt will be expected to have black fur and long tails?

1/2

Use the following information to answer the questions below. Skin color in a certain species of fish is inherited via a single gene with four different alleles. One fish of this type has alleles 1 and 3 (S1S3) and its mate has alleles 2 and 4 (S2S4). If each allele confers a unit of color darkness such that S1 has one unit, S2 has two units, and so on, then what proportion of their offspring would be expected to have five units of color?

1/2

What is the probability that they will have a color-blind daughter? Express your answer as a fraction using the slash symbol and no spaces (for example, 1/24)

1/4 for each daughter (1/2 that the child will be female × 1/2 chance of homozygous recessive genotype)

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

100%

A particular triplet of bases in the template strand of DNA is 5' AGT 3'. The corresponding codon for the mRNA transcribed is

3' UCA 5'.

The nitrogenous base adenine is found in all members of which of the following groups of molecules?

ATP, RNA, and DNA

Part complete Two genes of a flower, one controlling blue (B) versus white (b) petals and the other controlling round (R) versus oval (r) stamens, are linked and are 10 map units apart. You cross a homozygous blue-oval plant with a homozygous white-round plant. The resulting F1 progeny are crossed with homozygous white-oval plants, and 1,000 F2 progeny are obtained. How many F2 plants of each of the four phenotypes do you expect? _____ blue-oval : _____ white-round : _____ blue-round : _____ white-oval Express your answer as four whole numbers separated by colons (for example, 400:300:200:100).

450: 450: 50: 50 450 of each blue-oval and white-round (parentals) and 50 each of blue-round and white-oval (recombinants).

Part complete An Okazaki fragment has which of the following arrangements?

5' RNA nucleotides, DNA nucleotides 3'

Part complete Please use the following information to answer the question(s) below. The figure shows a pedigree chart for a family, some of whose members exhibit the dominant trait, W. Affected individuals are indicated by a dark square or circle. What is the likelihood that the offspring of IV-3 and IV-4 will have the trait?

50%

When crossing an organism that is homozygous recessive for a single trait with a heterozygote, what is the chance of producing an offspring with the homozygous recessive phenotype?

50%

the figure shows a map of four genes on a chromosome. The figure shows a map of four genes on a chromosome: A, W, E, and G from left to right. The distance between A and W is 5, between W and E is 3, and between E and G is 12. Between which two genes would you expect the highest frequency of recombination?

A and G

What do we mean when we use the term dihybrid cross?

A dihybrid cross involves organisms that are heterozygous for two characters.

What is the probability that their first son will be color-blind? Express your answer as a fraction using the slash symbol and no spaces (for example, 1/24).

A first son has a 1/2 chance of inheriting the recessive genotype.

The genetic code is essentially the same for all organisms. Based on this information, one can logically assume which of the following statements to be correct?

A gene from an organism can theoretically be expressed by any other organism.

What do we mean when we use the term monohybrid cross?

A monohybrid cross involves organisms that are heterozygous for one character

Which of the following does not occur in prokaryotic gene expression, but does occur in eukaryotic gene expression?

A poly-A tail is added to the 3' end of an mRNA and a cap is added to the 5' end.

Use the following information to answer the questions below. A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows: A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type): The greatest distance among the three genes is between a and c. What does this mean?

Genes are in the order: abc

Part complete Which of the following statements correctly describes one characteristic of histones?

Histone H1 is not present in the nucleosome bead; instead, it draws the nucleosomes together.

Why do histones bind tightly to DNA?

Histones are positively charged, and DNA is negatively charged.

Which of the following statements provides an example of epistasis?

In rabbits and many other mammals, one genotype (ee) prevents any fur color from developing.

Which of the following statements correctly describes alternative RNA splicing?

It can allow the production of proteins of different sizes and functions from a single mRNA.

Which of the following is true of DNA during interphase?

It exists as chromatin and is less condensed than mitotic chromosomes.

Which of the following statements accurately describes why Taq polymerase is used in PCR?

It is heat stable and can withstand the heating step of PCR.

Which of the following is true about a plant with the genotype AABbcc?

It is homozygous at two loci. -An organism having a pair of identical alleles at a given locus is said to be homozygous for that locus. Here, the plant is homozygous at loci A and C.

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

It joins Okazaki fragments together.

What is the function of RNA polymerase?

It unwinds the double helix and adds nucleotides to a growing strand of RNA.

A phenotypically normal prospective couple seeks genetic counseling because the man knows that he has a translocation of a portion of his chromosome 4 that has been exchanged with a portion of his chromosome 12. Although he is normal because his translocation is balanced, he and his wife want to know the probability that his sperm will be abnormal. What is your prognosis regarding his sperm?

