遗传学双语课练习题资料.docx

1、遗传学双语课练习题资料 Medialian genetics1 Shown are F2 results of two of Mendels monohybrid crosses. State a null hypothesis that you will test using chi-square analysis. Calculate the x2 value and determine the p value for both crosses, then interpret the p values. Which cross shows a greater amount of devia

2、tion? (a)Full pods 882 Constricted pods 299 (b)Violet flowers 705 White flowers2242 In Dmsophihla, gay body color is dominant over ebony body color, while long wings are dominant over vestigial wings. Work the following crosses through thee F2 generation, and determine the genotypic and phenotypic r

3、atios for each generation. Assume that the Pl individuals are homozygous: (a)gray, long ebony, vestigial (b) gray, vestigial ebony, long (c) gray, long gray, vestigial3.How many different types of gametes can be formed by individuals of the following genotypes? What are they in each case? (a) AaBb,(

4、b) AaBB, (c)AaBbCc, (d)AaBBcc, (e)AaBbcc and (f) AaBbCcDdEe?4.Using the forked-line method, detennine thee genotypic and phenotypic ratios of these trihybrid crosses:(a)AaBbCcAaBBCC, (b)AaBBCcaaBBCc, and (c) AaBbCc AaBbCc.5. Mendel crossed peas with round, green seeds with peas having wrinkled, yell

5、ow seeds. All Fl plants had seeds that were round and yellow-Predict the results of test crossing these F1 plants.6. In one of Mendels dihybrid crosses, he observed 315 round, yel low; 108 round,green; 101 wrinkled, yellow; and 32wrinkled, green F2 plants. Analyze these data using chi-square analysi

6、s to see whether (a) they fit a 9:3:3:1 ratio; (b)the round, wrinkled trait fit for a 3:1 ratio; or (c) the yellow, green traits fit a 3:1ratio.7. A geneticist, in assessing data that fell into two phenotypic classes, observed values of 250:150. He decided to perform chi-square analysis using two di

7、fferent null hypotheses: (a) The data fit a 3:1 ratio; and (b) the data fit a l:1 ratio.Calculate the X2 values for each hypothesis-What can you conclude about each hypothesis?8. The basis for rejecting any null hypothesis is arbitrary. The researcher can set more or less stringent standards by deci

8、ding to raise or lower the critical p value. Would the use of a standard of p=0.10 be more or less stringent in failing to reject the null hypothesis? Explain.9. Consider three independently assorting gene pairs, A/a, B/b, and C/c, where each demonstrates typical dominance (A-, B-, C- ), and recessi

9、veness (aa, bb, cc). What is the probability of obtaining offspring that is AABbCc from parents that are AaBbCC and AABbCc?10. What is the probability of obtaining a triply recessive individual from thee parent as shown in Problem 9?11. Of all offspring of the Parents in Problem 9, what proportion w

10、ill express all three dominant traits?12. For the following pedigree, predict the mode of inheritance and the resulting genotypes of each individual. Assume that the alleles A and a control the expression of the trait.13. Which of Mendels postulates are demonstrated by the pedigree in Problem 12? Li

11、st and define these postulates.14. The following pedigree follows the inheritance of myopia (near-sightedness) in humans. Predict whether the disorder is identified as a dominant or a recessive trait. Based on your predic6on, indicate the most probable genotype for each individual.15. Two true-breed

12、ing pea plants are crossed. One parent is round, terminal, violet, constricted, while the other expresses the contrasting phenotypes of wdnkled, axial, white, full. The four pairs of contrasting traits are controlled by four genes, each located on a separate chromosome. In the F1 generation only rou

13、nd, axial, violet, and full are expressed. In the F2 generation, all possible combinations of these traits are expressed in ratios consistent with Mendelian inheritance.(a) What conclusion can you draw about the inheritance of these traits based on the Fl results?(b) Which phenotype appears most fre

14、quently in the F2 results? Write a mathematical expression that predicts the frequency of occurrence of this phenotype.(c) Which F2 phenotype is expected to occur 1east frequently? Write a mathematical expression that predicts this frequency.(d) How often is either Pl phenotype likely to occur in th

15、e F2 generation?(e) If the Fl plant is testcrossed, how many different phenotypes will be produced, and how does this number compare to the number of different phenotypes in the F2 generation discussed in part (b)?16. Tay-Sachs disease (TSD) is an inborn error of metabolism that results in death, us

16、ual1y before the age of five. You are a genetic counselor, and you interview a phenotypically normal couple who consult you because the man had a female first cousin (on Ms fathers side) who died tom TSD, and the woman had a maternal uncle with TSD. There are no other known cases in either family, a

