MB Tutorial DNA & Genetics

Glucose-6-phosphate dehydrogenase deficiency (G6PD) is inherited as a recessive allele of an X-linked gene in humans. A woman whose father suffered from G6PD marries a normal man.(a) What proportion of their sons is expected to be G6PD?(b) If the husband was not normal but was G6PD deficient, would you change your answer in part (a)?

(a) 1/2; (b) no

In a Drosophila experiment, a cross was made between homozygous wild-type females and yellow-bodied males. All of the resulting F1s were phenotypically wild type. However, adult flies of the F2 generation (resulting from matings of the F1s) had the characteristics shown in the figure above. Consider the following question:(a) Is the mutant allele for yellow body recessive or dominant?(b) Is the yellow locus autosomal (not X-linked) or X-linked?

(a) recessive; (b) X-linked

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. Which of the boxes marked 1-4 correspond to plants that will be true-breeding?

1 and 4 only

Which of the progeny phenotypes will require recombination between genes A and B?

1, 2, 5, and 6

A recessive allele on the X chromosome is responsible for red-green color blindness in humans. A woman with normal vision whose father is color blind marries a color-blind male. What is the probability that this couple's first son will be color blind?

1/2

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

The pattern of inheritance (monohybrid, dihybrid, sex-linked, and genes linked on the same chromosomes) can be predicted from data if one is given the parent or offspring genotypes or phenotypes. Two organisms, with genotypes BbDD and BBDd, are mated. Assuming independent assortment of the B/b and D/d genes, determine the genotypic ratios in offspring that would occur.

1/4 BBDD 1/4 BbDD 1/4 BBDd 1/4 BbDd

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%

A homozygous tomato plant with red fruit and yellow flowers was crossed with a homozygous tomato plant with golden fruit and white flowers. The F1 all had red fruit and yellow flowers. The F1 were testcrossed by crossing them to homozygous recessive individuals and the following offspring were obtained: Red fruit and yellow flowers-41 Red fruit and white flowers-7 Golden fruit and yellow flowers-8 Golden fruit and white flowers-44 How many map units separate these genes?

15

In rabbits, the homozygous CC is normal, Cc results in deformed legs, and cc results in very short legs. The genotype BB produces black fur, Bb brown fur, and bb white fur. If a cross is made between brown rabbits with deformed legs and white rabbits with deformed legs, what percentage of the offspring would be expected to have deformed legs and white fur?

25%

In birds, sex is determined by a ZW chromosome scheme. Males are ZZ and females are ZW. A recessive lethal allele that causes death of the embryo is sometimes present on the Z chromosome in pigeons. What would be the sex ratio in the offspring of a cross between a male that is heterozygous for the lethal allele and a normal female?

2:1 male to female

If recombination frequency is equal to distance in map units, what is the approximate distance between genes A and B?

3 map units

Hershey and Chase used _____ to radioactively label the T2 phage's proteins.

35S Hershey and Chase used radioactive sulfur to label the phage's proteins.

Which of the following are the phenotypes of the parents in this cross?

4 and 8

Nucleic acids are assembled in the _____ direction.

5' to 3'

How many unique gametes could be produced through independent assortment by an individual with the genotype AaBbCCDdEE?

8

Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cactuses have dull spines. At the same time, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. If doubly heterozygous SsNn cactuses were allowed to self-pollinate, the F2 would segregate in which of the following ratios?

9 sharp-spined:3 dull-spined:4 spineless

In humans, ABO blood types refer to glycoproteins in the membranes of red blood cells. There are three alleles for this autosomal gene: IA, IB, and i. The IA allele codes for the A glycoprotein, The IB allele codes for the B glycoprotein, and the i allele doesn't code for any membrane glycoprotein. IA and IB are codominant, and i is recessive to both IA and IB. People with type A blood have the genotypes IAIA or IAi, people with type B blood are IBIB or IBi, people with type AB blood are IAIB, and people with type O blood are ii. If a woman with type AB blood marries a man with type O blood, which of the following blood types could their children possibly have?

