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Genetics Analysis And Principles 5th Edition Robert Brooker - Solutions
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 head. A female fly with a normal head is mated to a true-breeding male with a small head. All of the
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 to maternal effect genes, would the phenotype of such a cloned animal be determined by the animal
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 cells is detected as a band on a gel. If one type of cell produces twice as much of a particular
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 + 52 normal 1113 normal + 61 variegated Explain this pattern of inheritance.
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 consistent with her hypothesis.
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 blotting detects RNA, and Western blotting detects proteins. Suppose that a female fruit fly is
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 following types of crosses: Cross 1: When true-breeding females with normal tails are crossed to
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. How would you determine the genotype of this female snail? In your answer, describe your expected
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. Therefore, you conclude that you are not certain of the genotype of this male snail. On a different
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 results of gel electrophoresis for a heterozygous female of the following species?A. MarsupialB.
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 was known to be homozygous for the normal Igf2 allele. Male B was from a litter of eight mice that
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 initial sample of tissue produce both forms of G-6-PD?
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 cannot be used to produce a strain of heterozygous flies that could be used in future studies. How
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 cells, these bacteria were free-living organisms. However, we cannot take a mitochondrion or chloroplast
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 disorder and, within the same pedigree, also examined the individuals with regard to their blood types.
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 were crossed to mice with white fur and short tails. What are the possible phenotypes of the F2
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 interference affect these theoretical values?
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. How does the inability to detect double crossovers affect the calculation of map distance? Is map
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, gene A and gene B, are 5,000,000 bp apart on the same chromosome. Genes A and B are in a hot spot for
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 pigmentation (A) dominant to albino (a); the other gene affects hair length, with long hair (L)
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 the outcome of this single crossover event? If a second crossover occurs somewhere between A and C,
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. In your own words, explain how this analogy also applies to the idea that the likelihood of crossing
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 explained by independent assortment.
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 aabb individuals. A. If this cross produces 1000 offspring, what are the predicted numbers of
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 individuals were crossed to each other. The F1 heterozygotes were then testcrossed to 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 leaves and fruit was crossed to a leafy plant with fasciated fruit. The F1 offspring were then
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 dominant to flattened, or oblate shape. A plant that is true-breeding for the dominant traits was crossed
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 Ft offspring had green pods and normal leaves. The F, plants were then crossed to plants with yellow
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 defective inosine triphosphatase gene that does not produce any of this enzyme and is also
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 dominant to narrow). Both genes are located on chromosome 5. A third gene, located on chromosome 4,
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 female with a bushy tail and yellow fur was crossed to a white male without a bushy tail (i.e., a normal
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 recessive to normal. A true-breeding normal plant with green pods and green seedlings was crossed
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 gait. Jerker mice with a snubnose and pintail were crossed to normal mice, and then the F1 mice were
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 third gene is 18.5 mu away from the vestigial wings allele and 6 mu away from the allele causing purple
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 who is AA bb CC was crossed to an individual who is aa BB cc to produce heterozygous F1 offspring.
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, gene L exists in a dominant, normal allele and in a recessive allele, l that is lethal. Heterozygous
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 and his* lys'. From the analysis of 818 individual tetrads, the following numbers of tetrads were
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 that crossing over can explain the recombination of alleles of dif¬ferent genes, how would you modify
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 chromosome? Explain.
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 dominant alleles be linked on the same chromosome and all of the recessive alleles be linked on 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 recombinant offspring an underestimate or overestimate of the actual map distance?
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 how he determined this.
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 tail. A recessive allele that causes a jerker (uncoordinated) phenotype is located on chromosome 4.
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 differences among these processes.
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 chromosomal DNA is not random (i.e., it is more likely to break at certain spots as opposed to other
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 cell's chromosome. This means that bacteria have evolved molecular mechanisms for the purpose of
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 why certain bacteria make antibiotics is to kill other species that occupy the same environment.
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 bacteriophage T4 have a mutation in the rIIA gene that gives a rapid-lysis phenotype, yet they never
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- cells? Explain your answer.
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 strains of E. coli have pili on their cell surface. These pili enable E. coli to conjugate with other
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 I'I lysate is used to transfer chromosomal DNA to another bacterium, how could you show experimentally
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 are described in Chapter 17.) Phage λ has a genome size of 48,502 nucleotides (about 1% of the size
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 genes are 0.7 minutes apart along the E. coli chromosome, what would be the cotransduction
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 synthesize proline and confer streptomycin resistance, respectively.) A recipient strain is proA- and
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 significant.
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. coli K 12(λ).
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+ genetic material was transferred to the met+ bio+ thr- leu- thi- strain. Let's suppose that one strain
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 temperature-sensitive phages can propagate when the bacterium (E. coli) is grown at 32°C but cannot propagate
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 transduction and transformation?
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 that contains glucose and streptomycin, but it cannot grow on a medium containing lactose. A
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 conjugated six different Hfr strains that were thr+ leu+ tons strr azis lac+ gal+ pro+ met+ to an F-
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 a medium that lacked either histidine or phenylalanine. The following results were obtained:A.
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 have an E. coli strain that is unable to metabolize lactose and has an F factor that carries a
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 in previous chapters of this textbook?
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, translocations, crossovers, etc.) that may have produced this combination of chromosomes.
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 normal copy of chromosome 5 and two normal copies of chromosome 7. With regard to chromosomes 5 and
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 translocation
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 euploid or aneuploid.
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 a phenotypic effect, what would you conclude about the genes in this region?
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