Let’s suppose you were looking through a vial of fruit flies in your laboratory and noticed a male fly with pink eyes. What crosses would you make to determine if the pink allele is an X-linked gene? What crosses would you make to determine if the pink allele is an allele of the same X-linked gene that occurs as a white allele?
> Describe the steps you would take to produce a tetraploid plant from a diploid plant.
> Describe how colchicine can be used to alter chromosome number.
> With regard to the analysis of chromosome structure, explain the experimental advantage that polytene chromosomes offer. Discuss why changes in chromosome structure are more easily detected in polytene chromosomes than in ordinary chromosomes.
> Let’s suppose a researcher conducted comparative genomic hybridization (see Figure 8.9) and accidentally added twice as much DNA from normal cells (labeled with red fluorescence) relative to DNA from cancer cells. What ratio of green-to-red fluorescence
> What is the main goal of comparative genome hybridization? Explain how the ratio of green to red fluorescence provides information about chromosome structure.
> 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 lacke
> As mentioned in question 2 of More Genetic TIPS, 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 H
> 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 g
> In a conjugation experiment, what is meant by the time of entry? How is the time of entry determined experimentally?
> Which individual(s) in this pedigree exhibit(s) the effect of incomplete penetrance?
> 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?
> 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?
> In the experiment of Figure 7.1, Lederberg and 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
> In the experiment of Figure 7.1, a met− bio− thr+ leu+ thi+ cell could become met+ bio+ thr+ leu+ thi+ by a (rare) double mutation that converts the met− bio− genes into met+ bio+. L
> 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 heterozygote
> 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 testcrossed to aabb individuals. A. If the testcross produces 1000
> In Morgan’s three-factor crosses 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. From Figure 6
> 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?
> 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
> In your own words, explain why a testcross cannot produce more than 50% recombinant offspring. When a testcross does produce 50% recombinant offspring, what does this result mean?
> Does a PP individual produce more of the protein encoded by the P gene than is necessary for the purple color?
> 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
> In the experiment of Figure 6.6, Stern followed the inheritance pattern in which females carried two abnormal X chromosomes to correlate genetic recombination with the physical exchange of chromosome pieces. Is it necessary to use a strain carrying two a
> 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
> 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 whi
> 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
> 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 pro
> 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 F1 offspring had green pods and normal leaves. The F1 p
> 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 oblate (flattened) shape. A plant that is true-br
> Two genes in tomatoes are 61 mu apart; normal fruit (F) is dominant to fasciated (flattened) fruit ( f ), and normal number of leaves (Lf ) is dominant to leafy (lf ). A true-breeding plant with normal leaves and fruit was crossed to a leafy plant with f
> 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. From Figure 6.1:
> Why do you think the heterozygote offspring of two Manx cats survives with developmental abnormalities, whereas the homozygote dies?
> 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? F
> 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.
> 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 o
> 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 gen
> 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 sna
> As a hypothetical example, a trait in mice results in abnormally 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-breedin
> Chapter 21 describes two blotting methods (i.e., Northern blotting and Western blotting) used to detect gene products. Northern blotting detects RNA and Western blotting detects proteins. Suppose that a female fruit fly is heterozygous for a maternal eff
> Describe three advantages of using pea plants as an experimental organism.
> Pick any trait you like in any species of wild plant or animal. The trait must somehow vary among different members of the species (see Figure 1.7). Note: When picking a trait to answer this question, do not pick the trait of wing color in butterflies.
> 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.
> What is the molecular explanation for sex-limited inheritance?
> Many organisms are studied by geneticists. Do you think each of the following species would be more likely to be studied by a transmission geneticist, a molecular geneticist, or a population geneticist? Explain your answer. Note: More than one answer may
> Figure 1.5 shows a micrograph of chromosomes from a normal human cell. If you created this kind of image using a cell from a person with Down syndrome, what would you expect to see? From Figure 1.5: 10 20 21 22 BNG ( e PEGE 4
> The technique known as DNA sequencing (described in Chapter 21) enables researchers to determine the DNA sequence of genes. Would this technique be used primarily by transmission geneticists, molecular geneticists, or population geneticists?
> What is a genetic cross?