A and B

The following is a map of four genes on a chromosome Between which two genes would you expect the highest frequency of recombination?

A and G

Which of the following is true regarding this new fetal DNA test?

A decreased number of false positive tests for both Down syndrome and Trisomy 18.

If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred

A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell.

If a diploid cell undergoes meiosis and produces two gametes with n + 1 chromosomes and two gametes with n− 1 chromosomes, what type of error occurred

A nondisjunction error occurred in meiosis I, in which both members of a homologous pair migrated to the same pole of the cell. When this type of error occurs, half of the gametes receive one too many chromosomes, and the other half receive one too few. When all of the gametes are affected, the error probably occurred in meiosis I.

If a diploid cell undergoes meiosis and produces two gametes that are normal, and one with n − 1 chromosomes, and one with n + 1 chromosomes, what type of error occurred?

A nondisjunction error occurred in meiosis II, in which both sister chromatids of a chromosome migrated to the same pole of the cell.

What kind of cell results when a diploid and a haploid gamete fuse during fertilization?

A triploid cell A triploid cell has three sets of chromosomes: the two from the diploid gamete and the one from the haploid gamete.

Refer to the figure above. What bases will be added to the primer as DNA synthesis proceeds? The bases should appear in the new strand in the order that they will be added starting at the 3' end of the primer. (Note that the primer shown is composed of DNA, not RNA, nucleotides which is often the case in test-tube DNA synthesis such as PCR.)

A, G, A, C, G, A, C

What is a nondisjunction?

An error in cell division that causes homologous chromosomes or sister chromatids to move to the same side of the dividing cell Nondisjunction refers to the failure of pairs of chromosomes or sister chromatids to separate during meiosis or mitosis.

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. Which of the following is a possible phenotype for the father?

B positive

Recombination between linked genes comes about for what reason?

Crossovers between these genes result in chromosomal exchange.

The radioactive isotope 32P labels the T2 phage's _____.

DNA The T2 phage consists of a protein coat and DNA. It is the DNA that contains P.

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 of these is a difference between a DNA and an RNA molecule?

DNA is usually double-stranded, whereas RNA is usually single-stranded.

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

DNA contains the template needed to copy itself, but it has no catalytic activity in cells. What catalyzes the formation of phosphodiester bonds between adjacent nucleotides in the DNA polymer being formed?

DNA polymerase

What catalyzes DNA synthesis?

DNA polymerase This enzyme catalyzes DNA synthesis.

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

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

Why is the new DNA strand complementary to the 3' to 5' strands assembled in short segments?

DNA polymerase can assemble DNA only in the 5' to 3' direction Since DNA polymerase can assemble DNA only in the 5' to 3' direction, the new strand complementary to the 3' to 5' strand must be assembled either in short 5' to 3' segments, which are later joined together by ligase, or be assembled continuously.

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.

Drag the labels to their appropriate locations in the diagram to describe the name or function of each structure. Use pink labels for the pink targets and blue labels for the blue targets.

During replication, DNA synthesis occurs in the 5′ to 3′ direction along both template strands. On one template strand, synthesis proceeds continuously toward the replication fork, generating the leading strand. On the other template strand, DNA is synthesized away from the replication fork in segments called Okazaki fragments, generating the lagging strand. Several proteins are involved in DNA replication, including the following: Topoisomerase cuts, swivels, and rejoins DNA strands ahead of the replication fork. Helicase breaks the hydrogen bonds between the parental DNA strands and unwinds the double helix. Single-strand binding proteins bind to the single strands of DNA, preventing them from re-forming hydrogen bonds with each other and allowing synthesis to occur on both strands. DNA polymerase III synthesizes the new strands, but it requires an existing 3′ hydroxyl (—OH) group to add nucleotides. Primase creates short RNA primers, initiating DNA synthesis on both template strands. DNA polymerase I removes the RNA primers and replaces them with DNA nucleotides. On the lagging strand, DNA ligase joins Okazaki fragments by forming phosphodiester bonds between them, thus completing DNA replication.

A gene for the MN blood group has codominant alleles M and N. If both children are of blood type M, which of the following is possible?

