* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Name: ______/40 points TF:
Survey
Document related concepts
Y chromosome wikipedia , lookup
Minimal genome wikipedia , lookup
Designer baby wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Point mutation wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Microevolution wikipedia , lookup
Neocentromere wikipedia , lookup
Genome (book) wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Transcript
Name: ____________________________________________ TF: _____________/40 points ____________________________________________ Collaborators (if applicable): _________________________________________________________________________ Life Sciences 1b Problem Set 3 Due in TF dropbox (Science Center 2nd floor), Monday Feb 22 at 12:00pm. 1. (5 points) The African pygmy hedgehog, Atelerix albiventris, has a diploid chromosome number of 90, including one pair of sex chromosomes. A. How many chromosomes would you expect to find in a pygmy hedgehog somatic cell during metaphase of mitosis? How many chromatids? Would the chromatids be identical? Explain your reasoning. B. How many chromosomes would you expect to find in a pygmy hedgehog somatic cell during anaphase of mitosis? How many chromatids? Explain your reasoning. C. How many chromosomes would you expect to find in a pygmy hedgehog germ cell during metaphase of meiosis I? How many chromatids? Would the chromatids be identical? Explain your reasoning. D. How many chromosomes would you expect to find in a pygmy hedgehog germ cell during metaphase of meiosis II? Explain your reasoning. 2. (6 points) Methotrexate is a drug that can inhibit cell division by preventing the synthesis of purine bases. Cells treated with methotrexate arrest at a particular stage of the cell cycle. A. During which stage of the cell cycle would you expect cells treated with methotrexate to arrest? Briefly explain. Below are histograms (graphs) showing the numbers of cells containing different amounts of DNA in three different samples: cells treated with two different drugs (A and B), and cells that have not been treated with a drug. The untreated cells are progressing through the cell cycle at a normal rate, while the cells that have been treated with drugs tend to arrest at different stages in the cell cycle. Treated with Drug A # of cells # of cells Untreated cells x 2x DNA content Treated with Drug B # of cells B. x 2x DNA content x 2x DNA content On the histogram of “untreated cells” indicate which bars in the graph represent cells in each of the following stages of the cell cycle: G1, S, and G2. If there are bars that you cannot assign to one of these stages, do not label them. C. Would you expect cells treated with methotrexate to produce results more similar to those shown for Drug A or Drug B? Briefly explain your reasoning, including how the data in the graph is consistent with the effect of methotrexate on cell cycle progression. D. Which of the following drugs could be drug B? Briefly explain your reasoning for each. • Vinblastine, which binds to tubulin and inhibits microtubule assembly • PPMP, a cytokinesis inhibitor 3. (8 points) A particular species of scorpion has two pairs of homologous chromosomes, and shown below are the karyotypes of a normal male and a normal female scorpion as well as selected offspring from a mating between them. The larger chromosome is chromosome I, and the smaller chromosome is chromosome II. Remember that karyotypes are made using metaphase chromosomes, so each chromosome shown contains two sister chromatids, though they cannot be distinguished from one another, as they are held together tightly. Karyotype of female parent: Karyotypes of selected offspring: 1 2 3 Karyotype of male parent: 4 5 A. For this species of scorpions, n = __________ and 2n = __________ B. For each of the offspring (1-5), identify whether the karyotype is normal or if there is an abnormality. If there is an abnormality, identify the abnormality (e.g., monosomy chr. II), and in which parent and which phase of meiosis (I or II, or either) the error could have occurred. Offspring Normal (yes/no)? Abnormality (if applicable) Parent and phase of meiosis (I or II) in which abnormality occurred (if applicable) 1 2 3 4 5 C. Generally, offspring with chromosomal abnormalities such as these are not viable – they die early in development. Individuals with some chromosomal abnormalities, however, are able to survive. What factor determines the extent of the defect caused by a particular chromosomal abnormality (i.e., why are humans with trisomy 21 sometimes able to survive, while individuals with trisomy 1 are not)? Why is this factor so important? 4. (8 points) In plants, the NBS-LRR genes mediate disease resistance. Many of these genes have highly similar sequences and are located adjacent to one another in the genome. To study them, you have chosen the model plant Arabidopsis thaliana, which is easy to grow and manipulate in the lab. Consider the following cluster of NBS-LRR genes from a specific locus in Arabidopsis thaliana. There are six NBS-LRR genes at this site in the genome (NBS-LRRA – NBS-LRRF), and the diagram below shows their relative positions on the homologous chromosomes of an individual who is heterozygous for all six genes (NBS-LRRA/NBS-LRRa, NBS-LRRB/NBS-LRRb, etc.). NBS-LRRA NBS-LRRB NBS-LRRC NBS-LRRD NBS-LRRE NBS-LRRF NBS-LRRa NBS-LRRb NBS-LRRc NBS-LRRd NBS-LRRe NBS-LRRf Below are the genotypes of three gametes produced by this individual. Some of the gametes have missing or extra NBS-LRR genes due to unequal crossing over during meiosis. For each gamete shown (I) determine between which genes the crossover occurred on each chromosome and (II) write out the genotypes of the other three products of meiosis. In the genotypes, you do not need to write out the “constant” part of the gene name (NBS-LRR), only the final identifying letter (A or a, B or b, etc.) A. NBS-LRRa B. NBS-LRRa NBS-LRRb NBS-LRRc NBS-LRRd NBS-LRRF C. NBS-LRRA NBS-LRRB NBS-LRRc NBS-LRRd NBS-LRRe D. NBS-LRRb NBS-LRRc NBS-LRRd NBS-LRRD NBS-LRRE NBS-LRRF NBS-LRRf Which of the gametes from A, B, and C would you predict would produce a next-generation individual with reduced resistance to disease as a result of the loss of one or more NBS-LRR genes? A: ____________________________________________ B: ____________________________________________ C: ____________________________________________ NBS-LRRC 5. (9 points) You are interested in behavioral genetics, and have selected zebrafish as your model system. You are studying how quickly fish respond to a flash of light, and have identified several mutants that respond more slowly than wild-type fish. You take three females who exhibit this delayed-response phenotype, and cross each with a homozygous wild-type male. In the progeny, you observe the following numbers of normal and slow-responding offspring: # of normal offspring # of offspring with delayed response phenotype Cross 1 21 32 Cross 2 42 0 Cross 3 0 37 A. For each cross, identify whether the mutant phenotype is dominant or recessive, and the genotype of the female from the cross. Define any symbols that you use. B. Do you think that the mutation in the female from cross 1 is more likely to be a loss of function mutation or a gain of function mutation? What about cross 2? Briefly explain how you came to each decision in the space provided. C. You decide to study one of these mutations further by making a transgene that contains the mutation using the strategy discussed in class (inject a plasmid containing the transgene into 1celled embryos). For this purpose, you select a dominant mutation. Why is it necessary for the mutation to be dominant in order for this strategy to work? D. If you cross two of the offspring from cross 3 with each other, what proportion of individuals in the next generation would you expect to display the delayed-response phenotype? Show your work or explain your reasoning. 6. (4 points) Cystic fibrosis is inherited in an autosomal recessive manner. An unaffected male has two children with an unaffected female. One of their children, Chen is unaffected by the disease; the other child, Chao, has cystic fibrosis A. What is the genotype of Chen and Chao’s mother? Briefly explain your answer. B. What is the probability that Chen is a carrier for cystic fibrosis? Show your work or explain your reasoning? C. Chen has a child with an unaffected female named Lin. Lin has an affected brother, but neither of her parents are affected. What is the probability that Chen and Lin’s child will be an unaffected girl? Show your work or explain your reasoning.