Question 1___________________________ Question 2___________________________ Question 3 ___________________________ TotalAverage = 44 out of 50 points Important – please keep your answers short; confine your answers to the space provided; do not write on the back of any pages ! PCB5065 Fall Exam 4 - ChaseName Key page 1 of 4

1 (21 pt) In your own words, define or describe each of the following: 1-a) Hetroplasmy (as it pertains to organelle genetics) More than one organelle genotype in a cell or individual or organelle Not accepted: More than one organelle genome in a cell or individual or organelle - because there are always multiple organelle genomes 1-b) Meiotic drive Events in meiosis or subsequent gametogenesis that favor the transmission of one allele or genotype over another Not accepted: Events in meiosis or subsequent gametogenesis that favor the transmission of one gene over another 1-c) Maternal effect gene Gene expressed such that the genotype of the mother determines the phenotype of the progeny 1-d) Epigenetics Heritable changes in gene expression that do not involve changes in the DNA sequence 1-e) Genomic imprinting Parent of origin differences in gene expression such that only the paternal or maternal allele is expressed 1-f) Paramutation Changes in the expression of an allele directed by association with another allele 1-g) Gametophytic effect in plants Technically fits the definition of meiotic drive so that definition was accepted or Transmission bias resulting from the effects of gene expression on the function of the haploid gametophyte PCB5065 Fall 2012 Exam 4 ChaseName __________________________________ page 2 of 4

2. (15 pt) In the human pedigree shown above, shaded individuals are affected by vision loss in young adulthood. Squares represent males and circles females. Roman numerals indicate generations and Arabic numerals indicate individuals. 2-a) Based upon the pedigree shown, could this vision-loss trait be the result of a recessive nuclear autosomal mutation? Explain why or why not. Technically yes, if you assume that unaffected mates are carriers. If you said no because it would be unusual to have so many carriers, I accepted that, although this would obviously depend on allele frequencies in the population, etc. If you said no because there were not Mendelian progeny ratios you did not get full credit, because these are very small families, so Mendelian ratios are not necessarily expected. (Remember, flipping the coin six times, you don’t necessarily get 3 heads and 3 tails. 3-b) Based upon the pedigree shown, could this vision-loss trait be the result of a genetic mutation in a maternal effect gene? Explain why or why not. No. In a maternal effect, all the progeny of a single maternal parent will have the same phenotype. That is not the case here. 3-c) Based upon the pedigree shown, could this vision-loss trait be due to a mitochondrial gene mutation? Explain why or why not. Yes. The trait appears to be passed from mother to offspring. Considering that mitochondrial mutations can condition vision loss and that affected mothers can be heteroplasmic for such mutations, variably affected progeny are to be expected. In reality, this pedigree is from a family segregating for a mitochondrial mutation that conditions Leber’s hereditary optic neuropathy (Wallace et al. Science 242:1427) PCB5065 Fall 2012 Exam 4 ChaseName __________________________________ page 3 of 4

3 (15 pt) The diagram illustrates the expression patterns of an imprinted gene region in mammals. The insulin growth factor 2 (Igf2) gene is an imprinted gene. The paternal allele is expressed and the maternal allele is silenced. In mice, loss of Igf2 function leads to a small, but viable, mouse. 3-a) If a female mouse is heterozygous for a loss-of-function mutation at the Igf2 locus (genotype Igf2 -/+), will this mouse have a mutant or wild-type phenotype? Explain your answer. This depends on whether the female mouse in question inherited the mutant or wild-type allele from her father; the paternally inherited copy is expressed, so if dad contributed the mutant allele, the mouse in question is mutant; if dad contributed the wild-type allele, the mouse in question is wildtype 3-b) If the Igf2 -/+ female mouse is mated with a wild-type (Igf2 +/+) male mouse, what are the expected progeny genotypes and phenotypes? Explain your answer. 3-c) If an Igf2 +/+ female mouse is mated with an Igf2-/+ male mouse, what are the expected progeny genotypes and phenotypes? Explain your answer. enhancers PCB5065 Fall 2012 Exam 4 ChaseName __________________________________ page 4 of 4 [from Munshi and Duvvuri J Genet Genom 434:93] ♀ genotype ♂ genotypeexpected progeny genotypesexpected progeny phenotypes + / +Igf2 - / +50% + / + 50% Igf2 - / + 50% normal mouse because the paternal + allele was transmitted & expressed 50% small mouse because the paternal mutant allele was transmitted & expressed ♀ genotype ♂ genotypeexpected progeny genotypesexpected progeny phenotypes Igf2 - /++ / +50% + / + 50% Igf2 - / + 100% normal because only the paternally transmitted allele is expressed and all paternal alleles are + in this cross