Each parent is either M or MN.

Imagine a human disorder that is inherited as a dominant, X-linked trait. How would the frequency of this disorder vary between males and females?

Females would display this disorder with greater frequency than males. Men have only one X chromosome, whereas women have two. Thus, women have twice the chance of inheriting the dominant allele that causes this disorder. Remember that the disorder is caused by a dominant allele, so an individual who inherits a single dominant allele will display the disorder. Read about the inheritance of X-linked genes.

The greatest distance among the three genes is between a and c. What does this mean?

Genes are in the order: abc.

A sexually reproducing animal has two unlinked genes, one for head shape (H) and one for tail length (T). Its genotype is HhTt. Which of the following genotypes is possible in a gamete from this organism?

HT

Who demonstrated that DNA is the genetic material of the T2 phage?

Hershey and Chase

Select the correct explanation for the fact that a carrier of a recessive genetic disorder does not have the disorder.

In a recessive disorder, only a single functioning allele is necessary to determine a normal phenotype.

The male gamete determines sex because each male gamete can contribute either an X or a Y chromosome.

In humans, the male produces both X- and Y-bearing sperm, whereas females only produce X-bearing eggs.

When can nondisjunction occur? Choose the best answer.

In meiosis, when sister chromatids fail to separate In meiosis, when homologous chromosomes fail to separate In mitosis, when sister chromatids fail to separateAll three answers are correct Nondisjunction errors can occur in meiosis I, when homologous chromosomes fail to separate, or in either mitosis or meiosis II, when sister chromatids fail to separate.

How is the fetal DNA used in this new screening tool unique?

It is not from a cell, but is floating freely in the mother's blood.

Marfan syndrome in humans is caused by an abnormality of the connective tissue protein fibrillin. Patients are usually very tall and thin, with long spindly fingers, curvature of the spine, sometimes weakened arterial walls, and sometimes ocular problems, such as lens dislocation. Which of the following would you conclude about Marfan syndrome from this information?

It is pleiotropic.

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

It joins Okazaki fragments together.

Which of the following best summarizes current research on this new fetal DNA test?

It works well for finding errors in chromosome number.

Who performed classic experiments that supported the semiconservative model of DNA replication?

Meselson and Stahl

Genomic imprinting is generally due to the addition of methyl (CH3) groups to C nucleotides and chemical histone changes to silence a given gene. If this depends on the sex of the parent who transmits the gene, which of the following must be true?

Methylation must be reversible in ovarian and testicular cells.

Which of the following statements is a correct explanation for the observation that all offspring exhibit a phenotype for a particular trait that appears to be a blend of the two parental varieties?

Neither of the parental genes is dominate over the other.

What is an adaptive advantage of recombination between linked genes?

New allele combinations are acted upon by natural selection.

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?

No replication fork will be formed.

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 twenties. How likely is it for a woman to have this condition?

One-half of the daughters of an affected father and a carrier mother could have this condition.

Which part of a deoxynucleoside triphosphate (dNTP) molecule provides the energy for DNA synthesis?

Phosphate groups

Which of the following enzymes creates a primer for DNA polymerase?

Primase

Which of the following statements about DNA synthesis is true?

Primers are short sequences that allow the initiation of DNA synthesis. When a primer is added to a single strand of DNA, DNA polymerase can start adding nucleotides to synthesize a complementary strand.

Quantitative characters vary in a population along a continuum. How do such characters differ from the characters investigated by Mendel in his experiments on peas?

Quantitative characters are due to polygenic inheritance, the additive effects of two or more genes on a single phenotypic character. A single gene affected all but one of the pea characters studied by Mendel.

The synthesis of a new strand begins with the synthesis of a(n) _____.

RNA primer complementary to a preexisting DNA strand The synthesis of a DNA strand begins with the formation of an RNA primer.

You cross a true-breeding red-flowered snapdragon with a true-breeding white-flowered one. All of the F1 are pink. What does this say about the parental traits?

Red shows incomplete dominance over white. Red shows incomplete dominance over white, and the F1 is therefore pink.

