Chapter 3 Review Genetics

Chapter 3 Review 1. Name the single individual whose work in the mid-1800s contributed to our understanding of the particulate nature of inheritance as well as the basic genetic transmission patterns. With which organism did this person work? Gregor Mendel; Pisum sativum 2. A recessive allele in tigers causes the white tiger. If two normally pigmented tigers are mated and produce a white offspring, what percentage of their remaining offspring would be expected to have normal pigmentation? 75% 3. Which types of phenotypic ratios are likely to occur in crosses when dealing with a single gene pair for which all the genotypic combinations are of equal viability? 1:2:1, 3:1 4. The fundamental Mendelian process that involves the separation of contrasting genetic elements at the same locus is called ________. Segregation 5. Mendel's unit factors in pairs are most accurately known to be __________. two alleles on paternal and maternal homologs 6. True or False: 1:1 phenotypic ratio is expected from a monohybrid cross involving a heterozygote with a homozygous recessive organism. True 7. How could the botanist best determine whether the genotype of the green-pod plant is homozygous or heterozygous? Cross the green-pod plant with a yellow-pod plant. 8. Punnett squares can be used to predict the two possible outcomes of the botanist’s test cross. The Punnett square on the left shows the predicted result if the unknown plant is homozygous (GG); the Punnett square on the right shows the predicted result if the unknown plant is heterozygous (Gg). 9. Suppose that the botanist carried out the test cross described in Parts A and B and determined that the original green-pod plant was heterozygous (Gg). Which of Mendel’s findings does her test cross illustrate? Law of Segregation 10. During which part of meiosis (meiosis I or meiosis II) do the two alleles of a gene separate? During which phase does the separation occur? (Assume no recombination.) Meiosis 1, Anaphase 11. True or False: A 9:3:3:1 phenotypic ratio is expected from a dihybrid cross between a double heterozygote and a fully recessive organism. False 12. Which of the following phenomena is a consequence of Independent Assortment? The phenotypic ratio among phenotypes produced from an F1 X F1 dihybrid cross is 9:3:3:1 13. The 9:3:3:1 ratio exhibited in the F2 generation of a dihybrid cross is a genotypic ratio. False 14. A pea plant is heterozygous for two genes; one controlling height, one controlling color. The genotype is written PpTt. Based on the Law of Independent Assortment, approximately what proportion of the pollen produced by this plant should have the genotype PT? ¼ 15. 16. 17. 18. Assuming independent assortment, what proportion of the offspring of the cross AaBbCcDd X AabbCCdd will have the aabbccdd genotype? Zero 19. The nonfunctional form of a gene is called a wild-type allele. False 20. How did Mendel's work support the chromosomal theory of inheritance? The behavior of chromosomes during meiosis, as observed under a microscope, correlated with Mendel's principles of inheritance. 21. For what purpose should the product law be applied? To calculate the probability of two or more independent events occurring simultaneously. 22. Assume that a Chi-square test was conducted to test the goodness of fit to a 9:3:3:1 ratio and a Chi-square value of 10.62 was obtained. Should the null hypothesis be accepted? No 23. Assume that a Chi-square test provided a probability value of 0.02. Should the null hypothesis be accepted? No 24. The Chi-square test involves a statistical comparison between measured (observed) and predicted (expected) values. One generally determines degrees of freedom as ________. one less than the number of classes being compared 25. You would like to know whether the progeny of a pair of mated fruit flies are distributed among the resulting four phenotypic classes in a 1:1:1:1 ratio. You perform a chi-square test and obtain a p value of 0.04. Assuming you have done the test correctly, select the best interpretation of this result. The differences between the observed and expected counts are too large to be attributed to chance. 26. The larger the number of total individual counts in a chi-square test, the higher the degrees of freedom (df). False 27. The expected ratio of phenotypes among the progeny of a test cross is 1:1:1:1. Out of 200 total resulting progeny, 48 occur in one of the four phenotypic classes. Given this information, which of the following must also be true? The value of observed - expected for this cell = -2 28. What information can be obtained from a human pedigree? Pedigree analysis can help determine how a trait is inherited. 29. In a cross between a black and a white guinea pig, all members of the F1 generation are black. The F2 generation is made up of approximately ¾ black and ¼ white guinea pigs. 30. What will the offspring be like if two F2 white guinea pigs are mated? All white 31. Two different matings were made between black members of the F2 generation with the following results. 32. Which of Mendel's postulates can only be demonstrated in crosses involving at least two pairs of traits? Independent Assortment 33. Distinguish between homozygosity and heterozygosity. 34. Identify each mutation as either dominant or recessive. Straight is dominant to curled and short is dominant to long. 35. Assign gene symbols and, for each cross, determine the genotypes of the parents. Possible symbols would be (using standard Drosophila symbolism): straight wings = w + curled wings = w short bristles = B + long bristles = B 36. A gain-of-function mutation __________. results in an increased quantity of the normal gene product 37. Assume that a cross is made between two organisms that are both heterozygous for a gene that shows incomplete dominance. What phenotypic and genotypic ratios are expected in the offspring? 1:2:1 38. What is the difference between incomplete dominance and codominance? In codominance, both phenotypes are expressed in heterozygotes. In incomplete dominance, the heterozygote shows a phenotype that is intermediate between the two homozygote 39. The presence of more than two alternative forms of a given gene would be called ________. Multiple Alleles 40. In a mating between individuals with the genotypes IAIO X IOIO , what percentage of the offspring are expected to have the O blood type? 50% 41. If the green allele is designated as G, and the aurea allele is designated as GA , assign genotypes to the phenotypes listed. 42. How can the unusual results from the crosses be explained? The aurea allele behaves as a recessive lethal allele. 43. With respect to snapdragon color, what can be said of the G and GA alleles? The GA is dominant to the G allele. 44. How many tall plants with violet flowers were expected? 90 45. How many tall plants with white flowers were expected? 30 46. How many dwarf plants with violet flowers were expected? 30 47. How many dwarf plants with white flowers were expected? 10 48. Use a chi-square analysis to test the hypothesis that the F2 data for stem length (tall:dwarf) is consistent with Mendel's law of segregation. 0.53 49. Can the deviation of observed values from expected values be attributed to random chance? Yes 50. Use a chi-square analysis to test the hypothesis that the F2 data for stem length (tall:dwarf) and flower color (violet:white) is consistent with Mendel's law of independent assortment. 7.51 51. Can the deviation of observed values from expected values be attributed to random chance? Yes