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Questions and Answers of Biology

Suppose that a gene affects the anterior morphology in house flies and is inherited as a maternal effect gene. The gene exists in a normal allele, H, and a recessive allele, h, which causes a small
Explain why maternal effect genes exert their effects during the early stages of development.
As described in Chapter 21, researchers have been able to clone mammals by fusing a cell having a diploid nucleus (i.e., a somatic cell) with an egg that has had its nucleus removed. A. With regard
Figure 5.1 describes an example of a maternal effect gene. Explain how Sturtevant deduced a maternal effect gene based on the F2 and F3 generations.
Chapter 20 describes a blotting method known as Northern blotting that is used to determine the amount of mRNA produced by a particular gene. In this method, the amount of a specific mRNA produced by
A variegated trait in plants is analyzed using reciprocal crosses. The following results are obtained: Variegated female × Normal male Normal female × Variegated male ↓ ↓ 1024 variegated +
Discuss the types of experimental observations that Mary Lyon brought together in proposing her hypothesis concerning X-chromosome inactivation. In your own words, explain how these observations were
Chapter 20 describes three blotting methods (i.e., Southern blotting, Northern blotting, and Western blotting) used to detect specific genes and gene products. Southern blotting detects DNA, Northern
As a hypothetical example, a trait in mice results in mice with long tails. You initially have a true-breeding strain with normal tails and a true-breeding strain with long tails. You then make the
You have a female snail that coils to the right, but you do not know its genotype. You may assume that right coiling (D) is dominant to left coiling (d). You also have male snails of known genotype.
On a camping trip, you find one male snail on a deserted island that coils to the right. However, in this same area, you find several shells (not containing living snails) that coil to the left.
Figure 5.6 describes the results of X-chromosome inactivation in mammals. If fast and slow alleles of glucose-6-phosphate dehydrogenase (G-6-PD) exist in other species, what would be the expected
Two male mice, which we will call male A and male B, are both phenotypically normal. Male A was from a litter that contained half phenotypically normal mice and half dwarf mice. The mother of male A
In the experiment of Figure 5.6, why does a clone of cells produce only one type of G-6-PD enzyme? What would you expect to happen if a clone was derived from an early embryonic cell? Why does the
Recessive maternal effect genes are identified in flies (for example) when a phenotypically normal mother cannot produce any normal offspring. Because all of the offspring are dead, this female fly
According to the endosymbiosis theory, mitochondria and chloroplasts are derived from bacteria that took up residence within eukaryotic cells. At one time, prior to being taken up by eukaryotic
What is the difference in meaning between the terms genetic recombination and crossing over?
In humans, a rare dominant disorder known as nail-patella syndrome causes abnormalities in the fingernails, toenails, and kneecaps. Researchers have examined family pedigrees with regard to this
When true-breeding mice with brown fur and short tails (BBtt) were crossed to true-breeding mice with white fur and long tails (bbTT), all F1 offspring had brown fur and long tails. The F1 offspring
If the likelihood of a single crossover in a particular chromosomal region is 10%, what is the theoretical likelihood of a double or triple crossover in that same region? How would positive
In most two-factor crosses involving linked genes, we cannot tell if a double crossover between the two genes has occurred because the offspring will inherit the nonrecombinant pattern of alleles.
Researchers have discovered that some regions of chromosomes are much more likely than others to cross over. We might call such a region a "hot spot" for crossing over. Lets suppose that two genes,
Describe the unique features of ascomycetes that lend themselves to genetic analysis.
In fungi, what is the difference between a tetrad and an octad? What cellular process occurs in an octad that does not occur in a tetrad?
Explain the difference between an unordered versus an ordered octad.
When applying a chi square approach in a linkage problem, explain why an independent assortment hypothesis is used.
What is mitotic recombination? A heterozygous individual (Bb) with brown eyes has one eye with a small patch of blue. Provide two or more explanations for how the blue patch may have occurred.
Mitotic recombination can occasionally produce a twin spot. Let's suppose an animal species is heterozygous for two genes that govern fur color and length: One gene affects pigmentation, with dark
A crossover has occurred in the bivalent shown here. two chromatids it would involve and where it would occur (i.e., between which two genes) to produce the types of chromosomes shown here:What is
If you try to throw a basketball into a basket, the likelihood of succeeding depends on the size of the basket. It is more likely that you will get the ball into the basket if the basket is bigger.
By conducting testcrosses, researchers have found that the sweet pea has seven linkage groups. How many chromosomes would you expect to find in leaf cells?