In E. coli replication the enzyme primase is used to attach a 5 to 10 base ribonucleotide strand complementary to the parental DNA strand. The RNA strand serves as a starting point for the DNApolymerase that replicates the DNA. If a mutation occurred in the primase gene, which of the following would you expect?

Replication would not occur on either the leading or lagging strand.

Telomere shortening puts a limit on the number of times a cell can divide. Research has shown that telomerase can extend the life span of cultured human cells. How might adding telomerase affect cellular aging?

Telomerase eliminates telomere shortening and retards 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.

Gregor Mendel set up a dihybrid cross with one pea plant from the parental generation (P) producing round yellow peas and the other pea plant producing wrinkled green peas. The F2 generation included 315 plants producing round yellow peas, 108 with round green peas, 101 with wrinkled yellow peas, and 32 with wrinkled green peas. How would these results have differed if pea shape and pea color had been linked genes, located close together on the same chromosome?

The F2 generation would have included a higher percentage of pea plants producing round, yellow peas. If pea shape and pea color were determined by closely linked genes, they would not show independent assortment. Chromosomes would carry the combination of alleles seen in the P generation: yellow + round or green + wrinkled. Approximately ¾ or 75% of the F2 generation would inherit at least one chromosome carrying the yellow + round alleles. That is higher than Mendel's observed percentage of 315/556 or 56%. Read how linkage affects inheritance.

Which of the following is true?

The chance of having a child with a chromosomal abnormality increases with the age of the mother.

Look at the Punnett square, which shows the predicted offspring of the F2 generation from a cross between a plant with yellow-round seeds (YYRR) and a plant with green-wrinkled seeds (yyrr). Select the correct statement about wrinkled yellow seeds in the F2 generation.

The chance that an individual taken at random from the F2 generation produces wrinkled seeds is 25% and the chance that the same individual produces yellow seeds is 75%. Read about the Law of Independent Assortment and about how to solve complex genetics problems using the rules of probability.

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.

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.

Which of the following is true of an X-linked gene, but not of a Y-linked gene?

The gene is present in both males and females. All cells have at least one functional X chromosome.

Which of the following statements about independent assortment and segregation is correct?

The law of independent assortment requires describing two or more genes relative to one another. Submit

What is the difference between the leading strand and the lagging strand in DNA replication?

The leading strand is synthesized continuously in the 5' → 3' direction, while the lagging strand is synthesized discontinuously in the 5' → 3' direction.

DNA is a self-replicating molecule. What accounts for this important property of DNA?

The nitrogenous bases of the double helix are paired in specific combinations: A with T and G with C. Because of the specificity of the pairing of the nitrogenous bases, each strand of the double helix specifies the matching sequence of bases on the other strand. During replication, when the strands separate, each strand serves as a template for the replication of other strand. Read about base pairing in DNA. Return to Assignment

Which of these is(are) purines?

The one-carbon nitrogen ring bases (thymine and cytosine) are pyrimidines.

What is the greatest benefit of having used a testcross for this experiment?

The phenotypes of the progeny reveal the allelic content of the gamete from the heterozygous parent.

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.

Which of these is(are) pyrimidines?

The two-carbon nitrogen ring bases (adenine and guanine) are purines

Each chromosome in this homologous pair possesses a different allele for flower color. Which statement about this homologous pair of chromosomes is correct?

These homologous chromosomes represent a maternal and a paternal chromosome.

Which of the following statements about Okazaki fragments in E. coli is true?

They are formed on the lagging strand of DNA.

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

They are located close together on the same chromosome.

When a dominant allele coexists with a recessive allele in a heterozygote individual, how do they interact with each other?

They do not interact at all.

Which of the following enzymes is important for relieving the tension in a helix as it unwinds during DNA synthesis?

Topoisomerase This enzyme untwists the coils that occur in the DNA as it is being unwound into a single-stranded template.

What was the most significant conclusion that Gregor Mendel drew from his experiments with pea plants?

Traits are inherited in discrete units and are not the results of "blending."

Of the following chromosomal abnormalities, which type is most likely to be viable in humans?

