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Unit 7: Cell Division

Last updated

May 14, 2022
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- 6.7: Ribosomal RNA (rRNA) Gene Cluster
- 7.1: Chromosomes

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7.2: The Cell Cycle
This page discusses eukaryotic cell division, detailing the phases of the cell cycle: G1, S, G2, and M. It explains the process of genome doubling and halving, emphasizing the role of proteins like the anaphase-promoting complex (APC) in controlling division. Checkpoints monitor DNA integrity and can pause the cycle if damage is detected, with mutations in these genes associated with cancer.
7.3: Mitosis
This page addresses the complexities of DNA separation during cell division, highlighting an illustration of a single human chromosome's DNA. It notes that only a small portion of the chromosome is depicted, emphasizing the overall challenge with all 46 chromosomes. The solution involves duplicating chromosomes in the S phase to create dyads, condensing them for easier separation through ATP and condensin proteins, and ensuring even distribution of sister chromatids to daughter cells.
7.4: Polyploidy
This page discusses polyploidy, the condition of having more than two sets of chromosomes, mainly observed in plants like wheat and sugar cane. It can occur naturally through errors in gamete formation or be induced artificially. Polyploidy can lead to speciation, with hybrids often sterile while polyploid plants remain fertile. Although rare in animals, some instances, such as a tetraploid rat, have been recorded.
7.5: Endoreplication
This page discusses endoreplication, a process of DNA replication during the S phase without mitosis or cytokinesis, found in some animal and plant cells. Variants include replication with mitosis but no cytokinesis and multiple rounds of replication without new nuclei. This can cause polyploidy or polyteny, the latter evident in Drosophila larva, where polytene chromosomes allow for gene amplification and increased expression.
7.6: Sex Chromosomes
This page explores human sexual chromosomes, focusing on the roles of X and Y chromosomes in sex determination, the significance of the SRY gene, and examples of genetic conditions like hemophilia and Turner syndrome. It also discusses sex determination in other species, including Klinefelter's syndrome, the role of the X chromosome in fruit flies, and ZZ/ZW systems in birds.
7.7: Meiosis
This page covers meiosis, a crucial process in sexual reproduction that produces four haploid cells from one diploid cell, involving two divisions and featuring genetic recombination and chromosome assortment for diversity. It highlights the importance of checkpoints to prevent errors, which, if present, can lead to chromosomal abnormalities such as monosomy, often lethal, and trisomy, which can result in conditions like Down syndrome.

Thumbnail: Life cycle of the cell. (CC BY-SA 4.0; BruceBlaus).

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