What are the different shapes/forms dna can be in?
2 answers:
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Complete question:
In the attached files you will find the sentences used to complete this problem, and their corresponding boxes.
Answer:
Mitosis:
- Homologous chromosomes do not pair
- One row of chromosomes line up in the center of the cell
- The cell nucleus divide only once
- Two diploid daughter cells form that are identical to their parental cells
Meiosis:
- Each replicated chromosome pair with its corresponding homologous pair
- Tetrads form, and crossing-over sometimes occur
- Paired homologous chromosomes line up across the center of the cell
- Four haploid daughter cells form that are not identical to their parental cells
Explanation:
There are two principal types of cells in the organism: Somatic diploid cells (2n) that reproduce by the process of mitosis, and germ cells that are diploid reproductive cells in charge of gamete production. These germ cells suffer both mitosis (to form more sexual cells) and meiosis (giving place to haploid gametes, called sperm and egg cells, through the gametogenesis process). Both somatic cells and germinal cells will end their cycle becoming two daughter cells with the same genetic dotation.
Gametes´destiny is to merge in the process of fecundation, during which a new diploid cell called zygote emerges through fertilization. The zygote is a complete cell from the structural point of view that suffer successive mitosis to form the new organism.
- <u>Meiosis</u> is a process by which, from a diploid germ cell (2n), four daughter cells with a haploid chromosome number (n) are produced. Each daughter cell has half of the chromosomes of the original one. There are two phases in meiosis: the first one in which occurs a chromosome´s reduction division, and the second one where the cell suffers a new division, but this one is not a reductive one.
- In the first phase, Meiosis I: Chromosomes condensate and became visible. Occurs crossing-over between homologous chromosomes in the equatorial plane. Crossin-over makes the daughter cells to be genetically different from the original one. After crossing-over, homologous chromosomes get separated again. Then occurs cytokinesis and chromosomes became lax again.
- In the second phase, Meiosis II: Chromosomes condensate again, they join the spindle apparatus and migrate to the equatorial plane. Centromeres divide and each chromatid goes forward to each pole. Once in the poles the chromosomes became lax again and occur cytokinesis.
- Mitosis is a process by which, from a diploid somatic cell (2n), two daughter diploid cells (2n) are produced. During mitosis, the cell duplicates and then separates. Mitosis occurs in only one phase. In the prophase, it occurs chromosomes condensation and nuclear membrane breaks. During the metaphase, fibers of the spindle apparatus capture chromosomes and take them toward the center of the cell, to the equatorial plane, where they line up. Each chromatid joins with a microtubule of opposites poles. Sister chromatids are held together until they reach the Anaphase, during which other enzymes are activated to break the bonds and separate the chromatids, which migrate to the opposite poles. In telophase, the duplicated chromosomes are already in the corresponding poles, and the nuclear membrane forms again in each pole. Finally, occurs cytokinesis.
