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Unformatted text preview: Chapter 5 REVIEW QUESTIONS 1. A linkage group a. Can occur only on an autosome b. Is a collection of genes that never produce recombinant gametes c.Is a chromosomal region in which crossing over cannot occur d. Represents all of the genes located on the same chromosome 2. When Morgan carried out crosses involving two X-linked genes in Drosophila , he sometimes observed new phenotypes that were not present in the parents. From these observations, he proposed that a. There are two copies of each X chromosome gene present in females and only one copy of the X chromosome gene in males. b. Genes that are located close together on a chromosome are more likely to be separated during gamete formation. c.The points of overlap between synapsed homologous chromosomes, called chiasmata, were points of genetic exchange. d. The mechanism for gene separation must take place in mitosis. 3. True or false? Genes on the same chromosome that are more than 50 map units apart are too far apart to produce crossover gametes. 4. The frequency of crossover between genes A and B is 7.5%, between genes B and C is 34.5%, and between genes A and C is 41.4%. What is the most likely order of these three genes? a. A B C b. C A B c.B C A d. The gene order cannot be determined from these data. 5. How can the order of three linked genes (A, B, and C) on the same chromosome be determined? a. Look for double crossover phenotypes involving the wild-type and mutant alleles of genes A, B, and C. b. Look for single crossover phenotypes involving the wild-type and mutant alleles of genes A, B, and C. c.Look for parental phenotypes. d. Gene order cannot be determined by looking at the results of a cross. 6. When analyzing three genes that reside on the same chromosome, the expected frequency of double-crossover events can be determined by multiplying the frequency of single crossovers between each pair of genes. What would cause the number of observed double-crossover events to be less than the expected value? a. The Poisson distribution b. The coefficient of coincidence ( C ) c.Negative interference d. Positive interference 7. Why do mapping experiments become less accurate when the distances between genes become large? a. Crossover gametes become less common. b. Recombination occurs less frequently in long chromosomes. c.Interference is greater when the distance between genes is large....
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This note was uploaded on 04/04/2008 for the course BIO 2204 taught by Professor Athwal/haines during the Spring '08 term at Temple.
- Spring '08