Trisomy Some trisomies are viable in humans, but they result in developmental abnormalities, such as Down syndrome (trisomy 21). Only humans with trisomies of the small chromosomes (13, 18, or 21) or the sex chromosomes survive past birth.

True or false? Single-stranded DNA molecules are said to be antiparallel when they are lined up next to each other but oriented in opposite directions.

True When the 3' end of one DNA strand points in the same direction as the 5' end of the other DNA strand, the strands are said to be antiparallel.

Which syndrome is characterized by the XO chromosome abnormality?

Turner syndrome Turner syndrome is characterized by a chromosome pattern of XO, or one X chromosome and no Y chromosome.

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?

XNXn and XNY

What is the definition of one map unit?

a 1% frequency of recombination between two genes

Height in humans generally shows a normal (bell-shaped) distribution. What type of inheritance most likely determines height?

a combination of polygenic inheritance and environmental factors Several genes (polygenic inheritance) control height in humans, giving an overall normal distribution. Environmental factors such as nutrition smooth out the curve.

SRY is best described as _____.

a gene region present on the Y chromosome that triggers male development

Normally, only female cats have the tortoiseshell phenotype because _____.

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

In humans, clear gender differentiation occurs, not at fertilization, but after the second month of gestation. What is the first event of this differentiation?

activation of SRY in male embryos and masculinization of the gonads

All female mammals have one active X chromosome per cell instead of two. What causes this?

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

A man who carries an allele of an X-linked gene will pass it on to _____.

all of his daughters

Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cactuses have dull spines. At the same time, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. A cross between a true-breeding sharp-spined cactus and a spineless cactus would produce_____.

all sharp-spined progeny

An obstetrician knows that one of her patients is a pregnant woman whose fetus is at risk for a serious disorder that is detectable biochemically in fetal cells. The obstetrician would most reasonably offer which of the following procedures to her patient?

amniocentesis or CVS

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.

What results if a fragment of a chromosome breaks off and then reattaches to the original chromosome at the same place but in the reverse direction?

an inversion

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

b-rb-cn-vg

Your 28 year old friend is pregnant. Which of the following screenings is she most likely to initially have to test for Down syndrome?

blood test

Feather color in budgies is determined by two different genes, Y and B, one for pigment on the outside and one for the inside of the feather. YYBB, YyBB, YYBb or YyBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white. A blue budgie is crossed with a white budgie. Which of the following results is possible?

blue and white offspring

Correns found that the inheritance of variegated color on the leaves of certain plants was determined only by the maternal parent. What phenomenon explains this pattern?

chloroplast inheritance

After DNA replication is completed, _____.

each new DNA double helix consists of one old DNA strand and one new DNA strand

Hydrangea plants of the same genotype are planted in a large flower garden. Some of the plants produce blue flowers and others pink flowers. This can be best explained by which of the following?

environmental factors such as soil pH

Gene S controls the sharpness of spines in a type of cactus. Cactuses with the dominant allele, S, have sharp spines, whereas homozygous recessive ss cactuses have dull spines. At the same time, a second gene, N, determines whether or not cactuses have spines. Homozygous recessive nn cactuses have no spines at all. The relationship between genes S and N is an example of _____.

epistasis

How are human mitochondria inherited?

from the mother only An individual's mitochondria are all derived from those found in the ovum.

The law of independent assortment states that each pair of alleles segregates independently of all other pairs of alleles during _________ formation

gamete

In Drosophila melanogaster, vestigial wings are caused by a recessive allele of a gene that is linked to a gene with a recessive allele that causes black body color. Morgan crossed black-bodied, normal-winged females and gray-bodied, vestigial-winged males. The F1 were all gray bodied, normal winged. The F1 females were crossed to homozygous recessive males to produce testcross progeny. Morgan calculated the map distance to be 17 map units. Which of the following is correct about the testcross progeny?

gray-bodied, normal-winged flies PLUS black-bodied, vestigial-winged flies = 17% of the total

A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was six 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

The first step in the replication of DNA is catalyzed by _____.

helicase The first step of DNA replication is unwinding the DNA double helix.