Figure 6.1 shows the First experimental results that indicated linkage between two different genes. Conduct a chi square analysis to confirm that the genes are really linked and the data could not be
Two genes are located on the same chromosome and are known to be 12 mu apart. An AABB individual was crossed to an aabb individual to produce AaBb offspring. The AaBb offspring were then crossed to
Two genes, designated A and B, are located 10 mu from each other. A third gene, designated C, is located 15 mu from B and 5 mu from A. The parental generation consisting of AA bb CC and aa BB cc
Two genes in tomatoes are 61 mu apart; normal fruit (F) is dominant to fasciated (flattened) fruit (f), and normal numbers of leaves (Lf) is dominant to leafy (lf). A true-breeding plant with normal
In the tomato, three genes are linked on the same chromosome. Tall is dominant to dwarf, skin that is smooth is dominant to skin that is peachy, and fruit with a normal rounded tomato shape is
A trait in garden peas involves the curling of leaves. A two-factor cross was made by crossing a plant with yellow pods and curling leaves to a wild-type plant with green pods and normal leaves. All
In mice, the gene that encodes the enzyme inosine triphosphatase is 12 mu from the gene that encodes the enzyme ornithine decarboxylase. Suppose you have identified a strain of mice homozygous for a
In the garden pea, several different genes affect pod characteristics. A gene affecting pod color (green is dominant to yellow) is approximately 7 mu away from a gene affecting pod width (wide is
A sex-influenced trait is dominant in males and causes bushy tails. The same trait is recessive in females. Fur color is not sex influenced. Yellow fur is dominant to white fur. A true-breeding
Three recessive traits in garden pea plants are as follows: yellow pods are recessive to green pods, bluish green seedlings are recessive to green seedlings, creeper (a plant that cannot stand up) is
In mice, a trait called snubnose is recessive to a wild-type nose, a trait called pintail is dominant to a normal tail, and a trait called jerker (a defect in motor skills) is recessive to a normal
In Drosophila, an allele causing vestigial wings is 12.5 mu away from another allele that causes purple eyes. A third gene that affects body color has an allele that causes black body color. This
Three autosomal genes are linked along the same chromosome. The distance between gene A and B is 7 mu, the distance between B and C is 11 mu, and the distance between A and C is 4 mu. An individual
Lets suppose that two different X-linked genes exist in mice, designated with the letters N and L. Gene N exists in a dominant, normal allele and in a recessive allele, n, that is lethal. Similarly,
The alleles his-5 and lys-l, found in bakers yeast, result in cells that require histidine and lysine for growth, respectively. A cross was made between two haploid yeast strains that are his-5 lys-l
The experiment of Figure 6.7 is not like a standard testcross, because neither parent is homozygous recessive for both genes. If you were going to carry out this same kind of experiment to verify
How would you determine that genes in mammals are located on the Y chromosome linkage group? Is it possible to conduct crosses (let's say in mice) to map the distances between genes along the Y
Explain the rationale behind a testcross. Is it necessary for one of the parents to be homozygous recessive for the genes of interest? In the heterozygous parent of a testcross, must all of the
In your own words, explain why a testcross cannot produce more than 50% recombinant offspring. When a testcross does produce 50% recombinant offspring, what do these results mean?
Explain why the percentage of recombinant offspring in a testcross is a more accurate measure of map distance when two genes are close together. When two genes are far apart, is the percentage of
If two genes are more than 50 mu apart, how would you ever be able to show experimentally that they are located on the same chromosome?
In Morgan's three-factor testcross of Figure 6.3, he realized that crossing over was more frequent between the eye color and wing length genes than between the body color and eye color genes. Explain
In mice, a dominant allele that causes a short tail is located on chromosome 2. On chromosome 3, a recessive allele causing droopy ears is 6 mu away from another recessive allele that causes a flaky
The terms conjugation, transduction, and transformation are used to describe three different natural forms of genetic transfer between bacterial cells. Briefly discuss the similarities and
What is cotransduction? What determines the likelihood that two genes will be cotransduced?
As described in Figure 7.10, host DNA is hydrolyzed into small pieces, which are occasionally assembled with phage proteins, creating a phage with bacterial chromosomal DNA. If the breakage of the
Describe the steps that occur during bacterial transformation. What is a competent cell? What factors may determine whether a cell will be competent?
Researchers who study the molecular mechanism of transformation have identified many proteins in bacteria that function in the uptake of DNA from the environment and its recombination into the host
Antibiotics such as tetracycline, streptomycin, and bacitracin are small organic molecules that are synthesized by particular species of bacteria. Microbiologists have hypothesized that the reason
What does the term complementation mean? If two different mutations that produce the same phenotype can complement each other, what can you conclude about the locations of each mutation?
Intragenic mapping is sometimes called interallelic mapping. Explain why the two terms mean the same thing. In your own words, explain what an intragenic map is.
As discussed in Chapter 12, genes are composed of a sequence of nucleotides. A typical gene in a bacteriophage is a few hundred or a few thousand nucleotides in length. If two different strains of
Conjugation is sometimes called "bacterial mating." Is it a form of sexual reproduction? Explain.
If you mix together an equal number of F' and F cells, how would you expect the proportions to change over time? In other words, do you expect an increase in the relative proportions of F+ or of F-
What is the difference between an F+ and an Hfr strain? Which type of strain do you expect to transfer many bacterial genes to recipient cells?