One-fourth will be normal, 1/4 will have the translocation, and 1/2 will have duplications and deletions

Part complete Use the following information to answer the questions below. A plantlike organism on the planet Pandora can have three recessive genetic traits: bluish leaves, due to an allele (a) of gene A; a feathered stem, due to an allele (b) of gene B; and hollow roots due to an allele (c) of gene C. The three genes are linked and recombine as follows: A geneticist did a testcross with an organism that had been found to be heterozygous for the three recessive traits and she was able to identify progeny of the following phenotypic distribution (+ = wild type): What is the greatest benefit of having used a testcross for this experiment?

Progeny can be scored by their phenotypes alone.

A mutant bacterial cell has a defective aminoacyl-tRNA synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. What would be a potential consequence for a cell in which this happens? Remember that phenylalanine may be encoded by multiple codons.

Proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.

If Chargaff's equivalence rule is valid, then hypothetically we could extrapolate this to the combined genomes of all species on Earth (as if there were one huge Earth genome). In other words, the total amount of A in every genome on Earth should equal the total amount of T in every genome on Earth. Likewise, the total amount of G in every genome on Earth should equal the total amount of C in every genome on Earth.

Yes, the average for A approximately equals the average for T, and the average for G approximately equals the average for C.

In certain plants, the tall trait is dominant to the short trait. If a heterozygous plant is crossed with a homozygous tall plant, what is the probability that the offspring will be short?

Zero

In order for a eukaryotic gene to be engineered into a bacterial colony to be expressed, what must be included in addition to the coding exons of the gene?

a bacterial promoter sequence

Which of the following types of mutation, resulting in an error in the mRNA just after the 3 AUG start codon, is likely to have the most serious effect on the polypeptide product?

a deletion of two nucleotides

Which of the following is known as a Philadelphia chromosome?

a human chromosome 22 that has had a specific translocation

Chapter 12: Normally, only female cats have the tortoiseshell phenotype because

a male inherits only one allele of the X-linked gene controlling hair color.

Part complete Which of the following mutations is most likely to cause a phenotypic change?

a single nucleotide deletion in an exon coding for an active site of a protein

Which of the following descriptions of nucleotide triplets best represents a codon?

a triplet in the same reading frame as an upstream AUG

What event causes all female mammals to have one active X chromosome per cell instead of two?

activation of the XIST gene on the X chromosome that will become the Barr body

Mendel's second law of independent assortment has its basis in which of the following events of meiosis I?

alignment of synapsed pairs of homologous chromosomes on the metaphase plate

The figure shows the simple metabolic pathway. Enzyme 1 catalyzes the transformation of A into B and enzyme 2 catalyzes the transformation of B into C. Examine the simple metabolic pathway in the figure. A mutation results in a defective enzyme 1. Which of the following results would be a consequence of that mutation?

an accumulation of A and no production of B and C

What is an allele?

an alternative version of a gene - A diploid organism carries two alleles for each autosomal gene. The two alleles are found at comparable locations (loci) on homologous chromosomes. The alleles may be identical or slightly different, but they affect the same genetic character.

Part complete When the ribosome reaches a stop codon on the mRNA, no corresponding tRNA enters the A site. If the translation reaction were to be experimentally stopped at this point, which of the following sets of structures would you be able to isolate from the cell?

an assembled ribosome with a polypeptide attached to the tRNA in the P site

Mendel's observation of the segregation of alleles in gamete formation has its basis in which of the following phases of cell division?

anaphase I of meiosis

Use the following pedigree (the figure) for a family in which dark-shaded symbols represent individuals with one of the two major types of colon cancer. Numbers under the symbols are the individual's age at the time of diagnosis. A slash through the symbol indicates that the individual is deceased. From this pedigree, how does this trait seem to be inherited?

as a dominant trait

How does a bacterial cell protect its own DNA from restriction enzymes?

by adding methyl groups to adenines and cytosines

Use the following information to answer the next few questions. A eukaryotic gene has "sticky ends" produced by the restriction endonuclease EcoRI. The gene is added to a mixture containing EcoRI and a bacterial plasmid that carries two genes conferring resistance to ampicillin and tetracycline. The plasmid has one recognition site for EcoRI located in the tetracycline resistance gene. This mixture is incubated for several hours, exposed to DNA ligase, and then added to bacteria growing in nutrient broth. The bacteria are allowed to grow overnight and are streaked on a plate using a technique that produces isolated colonies that are clones of the original. Samples of these colonies are then grown in four different media: nutrient broth plus ampicillin, nutrient broth plus tetracycline, nutrient broth plus ampicillin and tetracycline, and nutrient broth without antibiotics. Bacteria that contain the plasmid, but not the eukaryotic gene, would grow

in all four types of broth.

After an RNA molecule is transcribed from a eukaryotic gene, what is removed and what is spliced together to produce an mRNA molecule with a continuous coding sequence?

introns ... exons

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

males are hemizygous for the X chromosome.