The chromatin condenses to chromosomes


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  1. Meiosis:
  2. a. Interphase: chromatin are not condensed or visible under a light microscope, but are depicted in a condensed manner and centrosomes are together at the one pole

    b. Prophase I: chromatin condenses to chromosomes, mitotic spindle begins to form at centrosomes move to poles

    c. Metaphase I: crossed over chromosomes are aligned at the “metaphase plate” and connected to the mitotic spindle

    d. Anaphase I: each pair of chromosomes with 2 sister chromatids is pulled to the poles, where the shortened spindle fibers are connected to the centrosomes

    e. Telophase I: chromosomes condense to two separate chromatin, and nuclear envelopes form

    f. Prophase II: the chromatin recondenses to pairs of chromatids, and centrosomes begin to go to poles, creating spindle fibers

    g. Metaphase II: chromosomes are aligned, and connected to the mitotic spindle which is present in both halves of the cell

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    h. Anaphase II: centromeres divide, and the chromatids become separate chromosomes; also, they move to the opposite poles to the centrosomes

    i. Telophase II: nuclear envelope forms in all four separate cells, with an equal number of chromosomes in each envelope

  3. Answers:
  4. a. Hints:

    i. sister chromatids do not go to the same daughter cell

    ii. Homologous chromosomes do not travel to the same daughter cell

    b. Similarities:

    i. Same loci

    ii. Both homologous

    iii. Sister chromatids are homologous chromosomes

    c. Differences:

    i. Homologous have the same loci, but they can be different

    ii. Sister chromatids are EXACTLY alike, NO DIFFERENCE AT ALL

  5. Answers:
  6. a. There are 8388608 different combinations in humans

    b. This demonstrates the law of independent assortment because it shows how there are many different ways

    c. Statement 1: Random orientation of homologous chromosomes occurs in metaphase I of meiosis

    d. Statement 2: There are 16 possible chromosome orientations in a cell that has four pairs of chromosomes.

    e. Statement 3: For a cell that has three pairs of chromosomes, the fraction of gametes produced from this cell that will only contain only maternal chromosomes is 1/8.

    f. Statement 4: The region of the cell where chromosome pairs lineup is referred to as the plate.

    g. Statement 5: The actual structure that homologues bind to is called the spindle axis.

  7. Answers:
  8. a. 3 similarities between mitosis and meiosis:

    i. Chromosomes replicate from the parent cell

    ii. The nuclear membrane breaks down as the DNA organizes into chromosomes

    iii. Chromosomes separate to the poles where the centrosomes are once they are on the metaphase plate

    b. Statement 1: In meiosis, the number of cells produced is twice the number of cells produced by mitosis

    c. Statement 2: In meiosis, the number of chromosomes in daughter cells is half of those which are made in mitosis

    d. Statement 3: A unique feature of meiosis that is not shared by mitosis is its “crossing-over” before separating into daughter cells

    e. Statement 4: The daughter cells that are produced by meiosis are not identical, due to the law of independent assortment.

    f. Statement 5: A characteristic that is shared by mitosis and meiosis is the fact that, before they both begin, the chromosomes duplicate.

  9. Answers:
  10. a. Three unique features of meiosis:

    i. Synapsis: homologous chromosomes pair all along their length

    ii. homologous recombination: the exchange between two joined homologous chromosomes; crossing over

    iii. Reduction division: after meiosis is over, each cell only ends with half of its original number of chromosomes

    b. Statement 1: There are three unique features of meiosis: synapsis, homologous recombination, and reduction division

    c. Statement 2: Crossovers in meiosis occur when genetic material is exchanged between non-sister chromatids of homologous chromosomes

    d. Statement 3: In each of the four daughter cells that our produced in meiosis contain one of each pair of chromosomes of the parent cell

    e. Statement 4: The crossing over of chromosomes in meiosis occurs in prophase I

    f. Statement 5: The chromosome duplication in meiosis occurs before meiosis even

    begins, in the parent cell, in other words, leading into prophase I
  11. Answer:
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    a. Statement 1: In a heterozygous cross for Mendelian genetics, 3 out of 4 of the offspring should show the dominant trait through their phenotype, with 1 out of 4 showing the recessive.

    b. Statement 2: Mendel's law of segregation states that, when gametes are forming, the alleles for a single trait segregate from one another.

    c. Statement 3: One homozygous dominant and a homozygous recessive combine, all of their offspring will be heterozygous and reflect the dominant trait. If two heterozygous cross, or if the offspring self fertilizes, then the ¾ of the offspring will be heterozygous, and the other ¼ will show the recessive trait

    d. Statement 4: When two hybrid, aka heterozygous, parents are crossed; only 25% of the offspring will show the recessive trait, with 75% showing the dominant.

    e. Statement 5: When two hybrids cross, 25% of the offspring will show the recessive phenotype.

  13. Answers:
  14. a. Statement 1: In a dihybrid cross that has two heterozygous traits for each parent (XxYy), the distributions of the two alleles in the gametes are 25% XY, 25% Xy, 25% xY, and 25% xy.

    b. Statement 2: In a dihybrid cross, the phenotypic ratio of two heterozygous organisms' offspring is 9:3:3:1, if the gene pair assort independently during meiosis.

    c. Statement 3: Mendel invented the dihybrid cross so that one could tell the independent assortment of alleles during the formation of gametes.

    d. Statement 4: In a dihybrid cross, each gamete receives (in the terms of X and Y) both a dominant or recessive X, and a dominant or recessive Y.

  15. e. Statement 5: If a double heterozygous and a double recessive dihybrid cross is made, there will be no gametes that are homozygous dominant for either trait.
  16. Answers:
  17. a. Statement 1: When two sex linked genes are combined, one dominant and one recessive, then 0% will express the recessive trait.

    b. Statement 2: In sex-linked genetics, in order to pass down the recessive trait to offspring if paired with a dominant homologous male, the female must be heterozygous.

    c. Statement 3: In sex-linked genetics, when there is a cross between a homozygous dominant female and a homozygous recessive male, the percent of male traits that are present in the phenotype of the offspring is 0%

    d. Statement 4: In sex-linked genetics, just because the trait is from the female does not mean that it is always dominant or recessive. It can be dominant for one allele and recessive for another

    e. Statement 5: When two traits are crossed, with one being homozygous dominant and the other being homozygous recessive, the offspring will be heterozygous.