> A cross was made between two strains of plants that are agriculturally important. One strain was disease-resistant but herbicide-sensitive; the other strain was disease-sensitive but herbicide-resistant. A plant breeder crossed the two plants and then al
> When examining a human pedigree, what features do you look for to distinguish between X-linked recessive inheritance and autosomal recessive inheritance? How would you distinguish X-linked dominant inheritance from autosomal dominant inheritance in a hum
> As mentioned in Experimental Question E11, red eyes is the wildtype phenotype. Several different genes (with each gene existing in two or more alleles) are known to affect eye color. One allele causes purple eyes, and a different allele causes sepia eyes
> A variegated trait in plants is analyzed using reciprocal crosses. The following results are obtained: Variegated female x Normal male Normal female x Variegated male 1024 variegated + 52 normal 1113 normal + 61 variegated Explain this pattern of inh
> Chapter 21 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 c
> What is the phenotype of a female cow that is heterozygous?
> Explain how the use of radiolabeled amino acids in this procedure helped to reveal the genetic code.
> 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. From Figure 5.1: Parental generation DD d dd DD F, generation Dd Dd All dextral All sinistral F2 gen
> Summer squash exist in long, spherical, or disk shapes. When a true-breeding long-shaped strain was crossed to a true-breeding disk-shaped strain, all of the F1 offspring were disk-shaped. When the F1 offspring were allowed to self-fertilize, the F2 gene
> As shown in Figure 4.17, coat color in rodents is governed by a gene interaction. An albino rat is crossed to a black rat. The ratio of their offspring is 1 agouti : 1 black : 2 albino. What are the genotypes of the parents? From Figure 4.17: AaCc x
> Duroc Jersey pigs are typically red, but a sandy variation is also seen. When two different varieties of true-breeding sandy pigs were crossed to each other, they produced F1 offspring that were red. When these F1 offspring were crossed to each other, th
> The Mic2 gene in humans is present on both the X and Y chromosome. Let’s suppose the Mic2 gene exists in a dominant Mic2 allele, which results in normal surface antigen production, and a recessive mic2 allele, which results in defective surface antigen p
> In the clover butterfly, males are always yellow, but females can be yellow or white. In females, white is a dominant allele. Two yellow butterflies were crossed to yield an F1 generation consisting of 50% yellow males, 25% yellow females, and 25% white
> A particular breed of dog can have long hair or short hair. When true-breeding long-haired animals were crossed to true-breeding short-haired animals, the offspring all had long hair. The F2 generation showed a 3:1 ratio of long- to short-haired offsprin
> In sheep, the formation of horns is a sex-influenced trait; the allele that results in horns is dominant in males and recessive in females. Females must be homozygous for the horned allele to have horns. A horned ram was crossed to a polled (unhorned) ew
> In chickens, some varieties have feathered shanks (legs), but others do not. In a cross between a Black Langhans (feathered shanks) and a Buff Rocks (unfeathered shanks), the shanks of the F1 generation are all feathered. When members of the F1 generatio
> Red eyes is the wild-type phenotype in Drosophila, and several different genes (with each gene existing in two or more alleles) affect eye color. One allele causes purple eyes, and a different allele causes vermilion eyes. The purple and vermilion allele
> Why are the homologous regions of the X and Y chromosome important during meiosis?
> In a species of plant, two genes control flower color. The red allele (R) is dominant to the white allele (r); the color-producing allele (C) is dominant to the non-color-producing allele (c). You suspect that either an rr homozygote or a cc homozygote w
> Mexican hairless dogs have little hair and few teeth. When a Mexican hairless is mated to another breed of dog, about half of the puppies are hairless. When two Mexican hairless dogs are mated to each other, about 1/3 of the surviving puppies have hair a
> A rare form of dwarfism that also included hearing loss was found to run in a particular family. It is inherited as a dominant trait. It was discovered that an affected individual had one normal copy of chromosome 15 and one abnormal copy of chromosome 1
> White-eyed flies have a lower survival rate than red-eyed flies. Based on the data in Figure 3.18, what percentage of white-eyed flies survived compared with red-eyed flies, assuming 100% survival of red-eyed flies? From Figure 3.18: Experimental le
> With regard to thickness and length, what do you think chromosomes would look like if you microscopically examined them during interphase? How would that compare with their appearance during metaphase?
> Let’s suppose that you have made a karyotype of a female fruit fly with red eyes and found that it has three X chromosomes instead of the normal two. Although you do not know its parents, you do know that this fly came from a mixed cult
> Occasionally during meiosis, a mistake can happen whereby a gamete may receive zero or two sex chromosomes rather than one. Bridges made a cross between white-eyed female flies and red-eyed male flies. As you would expect, most of the offspring were red-
> How would you set up crosses to determine if a gene is Y-linked versus X-linked?
