15
.
Describe what happens to the tetrads after they form.
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Prophase I of meiosis forms the tetrads. They line up at the midway point between the two poles of the cell to form the metaphase plate. There is equal chance of a microtubule fiber to encounter a maternally or a paternally inherited chromosome. Orientation of each tetrad is independent of the orientation of other tetrads.
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Prophase II of meiosis forms the tetrads. They line up at the midway point between the two poles of the cell to form the metaphase plate. There is equal chance of microtubule fiber to encounter maternally or paternally inherited chromosome. Orientation of each tetrad is independent of the orientation of other tetrads.
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Prophase I of mitosis forms the tetrads. They line up at the midway between the two poles of the cell to form the metaphase plate. There is a low chance of a microtubule fiber to encounter both a maternally and a paternally inherited chromosome. Orientation of each tetrad is independent of the orientation of other tetrads.
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Prophase I of meiosis forms the tetrads. They line up at the midway between the two poles of the cell to form the metaphase plate. There is a chance of microtubule fiber to encounter maternally inherited chromosome. Orientation of each tetrad is independent of the orientation of other tetrads.
16
.
Which of the following distinguishes metaphase I from metaphase II?
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Metaphase I occurs when homologous chromosome pairs align on the metaphase plate. Metaphase II has sister chromatids of chromosomes aligned at the metaphase plate.
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Metaphase I occurs when chromosomes appear in homologous pairs at the metaphase plate. Metaphase II has single sister chromatids of chromosomes on the spindle.
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Metaphase I occurs when chromosomes separate the homologous pairs on the spindle. Metaphase II has a single line of chromosomes on the plate.
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Metaphase I occurs when chromosomes appear in homologous pairs on the spindle. During metaphase II, the chromosomes line up in a double line across the spindle.
17
.
Though the stages of meiosis have the same names as the stages of mitosis, they exhibit fundamental differences. Compare and contrast the two processes to accurately state their main differences.
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Meiosis differs from mitosis in that the number of chromosomes is halved and genetic variation is reduced in meiosis, but not in mitosis.
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Meiosis differs from mitosis in that the number of chromosomes is halved and genetic variation is introduced in meiosis, but not in mitosis.
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The metaphase and telophase portions of meiosis and mitosis are the same, but anaphase and prophase portions are different. Meiosis and mitosis differ overall in the number of chromosomes involved.
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The prophase and telophase portions of meiosis and mitosis are the same, but anaphase I and anaphase are different. Meiosis II and mitosis are also the same and have the same number of chromosomes.
18
.
Explain how the orientation of homologous chromosomes during metaphase I of meiosis contributes to greater variation in gametes.
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The random alignment of homologous chromosomes at the metaphase plate ensures the random destination of the chromosomes in the daughter cells.
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Because homologous chromosomes dissociate from the spindle fibers during metaphase I, they move randomly to the daughter cells.
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The homologous chromosomes are paired tightly during metaphase I and undergo crossover as the synaptonemal complex forms a lattice around them.
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Recombination of maternal and paternal chromosomes occurs in metaphase I because the homologous chromosomes are not connected at their centromeres.
19
.
The Red Queen hypothesis, a reference to Lewis Carroll's book, Through the Looking Glass, seeks to explain particular aspects of evolution. Explain how the Red Queen’s catchphrase, “It takes all the running you can do to stay in the same place,” describes co-evolution between competing species.
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When a sexually reproducing species and an asexually reproducing species compete for the same resources, they both “run [evolve] in the same place” because the increased genetic variation in the sexually reproducing species balances the loss in energy that species uses to find and attract mates.
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When one species gains an advantage with a favorable variation, selection pressure increases on another species with which it competes. This species must also develop an advantage or it will be outcompeted. The two species “run [evolve] to stay in the same place.”
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When one species develops a mutation that decreases its ability to survive, a competing species will become better able to survive even though it has not changed in any way. In effect, this second species “runs [evolves] to stay in the same place.”
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When two asexually reproducing species encounter rapid environmental change, the species that is also able to reproduce sexually will outcompete the other. This way it can “run [evolve] to stay in the same place.”
20
.
Which three processes lead to variation among offspring that have the same two parents?
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genetic recombination, fertilization, meiosis
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crossing over, random chromosome assortment, genetic recombination
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meiosis, crossing over, genetic recombination
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fertilization, crossing over, random chromosome assortment
21
.
Compare the three main types of life cycles in multicellular organisms as described below. Determine which comparison is accurate and which also gives an appropriate example of an organism that employs each type.
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In a diploid-dominant life cycle, the diploid multicellular stage is present, as in humans. Haploid-dominant life cycles have a multicellular haploid stage, as in fungi. In alternation of generations, both haploid-dominant and diploid-dominant stages are multicellular and the stages alternate, as in plants.
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In a diploid-dominant life cycle, the unicellular stage is present, as in humans. Haploid-dominant life cycles have a multicellular haploid stage, as in fungi. In alternation of generations, both haploid-dominant and diploid-dominant stages are multicellular and the stages alternate, as in plants.
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In a diploid-dominant life cycle, a haploid multicellular stage is present, as in humans. Haploid-dominant life cycles have a multicellular haploid stage, as in fungi. In alternation of generations, both haploid-dominant and diploid-dominant stages are multicellular and the stages alternate, as in plants.
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In a diploid-dominant life cycle, a multicellular diploid stage is present, as in algae. In a haploid-dominant life cycle, a multicellular haploid stage is present, as in plants. In alternation of generations, both haploid-dominant and diploid-dominant stages are multicellular and the stages alternate, as in humans.