What is the role of the origin of transfer during F+ - and Hfr- mediated conjugation? What is the significance of the direction of transfer in Hfr-mediated conjugation?
Each species of bacteria has its own distinctive cell surface. The characteristics of the cell surface play an important role in processes such as conjugation and transduction. For example, certain
Briefly describe the lytic and lysogenic cycles of bacteriophages. In your answer, explain what a prophage is.
In a PI transduction experiment, the PI lysate contains phages that carry pieces of the host chromosomal DNA, but the lysate also con-tains broken pieces of chromosomal DNA (see Figure 7.10). If a
Can you devise an experimental strategy to get PI phage to trans duce the entire λ genome from one strain of bacterium to another strain? (The general features of phage lambda's reproductive cycle
Lets suppose a new strain of PI has been identified that packages larger pieces of the E. coli chromosome. This new P1 strain packages pieces of the E. coli chromosome that are 5 minutes long. If two
If two bacterial genes are 0.6 minutes apart on the bacterial chromosome, what frequency of cotransductants would you expect to observe in a P1 transduction experiment?
In an experiment involving P1 transduction, the cotransduction frequency was 0.53. How far apart are the two genes?
In a cotransformation experiment (see solved problem S4), DNA was isolated from a donor strain that was proA+ and srrC+ and sensitive to tetracycline. (The proA and strC genes confer the ability to
If you took a pipette tip and removed a phage plaque from a petri plate, what would it contain?
As shown in Figure 7.16, phages with rII mutations cannot produce plaques in E. coli K12(λ), but wild-type phages can. From an experimental point of view, explain why this observation is so
In the experimental strategy described in Figure 7.18, explain why it was necessary to dilute the phage preparation used to infect E. coli B so much more than the phage preparation used to infect E.
In the experiment of Figure 7.1, Joshua Lederberg and Edward Tatum could not discern whether met+ bio+ genetic material was transferred to the met- bio- thr+ leu+ thi+ strain or if thr+ leu+ thi+
A researcher has several different strains of T4 phage with single mutations in the same gene. In these strains, the mutations render the phage temperature-sensitive. This means that
Explain how a U-tube apparatus can distinguish between genetic transfer involving conjugation and genetic transfer involving transduction. Do you think a U-tube could be used to distinguish between
What is an interrupted mating experiment? What type of experimental information can be obtained from this type of study? Why is it necessary to interrupt mating?
In a conjugation experiment, what is meant by the time of entry? How is the time of entry determined experimentally?
In your laboratory, you have an F- strain of E. coli that is resistant to streptomycin and is unable to metabolize lactose, but it can metabolize glucose. Therefore, this strain can grow on a medium
As mentioned in solved problem S2, origins of transfer can be located in many different locations, and their direction of transfer can be clockwise or counterclockwise. Let's suppose a researcher
An Hfr strain that is hisE+ and pheA+ was mixed with a strain that is hisE- and pheA-. The conjugation was interrupted and the percentage of recombinants for each gene was determined by streaking on
Acridine orange is a chemical that inhibits the replication of F factor DNA but does not affect the replication of chromosomal DNA, even if the chromosomal DNA contains an Hfr. Let's suppose that you
Discuss the advantages of the genetic analysis of bacteria and bacteriophages. Make a list of the types of allelic differences among bacteria and phages that are suitable for genetic analyses.
Complementation occurs when two defective alleles in two different genes are found within the same organism and produce a normal phenotype. What other examples of complementation have we encountered
Which changes in chromosome structure cause a change in the total amount of genetic material, and which do not?
An individual has the following reciprocal translocation:What would be the outcome of alternate and adjacent-1 segregation?
A phenotypically normal individual has the following combinations of abnormal chromosomes: The normal chromosomes are shown on the left of each pair. Suggest a series of events (breaks,
Two phenotypically normal parents produce a phenotypically abnormal child in which chromosome 5 is missing part of its long arm but has a piece of chromosome 7 attached to it. The child also has one
With regard to the segregation of centromeres, why is adjacent-2 segregation less frequent than alternate or adjacent-1 segregation?
Which of the following types of chromosomal changes would you expect to have phenotypic consequences? Explain your choices. A.Pericentric inversion B.Reciprocal translocation C.Deletion D.Unbalanced
Explain why a translocation cross occurs during metaphase of meiosis I when a cell contains a reciprocal translocation.
A diploid fruit fly has eight chromosomes. How many total chromosomes would be found in the following flies? A. Tetraploid B. Trisomy 2 C. Monosomy 3 D. 3n E. An + 1
A person is born with one X chromosome, zero Y chromosomes, trisomy 21, and two copies of the other chromosomes. How many chromosomes does this person have altogether? Explain whether this person is
Two phenotypically unaffected parents produce two children with familial Down syndrome. With regard to chromosomes 14 and 21, what are the chromosomal compositions of the parents?
Explain why small deletions and duplications are less likely to have a detrimental effect on an individual's phenotype than large ones. If a small deletion within a single chromosome happens to have

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