Molecular Genetics 501 Chapter 10 Practice Problems1Practice Problems 41. The diploid chromosome number in a variety of chrysanthemum is 18. Whatwould you call varieties with the following chromosome numbers?(a) 19 (b) 36 (c) 17 2. A normal chromosome has the following gene sequence: A B C!D E F G H.Write the name of each of the following kinds of chromosomal mutation:(a) A B C F E D G H (b) A B D E F C G H (C) A B D E F G H 3. Draw diagrams showing the appearance of synapsed chromosomes inprophase of meiosis I, in cells that are heterozygous for (a) a deletion; (b) aduplication; (c) an inversion; and (e) a reciprocal translocation.4. Imagine a cross between two species of plants, where the hybrid is sterile forthe same reason that you found above for mules. Now suppose that in the germline of the plant, there is a breakdown in the mechanism controlling the cell cyclein a cell, such that the cell goes through two consecutive S phases without anyintervening mitosis. What will be the chromosome composition of themicrospore or megaspore mother cell(s) which are eventually formed? (Assumethe same simple model of chromosomes as in the preceding question.)5. DNA molecules can be denatured or "melted" by heating them until all H-bonds break. When they are cooled, the single strands renature or reanneal, i.e.complementary regions re-form H-bonds to create double-stranded DNAmolecules again. Suppose that you isolated DNA from two strains of a virus.The DNA of these two strains differ only in that a particular gene is duplicated inone strain. These DNA's are mixed and then denatured and renatured. If youexamine the resulting molecules in the electron microscope, what would theylook like?6. Suppose a transposable element inserted itself, or a copy of itself: (a) with theportion of a gene that codes for a protein; or (b) immediately upstream from agene. What do you predict would be the effect on that gene?7. What would be the ploidy of the zygote that results from each of the followingevents?(a) An egg is fertilized by two sperm instead of one.(b) A cell in the germ line begins mitosis but fails to undergo anaphase, so all thechromosomes end up in one nucleus. A descendent of this cell undergoesmeiosis and the resulting egg is fertilized.Molecular Genetics 501 Chapter 11 Practice Problems2(c) A secondary spermatocyte fails to undergo the second meiotic division. Oneof the resulting sperm fertilizes an egg.(d) The second polar body nucleus fuses with the egg nucleus; then the egg isfertilized.8. Diagram the results of the following types of cross-overs. In each casecarefully draw the chromosome(s) with homologous regions paired and trace thechromosome(s) from one end, e.g. the centromere (shown as a circle on the leftend).(a) Intrachromosomal crossing-over between direct repeats:o 1 2 3 1 2 3 (b) Unequal sister-strand exchange (crossing-over) involving tandem repeats:o 1 2 3 1 2 3 o X 1 2 3 1 2 3(c) Intrachromosomal crossing-over between inverted repeats:o 1 2 3 a b c 3 2 1 (d) Crossing-over between repeats on different chromosomes:o 1 2 3 o 1 2 3 9. This illustrates how trisomics can be used to determine on which chromosomea gene lies. In heterozygous trisomics, the alleles on the three copies of thetrisomic chromosome segregate randomly with respect to genotype, in thefollowing proportions:Thus the final proportions of gametes produced by a trisomic A A a organismwill be 1/6 A A, 2/6 A a, 2/6 A, and 1/6 a.In maize, the su locus is on chromosome VI; the mutant allele causes theendosperm to be sugary. Suppose you cross a homozygous Su plant to ahomozygous su plant and then textcross the trisomic F1. What phenotypic ratiosMolecular Genetics 501 Chapter 11 Practice Problems3will be seen in the testcross progeny if the P1 Su plant is (a) trisomic forchromosome VI; and (b) trisomic for another chromosome, e.g. V?Molecular Genetics 501 Chapter 11 Practice Problems410. Three point mutants (a, b and c) were tested for complementation with the 5deletion mutants (D1 through D5) diagrammed below. The data obtained fromcomplementation tests is given in the table (+ = complementation; 0 = nocomplementation).Show the approximate locations of the point mutations a, b and c on theline labeled "MAP".Δ1 Δ2 Δ3 Δ4 Δ5 MAP Deletions1 2 3 4 5a o + o o +b o + + + oc o + + o +11. Suppose you are doing genetics with maize and are trying to locate the genepr (red endosperm). You have a strain of maize of genotype pr pr and in whichboth copies of chromosomes 9 have knobs (karyotype 9k 9k). You cross this witha strain of genotype Pr Pr in which neither chromosome 9 has a knob (9 9). TheF1 is testcrossed to a knobless pr pr strain. The numbers and phenotypes of thetestcross progeny are as follows:pr pr 9k 9 46pr pr 9 9 3Pr pr 9 9 45Pr pr 9k 9 5Is the pr locus on chromosome 9? In a sentence or two, explain how you can tell.12. In her studies of yeast genetics, Janet isolated 5 adenine auxotroph mutants:ade1, ade2, ade3, ade4, ade5. She did some crosses to get each one in mating type aand α. Then she mated them in all pairwise combinations and tested theresulting diploids for their ability to grow on medium without adenine. Resultsare shown below, where “yes” means that the diploid can grow without adenineand “no” means it cannot.ade1ade2ade3ade4ade5Molecular Genetics 501 Chapter 11 Practice Problems5ade1nonoyesyesyesade2 noyesyesyesade3 noyesnoade4 noyesade5 no(a) How many complementation groups did she find, and what mutants are ineach group?(b) How many different genes are represented in her collection of five mutants?(c) Are ade1 and ade2 alleles? Are ade1 and ade3