医学遗传学：anwsers of Exercise_1(1)

1、Exercise 1TRUE/FALSE 1. _T_ An autosomal（常染色的） locus with 8 alleles has 28 heterozygotes（杂合体）.(a1,a2,a3,a4,a5,a6,a7,a8; 7+6+5+4+3+2+1=28)2._F_ The more the chromosome interference the more recombination frequency underestimates map distance.(the more the chromosome interference the less recombinatio

2、n frequency ,so we can derive from it a shorter map distance )3. _F_ In meiosis, there are two chromosome replications and one cell division.(one chromosome replication two cell divisions)VOCABULARY1. _ zygotene _ The meiotic prophase stage in which the homologous chromosomes synapse(联会).2. _anaphas

3、eThe mitotic phase directly following metaphase（中期）.3. _6_ The variance of a c2 distribution with 3 degrees of freedom.4. _female_ The sex of an XXY Drosophila（果蝇）（A ratio）5. _testcross_ A mating of type AaBbCc x aabbcc6. _narrow heritability_The additive genetic variance divided by the total phenot

4、ypic variance.7. _autosome_The chromosomes other than the sex chromosomesMULTIPLE CHOICE & SHORT PROBLEMS1. How many kinds of gametes can be produced by an individual of genotype!AABbccDdEeFfGgHH?A. 2B. 8C. 16D. 32E. 642. Given a mating of type Aa x aa, what is the probability that a family of 5 chi

5、ldren includes at least onehomozygote?A.15/16B. 2/3C. 7/8D. 31/32E. 1/2 (1-(0.5)5)=31/323. The P value associated with a test statistic like X2 isA. The Pr that the null hypothesis is falseB. The Pr that the null hypothesis is trueC. One minus the probability that the null hypothesis is more likely

6、than the alternativeD. The Pr of obtaining an X2 value at least as deviant as that observed if the hypothesis is falseE. The Pr of obtaining a result at least as far from expected as observed if the hypothesis is true4. Mrs. Smith has two brothers with hemophilia. What is the Pr that Mrs. Smiths nex

7、t child will be ahemophiliac if it is a boy? A. 1/2B. 1/3C. 1/4D. 1/5E. 1/6（1/2*1/2）5. Mendel crossed plants with white flowers with plants with violet flowers and got all violet flowers in the F1.In the F2 he got 224 white and 705 violet flowers. Test his hypothesis. What, approximately, is X2?A. 0

8、.28B. 0.39C. 0.06D. 0.67E. 0.556. What phenotypic ratio would you expect from the testcross of an F1, that gives a 9:7 ratio in the F2?A. 1:3B. 2:1C. 15:1D. 1:1:1:1E. 1:2:1 7. What is the most likely mode of inheritance of this disease?A. autsomal dominantB. autosomal recessiveC. holandric（伴雄遗传）D. X

9、-linked recessiveE. X-linked dominantPROBLEMS 1. Peas heterozygous for three independently assorting loci are intercrossed, i.e., AaBbCc x AaBbCc.Of the offspring,A. What proportion will be homozygous for all three recessive alleles? _1/64_B. What proportion will be homozygous at all three loci? _1/

10、8_C. What proportion will be homozygous for one locus and heterozygous for the other two? _3/8_D. What proportion will be homozygous for the recessive allele of at least one locus? _37/64_2. In the plant called Shepards Purse we saw in lecture and in the text that the mating between two true breedin

11、g strains, one with triangular seeds and the other with oval seeds, produces plants with triangular seeds in the F1 and that when the F1 is selfed the F2 gives a 15:1 ratio of triangular to oval seed plants. The two loci, in that example, were unlinked. Suppose that the two loci had been linked with

12、 a recombination frequency of 0.2.a. What F2 ratio would you expect?b. What proportion of the F2 is expected to be homozygous for both dominant alleles?a. we can know from the narration that only when homozygous for the two recessive alleles exist , the phenotype is oval. so when we take recombinati

13、on frequency into account , the ratio is (1-0.8*0.8*0.25):0.8*0.8*0.25=21:4b.4/25Exercise 2 What is the principle of segregation, and how is this principle demonstrated in the results of a single-gene (monohybrid) cross?Mendels first law, the principle of segregation, states that the two members of

14、a gene pair (alleles) segregate (separate) from each other in the formation of gametes; half the gametes carry one allele, and the other half carry the other allele.If the parents are heterozygous, then F1s phenotype ratio is 3:1 What is the principle of independent assortment, and how is this princ

15、iple demonstrated in the results of a two-gene (dihybrid) cross?Mendels second law, the principle of independent assortment, states that genes for different traits assort independently of one another in gamete production.If the parents are heterozygous, then F1s phenotype ratio is 9:3:3:1 Explain wh

16、y random union of male and female gametes is necessary for Mendelian segregation and independent assortment to be observed in the progeny of a cross.When two pairs of alleles show independent assortment, under what conditions will a 9 : 3 : 3 : 1 ratio of phenotypes in the F2 generation not be obser

17、ved?When the duplicate gene or the cooperation of a regulatory and a regulated gene or the interference between genes exist will a 9 : 3 : 3 : 1 ratio of phenotypes in the F2 generation not be observed Explain the following statement: “Among the F2 progeny of a dihybrid cross, the ratio of genotypes

18、 is 1: 2 : 1, but among the progeny that express the dominant phenotype, the ratio of genotypes is 1 : 2.”It is the result of a single-gene (monohybrid) cross.11. The pattern of coat coloration in dogs is determined by the alleles of a single gene, with S (solid) being dominant over s (spotted). Bla

19、ck coat color is determined by the dominant allele A of a second gene, tan by homozygosity for the recessive allele a. A female having a solid tan coat is mated with a male having a solid black coat and produces a litter of six pups. The phenotypes of the pups are 2 solid tan, 2 solid black, 1 spott

20、ed tan, and 1 spotted black. What are the genotypes of the parents?Ssaa SsAa12. In the human pedigree shown here, the daughter indicated by the red circle (II-1) has a form of deafness determined by a recessive allele. What is the probability that the phenotypically normal son (II-3) is heterozygous

21、 for the gene?2/313. Huntington disease is a rare neurodegenerative human disease determined by a dominant allele, HD. The disorder is usually manifested after the age of forty-five.A young man has learned that his father has developed the disease.(a) What is the probability that the young man will

22、later develop the disorder? 3/4(b) What is the probability that a child of the young man carries the HD allele? 3/816. Red kernel color in wheat results from the presence of at least one dominant allele of each of two independently segregating genes (in other words, R- B- genotypes have red kernels). Kernels on rr bb plants are white, and the genotypes R- bb and rr B- result in brown kernel color. Suppose that plants of a variety that is true breeding for red kernels are crossed with plants true breedin