Zoo/Bot 3333 Genetics Quiz #3 3/25/11 For answers to the quiz, click here: 1. A 40 year old woman gives birth to an infant with Down Syndrome. The number of Barr bodies you would expect to see in a dividing cell at metaphase from this baby is: a) none; b) one; c) two; d) three; e) it would depend on the sex of the infant. 2. A chromosome has the following array, where banded regions are represented by letters and numbers and the ‘dot’ represents the centromere: MAPLE.SUG4R. If all breakage events occurred between functional transcription units, and position effect was not observed, which of the following chromosome breakage and restitution events is most likely to result in lethality to an individual carrying a copy of this chromosome? a) MLPAE.SUG4R; b) MAPUS.ELG4R; c) MAPLE.SUR; d) both a and b; e) all are equally likely to result in lethality. 3. True or false. One way that inversions may be generated is through intrachromosomal recombination. Questions 4-5 pertain to the following: The following gene loci are found on chromosome nine in corn: c......bz....wx.....sh..........d.....centromere 12 8 10 20 10 Phenotype Number Colored, green, starchy, smooth, tall 350 Where C = colored; c = white; Bz = green leaves; White, bronze, waxy, shrunk, dwarf 355 bz = bronze leaves; Wx= starchy seeds; wx = Colored, bronze, waxy, shrunk, dwarf 50 waxy seeds; Sh = smooth seeds, sh = shrunken White, green, starchy, smooth, tall 46 seeds; D = tall plants; d = dwarf plants. Colored, green, starchy, smooth, dwarf 85 A plant from a standard genetic stock that is White, bronze, waxy, shrunk, tall 84 homozygous for the five recessive alleles is Colored, bronze, waxy, shrunk, tall 8 crossed to a naturally growing plant from Mexico White, green, starchy, smooth, dwarf 9 that is homozygous for all five dominant alleles. Colored, green, waxy, smooth, tall 7 The F1 plants express all dominant traits, and White, bronze, starchy, shrunk, dwarf 6 when backcrossed to the homozygous recessive parents, produce the following progeny phenotypes in the frequencies indicated in the table on the right: 4. How many phenotypic progeny classes are expected in this cross? a) 8; b) 10; c) 16; d) 18; e) 32. 5. Which of the following provides an explanation for the above results? a) the parent plant mutant for these genes carries a deletion for these five loci; b) these results are due to a translocation moving the shrunken and dwarf loci to another chromosome; c) these results are due to an inversion moving the d gene locus to the other side of the centromere; d) the distance between the colored and bronzed loci is significantly different in the wild strain relative to the standard strain; e) none of the above. 6. The RNAs that mediate RNA interference: a) are trans-acting; b) are single-stranded; c) can be derived from the introns of protein-coding genes; d) all of the above; e) none of the above. Questions 7-8 pertain to the following: In tomatoes, J.W. Lesley determined the location of several gene loci by selffertilizing three different plants, each trisomic for a different chromosome (A, B, or I) carrying a dominant allele and heterozygous for the following allele pairs on the other homologs: 7. On the basis of this data, the allele pairs which are on chromosome I are: a) Dd; b) Dd, Ll, Rr and Aa; c) Yy and Rr; d) Rr; e) none of the above. 8. On the basis of this data, the genotype of the trisomic B parent was: a) AaDdLlYyRr; b) AAaDDdLlYyRrr; c) AaDdLLlYyRr; d) AAaDDdLLlYyyRRr; e) AaaDddLllYyRrr. Questions 9-10 pertain to the following deletion mapping problem (see Hartwell discussion of deletion mapping, pp. 496-498 . In the midge, eight genes (a,b,c,d,e,f,g, and h) are linked together on one chromosome, but their order is unknown. Six overlapping deletions are found to reveal (‘uncover’) recessive alleles of the genes as follows: Deletion 1: uncovers a, b, c, and e. Deletion 2: uncovers a, c, and d. Deletion 3: uncovers c and e Deletion 4: uncovers a and c. Deletion 6: uncovers d, f, and h. Deletion 7: uncovers f and g. 9. True or false: gene c lies between a and e. 10. True or false: From the information given, it cannot be determined whether gene g or gene f is next to gene h.