The important cells of our body


  1. In Interphase I, I would look to see if the centrosomes were still floating about on their own, and had no mitotic spindle formation. I would also make sure look to make sure the nucleolus is still condensed inside a nuclear membrane.
  2. In Prophase I, I would check to see a mitotic spindle formation, and distinct chromosome pairs forming in the a partly- dissolved nuclear membrane. I would look for cross-over points as well, where DNA has been exchanged within the tetrads formed.

    In Metaphase I, I would look for alignment parallel with the equatorial plate. I would look for the random assortment, and I would make sure that the chromosomes were still somewhat linear, to assure we are not yet in Anaphase.

    In Anaphase I, I would look to see the chromosomes getting pulled by the centromeres to opposite sides of the cell, not yet creating a fold where the two cells will later divide.

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    In Telophase I, cytokinesis occurs and the cytoplasm divides. Nuclear membranes in both cells develop, and the chromosomes de-condense in both cells.

    In Prophase II I would look for condensed chromosomes in both cells, and mitotic spindles again forming. There must be two chromosomes in each cell.

    In Metaphase II, the chromosomes of both cells line up parallel to the equatorial plate, microtubules will attach to the centromeres.

    In Anaphase II, the centromeres divide and each chromatid becomes an independent chromosome that is pulled to opposite sides of the cell.

    During Telophase II, I would look for similar de-condensing in the nuclei of the 4 cells, with nuclear membrane development.

  3. Homologous chromosomes do not travel to the same daughter cell. Whole chromosomes are not transferred to the daughter cells during the second division. Sister chromatids do not travel to the same daughter cell. Homologous chromosomes include two chromosomes that have the same loci for the same trait, but the alleles for the traits can be different. Sister chromatids, however, are absolutely identical copies (until crossover), including the exact same alleles for each trait in their specific loci. This does mean that they are homologous as well, which constitutes the similarity.
  4. There are 8,388,608 possible combinations of chromosomes for humans. This video demonstrates the law of segregation, how pairs of homologous chromosomes separate randomly to two poles during meiosis, and that their separation is random.
  5. Random orientation of the homologous chromosomes occurs in metaphase I of meiosis.

    A cell with 4 pairs of chromosomes could produces 16 different combinations during meiosis.

    In a cell with 3 pairs of chromosomes, there are 2 gametes out of the possible 8 that will contain only the maternal chromosomes.

    The region of the cell where chromosome pairs allign is called the plate.

    Homologous chromosomes do not bind to the spindle axis.

  6. Both mitosis and meiosis involve the division of cells. Prior to both, DNA replicates, and condense into chromosomes. Meiosis occurs only in autosomes, and mitosis is specifically the division of somatic cells. Meiosis includes crossovers in which DNA is shared between them, but mitosis does not include this process. Also, meiosis ends with half the number of chromosomes in each gamete than they started with, whereas the number of chromosomes in mitosis doesn't change.
  7. The number of cells produced during meiosis is twice the number produced in mitosis.

    The number of chromosomes in daughter cells produced by meiosis is half the number of chromosomes in cells produced by mitosis.

    Crossing-over is a feature unique to meiosis; it does not occur during mitosis.

    Daughter cells produced during meiosis are not identical.

    Chromosomes do replicate prior to mitosis and meiosis.

  8. The three unique features of meiosis include synapsis, homologous recombination, and reduction division. Synapsis is when the chromosomes that are copied before meiosis create structures where crossing- over can occur. These paired chromosomes can then exchange DNA when they are temporarily joined like this, and homologous recombination is another name for it. Reduction division is the result of the entire process. Half of the original number of chromosomes can be found in each of the four gametes, which makes sense because each parent provides half the chromosomes for the zygote.
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    Synapsis, homologous recombination, and reduction division are all unique to meiosis.

    A crossover during meiotic division is an exchange of genetic information between non- sister chromatids of homologous chromosomes.

    The four daughter cells found at the end of meiosis have one of each pair of chromosomes found in the parent cell.

    Crossing over only occurs during meiosis I.

    Chromosome duplication in meiosis I and meiosis II.

  10. A cross between two heterozygotes should result in ¾ of them displaying the dominant trait.
  11. A phenotypic ratio of 3:1 will result from a monohybrid cross between two heterozygotes for that trait when segregation occurs during meiosis.

    When a parent homozygous for a dominant trait is crossed with a parent homozygous for the recessive, all of the offspring in the F1 generation will display the dominant trait. However, when allowed to self fertilize (if possible, or when mated with another heterozygote for that trait), the resulting F2 generation will include 3 offspring that display the dominant trait, and only one that displays the recessive one.

    A genetic cross between two F1-hybrid pea plants for spherical seeds will yield 75% spherical seeds, when spherical seeds are dominant.

    A genetic cross between two F1-hybrid pea plants having yellow seeds will yield 25% with green seeds, when green is dominant.

  12. In a dihybrid cross, (d is dominant, r is recessive), 25% of the gametes will be dd, 25% dr, 25% rd, and 25% rr.
  13. Independent assortment results in a phenotypic ratio of 9:3:3:1 in a cross between two heterozygous parents for both traits.

    Heterozygous dihybrid crosses result in 9:3:3:1 phenotypic ratios.

    A heterozygous individual for traits S and Y (these being dominant alleles), would be able to produce the gametes SY, Sy, sY, and sy.

    You would not expect to find among the gamete SsYY in the offspring of a SsYy x ssyy test cross.

  14. In a cross between a white-eyed female fruit fly and red-eyed male, 0% of the female offspring will have white eyes.
  15. In a cross between a purebred recessive male and a purebred dominant female, none of the offspring can express the recessive trait.

    A white-eyed female fruit fly is crossed with a red-eyed male will produce females with red eyes, and males with white eyes.