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Question: A recessive allele in mice results in

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 necks. Crosses were made between these two populations to produce an F1 generation of mice with normal necks. The F1 mice were then mated to each other to obtain an F2 generation. For the mice that were born alive, the following data were obtained:
522 mice with normal necks
62 mice with long necks
What percentage of homozygous mice (that would have had long necks if they had survived) died during embryonic development?

> 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

> 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 a

> 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.

> 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

> In a cotransformation experiment (see question 4 of More Genetic TIPS), DNA was isolated from a donor strain that was proA+ and strC+ and sensitive to tetracycline. (The proA and strC genes confer the ability to synthesize proline and confer streptomycin

> In a cotransduction experiment using P1, the transfer of one gene is selected for and the presence of the second gene is then determined. If 0 out of 1000 transductants that carry the first gene also carry the second gene, what would you conclude about t

> In a cotransduction experiment involving P1, the cotransduction frequency was 0.53. How far apart are the two genes?

> If two bacterial genes are 0.6 minute apart on the bacterial chromosome, what cotransduction frequency would you expect to observe in a cotransduction experiment using P1 phage?

> Let’s suppose a new strain of P1 phage has been identified that packages larger pieces of the E. coli chromosome. This P1 strain packages pieces of the E. coli chromosome that are 5 minutes long. If two genes are 0.7 minute apart along the E. coli chromo

> Can you devise an experimental strategy to get a P1 phage to transduce the entire genome of a λ (lambda) phage from one strain of bacterium to another strain? (Note: The general features of the reproductive cycle of λ phage are described in Chapter 18.)

> In a P1 transduction experiment, the P1 lysate contains phages that carry pieces of the host chromosomal DNA, but the lysate also contains broken pieces of chromosomal DNA (see Figure 7.10). If a P1 lysate is used to transfer chromosomal DNA to another b

> In Chapter 23, the technique of fluorescence in situ hybridization (FISH) is described. This is another method for examining sequence complexity within a genome. In this method, a DNA sequence, such as a particular gene sequence, can be detected within a

> What causes the cleavage furrow in an animal cell to ingress?

> Although 61 codons specify the 20 amino acids, most species display a codon bias. This means that certain codons are used much more frequently than other codons. For example, UUA, UUG, CUU, CUC, CUA, and CUG all specify leucine. In yeast, however, the UU

> The protein known as tyrosinase is needed to make certain types of pigments. Tyrosinase is composed of a single polypeptide with 511 amino acids. The molecular mass of this protein is approximately 61,300 Da, or 61.3 kDa. People who carry two defective c

> The technique of Western blotting is described in Chapter 21 and also in experimental question E5. Let’s suppose a researcher is interested in the effects of mutations on the expression of a proteinencoding gene that encodes a protein we will call protei

> Chapter 21 describes a blotting method known as Western blotting that can be used to detect the production of a polypeptide that is translated from a particular mRNA. In this method, a protein is detected with an antibody that specifically recognizes and

> Describe the structure of a polysome, which is depicted in Figure 13.13a. From Figure 13.13a: Ribosome Polypeptide MRNA 0.1 um H

> Discuss how the elucidation of the structure of the ribosome can help us to understand its function.

> Polypeptides can be translated in vitro. Would a bacterial mRNA be translated in vitro by eukaryotic ribosomes? Would a eukaryotic mRNA be translated in vitro by bacterial ribosomes? Why or why not?

> In the experiment of Figure 13.7, what would be the predicted amounts of amino acids incorporated into polypeptides if the RNA was a random polymer containing 50% C and 50% G? From Figure 13.7: Experimental level Conceptual level 1. Place the cell

> When a chi square analysis is applied to solve a linkage problem, explain why an independent assortment hypothesis is proposed.

> Describe the unique features of ascomycetes that lend themselves to genetic analysis.

> During which phase are sister chromatids separated and sent to opposite poles?

> 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. Let’s suppose that two genes, gene A and gene B, are 5,000,000 bp apart on the same c

> 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

> 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?

> Though we often think of genes in terms of the phenotypes they produce (e.g., curly leaves, flaky tail, brown eyes), the molecular function of most genes is to encode proteins. Many cellular proteins function as enzymes. The following table gives the map

> 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 of the F1 offspring had brown fur and long tails. The F1 offspring were crossed to mice with white fur and short ta

> 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 have also examined the blood types of individu

> What is the difference in meaning between the terms genetic recombination and crossing over?

> As described in Chapter 22, 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

> Explain why maternal effect genes exert their effects during the early stages of development.

> Suppose that a gene affects the anterior morphology in house flies and is inherited as a maternal effect gene. The gene exists in a functional allele, H, and a recessive nonfunctional allele, h, which causes a small head. A female fly with a normal head

> Where are the two ends of a kinetochore microtubule?

> Suppose a maternal effect gene exists as a functional dominant allele and a nonfunctional recessive allele. A mother who is phenotypically abnormal produces all normal offspring. Explain the genotype of the mother.

> For Mendelian inheritance, the nuclear genotype (i.e., the alleles found on chromosomes in the cell nucleus) directly influences an offspring’s traits. In contrast, for non-Mendelian inheritance patterns, the offspring’s phenotype cannot be reliably pred

> A Drosophila embryo dies during early embryogenesis due to a recessive maternal effect allele called bicoid−. The wild-type allele is designated bicoid+. What are the genotypes and phenotypes of the embryo’s mother and maternal grandparents?

> A maternal effect gene exists in a dominant N (functional) allele and a recessive n (nonfunctional) allele. What would be the ratios of genotypes and phenotypes for the offspring of the following crosses? A. nn female × NN male B. NN female × nn male

> Describe the inheritance pattern of maternal effect genes. Explain how the maternal effect occurs at the cellular level. What are the expected functional roles of the proteins that are encoded by maternal effect genes?

> How many Barr bodies would you expect to find in humans with the following abnormal compositions of sex chromosomes? A. XXY B. XYY C. XXX D. X0 (a person with just a single X chromosome)

> On rare occasions, a human male is born who is somewhat feminized compared with other males. Microscopic examination of the cells of one such individual revealed that he has a single Barr body in each cell. What is the chromosomal composition of this ind

> Describe the molecular process of X-chromosome inactivation. This description should include the three phases of inactivation and the role of the Xic. Explain what happens to the X chromosomes during embryogenesis, in adult somatic cells, and during ooge

> Describe when X-chromosome inactivation occurs and how this leads to phenotypic results at the organism level. In your answer, you should explain why XCI causes results such as variegated coat patterns in mammals. Why do two different calico cats have th

> Among different species, describe three distinct mechanisms for accomplishing dosage compensation.

> What is the difference between homologs and sister chromatids?

> What is a Barr body? How is its structure different from that of other chromosomes in the cell? How does the structure of a Barr body affect the level of X-linked gene expression?

> With regard to the numbers of sex chromosomes, explain why dosage compensation is necessary.


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