17、nd none of the matings were/are between related individuals. Assume that this trait is rare in this population.(a)Using standard pedigree symbols, draw a pedigree of these individuals, families, showing the relevant individuals.(b)The couple asks you to calculate the probability that they both are h

18、eterozygous for the TSD allele.(c)They also want to know the probability that neither of them is heterozygous.(d)They also ask you for the probability that one of them is heterozygous but the other is not.Hint: thee answers to (b), (c), and(d) should add up to1.0.17 Chlamydomonas, a eukaryotic green

19、 alga, is sensitive to the antibiotic erythromycin, which inhibits protein synthesis in prokaryotes. There are two mating types in this alga, mt+ and mt-, If an mt+ cell sensitive to the antibiotic is crossed with an mt- cell that is resistant, all progeny cells are sensitive. The reciprocal cross (

20、mt+ resistant and mt- sensitive) yields all resistant progeny cells. Assuming that the mutation for resistance is in the chloroplast DNA, what can you conclude from the results from these crosses?sex determination1. As related to sex determination, what is meant by (a) homomorphic and heteromorphic

21、chromosomes; (b) isogamous and heterogamous organisms?2. Contrast the life cycle of a plant such as zea mays with an animal such as C.elegans-.3. Discuss the role of sexual differentiation in the life cycles of chlamydomonas, ZE mays, and C .elegans. 4. Distinguish between the concepts of sexual dif

22、ferentiation and sex detem1ination.5. Contrast the Protenor and Lygaeus modes of sex determination.6. Describe the major difference between sex determination in Drosophila and in humans.7. What specific observations (evidence) support the conclusions you have drawn about sex determination in Drosoph

23、ila and humans?8. Describe how nondisjunction in human female gametes can give rise to Klinefelter and Turner syndrome offspring following fertilization by a normal male gamete.9. An insect species is discovered in which the heterogametic sex is unknown. An X-linked recessive mutation for reduced wi

24、ng (rw) is discovered. Contrast the F1 and F2 generations from a cross between a female with reduced wings and a male with normal sized wings when (a)the female is the heterogametic sex; (b) the male is the heterogametic sex.10. Based on your answers in boblem9, is it possible to distinguish between

25、 Protenor and Lygaeus mode of sex determination based on the outcome of these crosses?11.When COWS have twin calves of unlike sex (fraternal twins), the female twin is usually sterile and has masculinind reproductive organs. This calf is referred to as a freemartin .In cows, twins may share a common

26、 placenta and thus fetal circulation. Predict why a freemartin develops.12. It has been suggested that any male-determining genes contained on the Y chromosome in humans cannot be located in the limited region that synapses with the X chromosome during meiosis. What might be the outcome if such gene

27、s were located in this region?13. What is a Barr body, and where is it found in a cell? 14. Indicate the expect ed number of Barr bodies in interphase cell of the following individuals; KIinefelter syndrome; Tumer syndrome; and karyotypes 47,XYY, 47,XXX, and 48,XXXX.15. Define the Lyon hypothesis.16

28、 .Can the Lyon hypothesis be tested in a human female who is homozygous for one allele of the X-linked G6PD gene? Why, or why not?17. Predict the potential effect of the Lyon hypothesis on the region of a human female heterozygous for the X-linked red-green color blindness trait.18. Cat breeders are

29、 aware that kittens expressing the X-linked calico coat pattern and tortoise shell pattern are almost invariable females. Why?19. What does the apparent need for dosage compensation mechanisms suggest about the expression of genetic information in normal diploid individuals?Linkage and Chromosome Ma

30、pping in eukaryotyes1. What is the significance of crossing over (which leads to genetic recombination to the process of evolution?2. Describe the cytological observation that suggests that crossing over occurs during the first meiotic prophase.3. Why does more crossing over occur between two distan

31、tly linked genes than between two genes that aree very close together on the same chromosome?4. Why is a 50 percent recovery of single-crossover products the upper limit, even when crossing over always occurs between two linked genes?5. Why are double-crossover events expected less frequently than s

32、ingle-crossover events? 6. What is the proposed basis for positive interference? 7. What three essential criteria must be met in order to execute a successful mapping cross?8. The genes dumpy wings ( dp ),clot eyes (cl), and apterous wings (ap) are linked on chromosome II of Drosophilia .in a series of two-point mapping crosses, the genetic distances shown below were determined-What is the sequence of the three genes? dp-ap 42 dp-cl 3 ap-cl 399. Consider two hypothetical recessive autosomal genes a and b, where a heterozygote is