In a nucleosome, the DNA is wrapped around

histones

What can we observe in order to visualize Mendel's Law of Segregation?

homologous chromosomes separating during meiosis I Homologous chromosomes each carry an allele for every gene. Those alleles may be the same or different, but they are segregated during meiosis I and distributed to each gamete.

In general, the frequency with which crossing over occurs between two linked genes depends on what?

how far apart they are on the chromosome The farther apart two genes are, the greater the probability that a crossover will occur between them, and therefore the greater the recombination frequency.

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The flower color trait in radishes is an example of which of the following?

incomplete dominance

After allowing phages grown with bacteria in a medium that contained 32P and 35S, Hershey and Chase used a centrifuge to separate the phage ghosts from the infected cell. They then examined the infected cells and found that they contained _____, which demonstrated that _____ is the phage's genetic material.

labeled DNA ... DNA

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

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

males are hemizygous for the X chromosome

A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was six 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. How many of their daughters might be expected to be color-blind dwarfs?

none

In E. coli, to repair a thymine dimer by nucleotide excision repair, in which order do the necessary enzymes act?

nuclease, DNA polymerase I, DNA ligase

The spontaneous loss of amino groups from adenine in DNA results in hypoxanthine, an uncommon base, opposite thymine. What combination of proteins could repair such damage?

nuclease, DNA polymerase, DNA ligase

E. coli cells grown on 15N15N medium are transferred to 14N14N medium and allowed to grow for two more generations (two rounds of DNA replication). DNA extracted from these cells is centrifuged. What density distribution of DNA would you expect in this experiment?

one low-density and one intermediate-density band

This is an image of a _____.

phage

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

pleiotropy

Radish flowers may be red, purple, or white. A cross between a red-flowered plant and a white-flowered plant yields all-purple offspring. The part of the radish we eat may be oval or long, with long being the dominant trait. If true-breeding red long radishes are crossed with true-breeding white oval radishes, the F1 will be expected to be which of the following?

purple and long

Pseudohypertrophic muscular dystrophy is a human disorder that causes gradual deterioration of the muscles. Only boys are affected, and they are always born to phenotypically normal parents. Due to the severity of the disease, the boys die in their teens. Is this disorder likely to be caused by a dominant or recessive allele? Is its inheritance sex-linked or autosomal?

recessive, sex-linked

What is the function of topoisomerase?

relieving strain in the DNA ahead of the replication fork

The action of helicase creates _____.

replication forks and replication bubbles A replication fork is the transition region between paired and unpaired DNA strands.

In cattle, roan coat color (mixed red and white hairs) occurs in the heterozygous (Rr) offspring of red (RR) and white (rr) homozygotes. Which of the following crosses would produce offspring in the ratio of 1 red:2 roan:1 white?

roan × roan

Which of the following is an example of polygenic inheritance?

skin pigmentation in humans

You can tell that this is an image of a DNA nucleotide and not an RNA nucleotide because you see a _____.

sugar with two, and not three, oxygen atoms

An old DNA strand is used as a _____ for the assembly of a new DNA strand.

template An old DNA strand is used as a template for the synthesis of a complementary new strand.

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

Which of these nitrogenous bases is found in DNA but not in RNA?

thymine

In a DNA double helix an adenine of one strand always pairs with a(n) _____ of the complementary strand, and a guanine of one strand always pairs with a(n) _____ of the complementary strand.

thymine ... cytosine apple tree go cart

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

Sex determination in mammals is due to the SRY gene. Which of the following could allow a person with an XX karyotype to develop a male phenotype?

translocation of SRY to a X chromosome

Feather color in budgies is determined by two different genes, Y and B, one for pigment on the outside and one for the inside of the feather. YYBB, YyBB, or YYBb is green; yyBB or yyBb is blue; YYbb or Yybb is yellow; and yybb is white. Two blue budgies were crossed. Over the years, they produced twenty-two offspring, five of which were white. What are the most likely genotypes for the two blue budgies?

yyBb and yyBb