PRACTICE PROBLEMS 11. The diagram shows the nucleus of a diploid cell in G2. In this organism, N = 2;chromosome 1 is metacentric with a knob near the end; and chromosome 2 isacrocentric with no knob. Numbers 1-8 refer to centromeres.(a) A line and the letters en represent the location of two copies of the en gene; drawanother line with en to indicate the location of the other two copies.(b) Draw two arrows labelled sc pointing to any one pair of sister chromatids.(c) Draw two arrows labelled hc pointing to any one pair of homologouschromosomes.(d) Which centromere(s) will segregate from the following centromeres at mitosis?1 2 3 4 (e) Which centromere(s) will segregate from the following centromeres at meiosis I?5 6 7 8 2. The diagram below depicts a microspore mother cell of maize in anaphase of meiosisI, except that the chromosomes are missing. The maize plant is heterozygous at the Clocus on chromosome 9 and and the P locus on chromosome 10: C c P p––––o–––– ––––o–––– ––––o– ––––o– chromosome 9 chromosome 10Draw the chromosomes, chromatids, and marker genes in the diagram below, attachedto the chromosome fibers, assuming that this particular meiosis is going to producefour pollen grains with the indicated genotypes.3. An organism that is heterozygous for one gene produces two different genotypes ofgametes; if heterozygous for two genes, four different genotypes can be produced.How many different genotypes would you expect could be produced by an individualheterozygous for three genes? Four genes? Is there a general formula for n genes?4. Recall that in peas, Y and y determine yellow and green peas, respectively, and T andt determine tall and short plants. A plant of genotype Y y T t is crossed to a short plantthat developed from green seeds.(a) What is this kind of cross called? (b) Out of 100 progeny seeds, how many do you expect to be yellow?(c) Out of 100 progeny seeds, how many do you expect to be green and produceshort plants?5. Write the genotypes of all of the genetically different pure lines that can be obtainedby inbreeding mice whose genotype is a a B b C c.6. In guinea pigs, rough coat (R) is dominant over smooth coat (r). A rough coatedguinea pig is bred to a smooth coated one, producing 8 rough and 7 smooth progeny.Write the genotypes of the parents, and the genotypes and ratios of the offspring:Parents: X Offspring: 7. Recall that two independently-segregating genes in maize determine plant height(tall, T vs. short, t) and leaf posture (relaxed, R vs. upright, r). Two pure lines withphenotypes tall relaxed and short upright are crossed.(a) Write the genotypes of the parents: X (b) Two F1 individuals from this cross are themselves crossed to each other to producean F2 generation. Use probability theory to calculate the proportion of the F2individuals that will be tall and upright, and can produce both tall and short offspring ifthey are selfed.(c) Suppose that you looked at only 16 progeny from the cross in (b). Set up thebinomial theorem to calculate the probability that you would get exactly the expectedproportion that you calculated in (b). (you don't have to do the actual arithmetic, justshow the equation with the appropriate numbers in it).8. A couple wants to have three children. The wife wants to have at least one girl,while the husband wants at least one boy. What is the probability that they will gettheir wish?9. A naive geneticist has two Drosophila, male and female, both heterozygous for blackbody color b+b (wild type is grey and dominant). He wants to get homozygousrecessive flies to use in test crosses. He mates the two heterozygotes and throws awayall but 8 eggs, claiming that he will get one female b b and one male b b from these eggs.(a) What is the probability that he will get exactly this?(b) What is the probability that he will be disappointed and fail to get at least one male bb and at least one female b b?10. Albinism in humans is due to a single recessive gene. A number of two-child familieswith normal parents are selected on the basis that they have produced at least onealbino child. In what proportion of these families would you expect to find that theother child is also albino?11. From a cross of peas of genotypes R r X r r, two samples are taken of different sizes.In each case, the observed values differ from the expected by the same proportion (7/3= 70/30). Calculate Chi-square values and the associated probabilities for each, anddecide if you would accept or reject the hypothesis of ordinary Mendelian segregation.Note the effect of sample size!(a) N = 10 Observed = 7 round, 3 wrinkled(b) N = 100 Observed = 70 round, 30 wrinkled12 What is the ratio of phenotypes and genotypes expected in the progeny of a crossbetween two organisms heterozygous for the same lethal