> In his original studies of Figure 3.18, Morgan first suggested that the original white-eyed male had two copies of the white-eye allele. In this problem, let’s assume that he meant the fly was Xw Yw instead of Xw Y. Are his data in Figu
> In Morgan’s experiments, which result do you think is the most convincing piece of evidence pointing to X-linkage of the eye color gene? Explain your answer.
> Explain why the reciprocal cross yields a different result from the first cross.
> A tall pea plant with axial flowers was crossed to a dwarf plant with terminal flowers. Tallness and axial flowers are dominant traits. The following offspring were obtained: 27 tall, axial flowers; 23 tall, terminal flowers; 28 dwarf, axial flowers; and
> Let’s suppose you conducted an experiment involving genetic crosses and calculated a chi square value of 1.005. There were four categories of offspring (i.e., the degrees of freedom equaled 3). Explain what the 1.005 value means. Your answer should inclu
> Experimentally, how do you think researchers were able to determine that the Y chromosome causes maleness in mammals, whereas the ratio of X chromosomes to the sets of autosomes causes sex determination in fruit flies?
> Female flies with white eyes and miniature wings (both X-linked recessive traits) were crossed to male flies with red eyes and long wings. On rare occasions, female offspring were produced with white eyes. If we assume these females are due to errors in
> Discuss why crosses (i.e., the experiments of Mendel) and the microscopic observations of chromosomes during mitosis and meiosis were both needed to deduce the chromosome theory of inheritance.
> When studying living cells in a laboratory, researchers sometimes use drugs as a way to cause cells to remain in a particular phase of the cell cycle. For example, aphidicolin inhibits DNA synthesis in eukaryotic cells and causes them to remain in the G1
> Would it be possible to deduce the law of independent assortment from a single-factor cross? Explain your answer.
> For Mendel’s data for the experiment in Figure 2.8, conduct a chi square analysis to determine if the data agree with Mendel’s law of independent assortment. From Figure 2.8: Experimental level Conceptual level Tr
> The fungus Melampsora lini causes a disease known as flax rust. Different strains of M. lini cause varying degrees of the rust disease. Conversely, different strains of flax are resistant or sensitive to the various varieties of rust. The Bombay variety
> As in many animals, albino coat color is a recessive trait in guinea pigs. Researchers removed the ovaries from an albino female guinea pig and then transplanted ovaries from a true-breeding black guinea pig. They then mated this albino female (with the
> What features of this pedigree indicate that the allele for Duchenne muscular dystrophy is X-linked? From Figure 4.10: -Unaffected, presumed heterozygote I-1 I-2 Affected with DMD II-1 II-2 II-3 II-4 II-5 Il-6 III-1 III-2 III-3 III-4 III-5 III-6 II
> From the point of view of crosses and data collection, what are the experimental differences between a single-factor and a two-factor cross?
> For all seven characters described in the data of Figure 2.5, Mendel allowed the F2 plants to self-fertilize. He found that when F2 plants with recessive traits were crossed to each other, they always bred true. However, when F2 plants with dominant trai
> How long did it take Mendel to complete the experiment in Figure 2.5? From Figure 2.5: Experimental level Conceptual level 1. For each of seven characters, Mendel P plants TT x cross-fertilized two different true- breeding strains. Keep in mind that
> Explain the technical differences between a cross-fertilization experiment versus a self-fertilization experiment.
> The data with Figure 2.5 show the results of the F2 generation for seven of Mendel’s experiments. Conduct a chi square analysis to determine if these data are consistent with the law of segregation.
> A recessive allele in mice results in an unusally long neck. Sometimes, during early embryonic development, the long neck causes the embryo to die. An experimenter began with a population of true-breeding normal mice and true-breeding mice with long neck
> In fruit flies, curved wings are recessive to straight wings, and ebony body is recessive to gray body. A cross was made between true-breeding flies with curved wings and gray bodies and flies with straight wings and ebony bodies. The F1 offspring were t
> The alleles his-5 and lys-1, found in baker’s 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-1 and his+ lys+. From the analysis of 818 tetrads, the
> Let’s 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 re
> 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 that is AA bb CC was crossed to an individual that is aa
> Why are both of these colors considered to be wild type?
> 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
> 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 a pintail were cro
