PFA
1 Name / pledge: 1. Flower color in foxglove (Digitalis purpurea) is determined by alleles at two unlinked gene loci. Individuals who are homozygous or heterozygous for the dominant W allele always have white flowers. However, individuals who are ww homozygous recessive can have either dark purple or light purple flowers, depending on the alleles present at a second gene locus; at this second locus, the allele for dark purple (D) is dominant over the allele for light purple (d). A. A parental cross between a plant with white flowers and a plant with light purple flowers yields 52 offspring with white flowers, 25 offspring with dark purple flowers, and 27 offspring with light purple flowers. In the spaces below, indicate the genotypes that are possible for the parents and the F1 individuals, and briefly explain how you determined their genotypes (6 points). White parent Light purple parent White F1 Dark purple F1 Light purple F1 Explanation: B. Imagine allowing the white F1 plants to self-fertilize. What phenotypic outcome(s) would you expect in the F2 offspring? In the space below, briefly explain your expected phenotypic outcome(s) and use the embedded tables to produce complete Punnett squares to support your answer (4 points). exam continues on next page Page 2 2. A. The hellbender (Cryptobranchus alleganiensis) is a large aquatic salamander that is also known locally as either the “Allegheny alligator” or “snot otter.” Its haploid (n) number of chromosomes is 30. Consider a germ-line cell of this species before and during meiosis. Complete the chart below indicating how many chromosomes and chromatids an individual cell has at each of the stages (4 points). Phase # chromosomes # chromatids G1 phase 60 0 Metaphase I 30 60 Prophase II 30 30 Telophase II 30 30 B. A recent study of hellbender genomics published in 2019 shows that all genes found in the genome of male hellbenders are also present in female hellbenders. However, some genes found in females are absent in the genome of males. What does this result suggest about the sex-determination system of hellbenders (2 points)? 3. The figure at right shows the relationship between dietary fat intake and litter size (top panel) and mammary cancer risk (bottom panel) for female mice homozygous and heterozygous for two different alleles (G and G’) at a single gene locus. Study the figure carefully; what does it tell you about (a) pleiotropy, (b) gene interactions, and (c) dominance relationships involving the two alleles at this locus? Briefly explain, and be sure to address all three issues in your answer (4 points). exam continues on next page Page 3 4. A-C. The flowering plant Haplopappus gracilis (right) has an unusually small number of chromosomes; it has just two homologous pairs, making n = 2 (haploid) and 2n = 4 (diploid). The P locus is found on the larger of the two chromosomes, and the Y locus is found on the smaller chromosome. Consider a plant that is a double heterozygote, PpYy. The three diagrams below represent anaphase of individual cells of this plant in either mitosis, meiosis 1, or meiosis 2. Each black line represents a chromosome or a chromatid, and the white dot indicates the centromere. Letters represent alleles at the P and Y loci present on a particular chromosome or chromatid. Some of the portrayed allele arrangements may be possible for the F1s in the particular anaphase shown, but other portrayed allele arrangements may be impossible. Study each diagram carefully, then indicate by boldfacing the appropriate text (1) whether the diagram indicates an F1 cell in Mitosis, Meiosis 1, or Meiosis 2, (2) whether the allele arrangements shown are possible or impossible for the type of anaphase portrayed, and (3) briefly explain your answer (6 points). A Mitosis Meiosis 1 Meiosis 2 || Possible Impossible B Mitosis Meiosis 1 Meiosis 2 || Possible Impossible C Mitosis Meiosis 1 Meiosis 2 || Possible Impossible D. The figure at right shows the two homologous pairs during the G1 phase of the cell cycle; the maternal and paternal chromosomes are shown in red and light blue, respectively. This individual is heterozygous DdEeFf at three loci; the D and E loci are located 12cM apart on the larger of the two chromosomes, while the F locus is located on the smaller separate chromosome. In the space below, write the genotypes of all possible haploid gametes this individual could produce, and specify the frequency of each gamete type expressed as a percentage of all gametes (4 points). exam continues on next page Page 4 5. The human pedigree at right shows the inheritance pattern for a trait known to be an autosomal recessive. Black symbols indicate individuals showing the trait, circles indicate females, and squares males. What part of the pedigree is inconsistent with autosomal recessive inheritance, and what might explain that inconsistency? Briefly explain your proposed hypothesis (3 points). 6. Dutch women who were pregnant during the winter famine of 1944-45 (the “Dutch Hunger Winter” near the end of World War II) had children and grandchildren who were unusually small and prone to diabetes and obesity as adults. Based on what you have learned in Bio 221, propose a hypothesis that would explain this result and briefly explain your answer (3 points). 7. In certain breeds of house cats, females can be black, yellow, or a black-and-yellow mosaic called tortoise-shell (see image at right). However, males of these breeds can be either black or yellow but never tortoise-shell. For example, in parental crosses between yellow females and black males, all of the F1 female offspring are tortoise-shell, but all of the F1 males are yellow. A. Using the information provided above, propose a hypothesis that would explain why tortoise-shell coloration occurs only in females, and briefly explain. As part of your answer, please produce the Punnett square in the space provided for the cross described above (2 points). B.What would be the most accurate description of the dominance relationships among the alleles controlling coat color in these cats? Briefly explain (2 points). exam continues on next page Page 5 8. A recessive allele called “forked” ( f) found at a particular gene locus in Drosophila produces split bristles and hairs. Another recessive allele at a second gene locus, “outstretched” (o), results in wings being carried at right angles to the body. At a third gene locus, the recessive allele “garnet” (g) produces pink eyes in young flies. A wild-type female whose father showed the recessive phenotype for all three traits (forked, outstretched, garnet) is crossed with a wild-type male. The F1 data appear below: F1: Females: all wild type! Males: 431 wild type 426 forked, outstretched, garnet 60 forked 57 outstretched, garnet 13 outstretched 10 forked, garnet 2 garnet 1 forked, outstretched 1000 Total A. What evidence from the F1 indicates that these three loci are closely linked on the X chromosome? Briefly explain (2 points). B. Of these three gene loci on the X chromosome, which one is the one in the middle? Briefly explain how you made this determination (2 points). C. Estimate the map distance between the middle locus and the two outer loci, and please show your work (2 points). D. Note from the F1 data that there is exactly one male with the phenotype forked and outstretched. If you crossed this male with a true-breeding wild type female, what would be the linkage relationship of the alleles at the three loci on the two X chromosomes of the daughters produced by this cross? Use the two lines in the response box to represent the two X chromosomes and map the alleles present in the daughters to these chromosomes (2 points). —————————————————— —————————————————— E. Now take one of the daughters of the cross described in part D and cross her with a wild-type male. What phenotypes are possible in the male offspring, and what frequency (percentage of all male offspring) would you expect to find for each phenotype (2 points)? Make sure that your answer focuses just on the male offspring. You are done with the exam!