Chapter 12 Meiosis and Sexual Reproduction

Homologous Chromosomes

  • Homologous chromosomes describes 2 chromosomes that in a pair. It only refers to chromosomes, not a cell.
  • Homologous chromosomes are often found in a pair with one chromosomes from the mother and the other from the father. They are paired so that they have the same characteristics as their partner, for example chromosome 16 of the father would be paired with chromosome 16 of the mother.

Alleles

  • Alleles are different forms of the same gene. They are responsible in creating new combonations of traits in organisms.
  • They can cause rises in mutation, and are the basis of differences in shared traits.
  • They can be found in homologous chromosomes, where the genes of the pairs are the same but alleles can differ them slightly.
  • An example would be eye color be a gene, but the different possibilities of eye color are the alleles.

Gene

  • Genes are sections of DNA that code specific things.
  • They can have differences because of alleles.

Haploid

  • Haploid describes a cell that has half of a diploid cell. They are writtten (n).
  • In humans, haploid cells have 23 chromosomes. Because they are not diploid, there are no homologous chromosomes.
  • Haploid cells are often sex cells, or gametes.

Meiosis

Prophase 1

The centrioles move the either end of the cell and send out their spindle apparatus, attaching to each chromosomes, not chromatid. The homologous chromosomes condense, and the nuclear envelope breaks down.

Metaphase 1

The homologous chromosomes pairs are aligned midway between spindle poles.

Anaphase 1

The homologous chromosomes separate and begin heading toward the opposite spindle poles. Cytokinesis begins at the end of the stage

Telophase 1

The two clusters of chromosomes reach opposite ends of the cell, at the spindle poles. Two new nuclear envelopes form around the clusters, creating 2 new, haploid cells

Prophase II

The chromosomes condense, the nuclear envelope breaks down, and spindle microtubules are sent out and attach to each sister chromatids. Meiosis 2 is more like mitosis.

Metaphase II

The duplicated chromosomes align in the middle of each cell.

Anaphase II

The sister chromatids seperate and head to either end of the cell. Now the chromosomes are not duplicated.

Telophase II

The sister chromatid cluster at the spindle poles. A new nuclear envelope forms around the clusters, forming 4 new haploid cells.

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