Ch.2 Practice questions: Multiple Choice Questions: In an organism with 52 chromosomes, how many bivalents would be expected to form during meiosis? 52 26 13 104 208 In a healthy male, how many sperm cells would be expected to be formed from a) 400 primary spermatocytes, b) 400 secondary spermatocytes? a-800, b-800 a-1600, b-1600 a-1600, b-800 a-400, b-400 a-100, b-800 In a healthy female, how many secondary oocytes and first polar bodies would be expected to form from 100 primary oocytes? 200,50 100,50 200,300 100,100 50,50 If the G1 somatic cell nucleus in a female insect contains 2 picograms of DNA, how much DNA would be expected in the metaphase I cycle of the same cell? 16 picograms 32 picograms 8 picograms 4 picograms None of the above What is the outcome of synapsis? side-by-side alignment of nonhomologous chromosomes dyad formation monad movement to opposite poles side-by-side alignment of homologous chromosomes chiasma segregation Which of the following occur in meiosis but NOT in mitosis? Separation of sister chromatids on microtubules Pairing of homologous chromosomes Recombination between sister chromatids I only II only I and II II and III If cells are blocked in meiotic metaphase II and prevented from moving on in meiosis, which one of the following will be prevented? Crossing over Separation of homologous chromosomes Separation of sister chromatids Breakdown of the nuclear envelop During interphase of the cell cycle DNA recombines Sister chromatids move to opposite poles The nuclear membrane disappears RNA replicates DNA content essentially doubles A gamete normally contains how many copies of each chromosome? 2 1 4 None of the above How many haploid sets of chromosomes are present in an individual cell that is tetraploid (4n)? 8 4 2 16 TRUE/ FALSE: A chromosome may contain one or two chromatids in different phases of the mitotic or meiotic cell cycle. T / F If a typical G1 nucleus is 2n and contains two complements (2C) of DNA, a prophase I cell is 2n and contains 4C DNA. T / F During meiosis chromosome number reduction takes place in anaphase II. T / F The centromere of a chromosome separates during anaphase. T / F The meiotic cell cycle involves two cell divisions and two DNA replications. T / F Short Questions and problems: Discuss the concepts of homologous chromosomes, haploidy and diploidy. What characteristics do two homologous chromosomes share? If two homologous chromosomes of chromosome # 12 fail to separate during meiosis I, how many copies of chromosome # 12 will the resulting gametes have? In what way does the second division of meiosis differ from mitosis? If children obtain half their genes from one parent and half from the other parent, why aren?t siblings identical? Human cells normally have 46 chromosomes. For each of the following stages, state the number of chromatids (or chromosomes) present in a human cell. Metaphase of mitosis Metaphase I of meiosis Telophase of mitosis Telophase I of meiosis Telophase II of meiosis In a diploid organism of 2n=10, assume that you can label all the centromeres derived from both female and male parent. When this organism produces gametes, how many male- and female- labeled centromere combinations are possible in the gametes? a) Contrast spermatogenesis and oogenesis. b) What is the significance of the formation of polar bodies? Regarding the mitotic cell cycle, what is meant by a check-point? What are the different checkpoints and how do they serve us? Trisomy 21 or Down syndrome occurs when there is a normal diploid chromosomal complement of 46 chromosomes plus one extra chromosome # 21 (total 47 chromosomes). Assume that a mating happens between a Down syndrome female and a normal male (46 chromosomes). What proportion of offspring will be expected to have Down syndrome? Explain. Assume that an organism has a diploid chromosome number of six. Two chromosomal pairs are telocentric, and the other pair is metacentric. Assume that sex chromosomes are morphologically identical. Draw diagrams to show the chromosomes as you would expect them to appear at the following stages: Primary oocyte (metaphase) Secondary spermatocyte (metaphase) First polar body (metaphase) In a diploid organism with a chromosome no of 46 (2n = 46), and G1 nuclear DNA content of 13 picograms; What is the haploid number? During metaphase of mitosis how many chromatids are present in each somatic cell? How many haploid sets of chromosomes are present in each cell? What is the nuclear DNA content of the G2 cell? A species of wheat has a chromosome number of 30, while a species of rye has a chromosome number of 14. Sterile hybrids can be produced by crossing these two plants. What would be the expected chromosome number in the somatic cells of the hybrids? The G1 nuclear DNA content of wheat is 5.5 picograms, and that of rye is 16.8 picograms. What would be the expected DNA content in a metaphase somatic cell of the hybrid?
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