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Biology Chapter 13

Meiosis and Sexual Life Cycles

TermDefinition
Asexual Reporduction Only one cell(parent cell) required, accomplished by cell division. Produces clones
Clones Genetically identical organisms
Sexual Reproduction Two cells(two parent cells) required. Will not be genetically identical. There are three way this genetic diversity(variety) will be accomplished within a population... 1. Random fertilization.. 2. Crossing over.. 3. Independent Assortment
Random Fertillzation Random fertilization of genetically different gametes
Crossing Over Crossing over of the non-sister chromosomes in prophase I
Independent Assortment Independent assortment in Metaphase I
The Sexual Life Cycle Alternates between cells that are 2n and 1n
Fertilization The union of gametes which produces a zygote(2n)
Meiosis Meiosis involves two successive divisions of a diploid (2N) eukaryotic cell of a sexually reproducing organism that result in four haploid (1n) cells, each with half of the genetic material of the original cell. Consists of meiosis I and meiosis II
Meiosis I Reduction Division because chromosome count is reduced(2n --> 1n). Consists of the phases... 1. Prophase I.. 2. Metaphase I.. 3. Anaphase I.. 4. Telophase I.. 5. Cytokinesis
Prophase I Chromosomes become visible, crossing-over occurs, the nucleolus disappears, the meiotic spindle forms, and the nuclear envelope disappears.
Synapsis The state by which paired homologous chromosomes become physically connected to each other along their length by a zipper-like protein structure forming the Synaptonemal Complex
Tetrad The bundle of four chromatids which could participate in crossing over
Chiasmata X-shaped regions where a crossing over has occured
Crossing Over A genetic rearrangement between non-sister chromatids involving the exchange of corresponding segments of DNA molecules. "Gene swapping"
Metaphase I The pairs of chromosomes (bivalents) become arranged on the metaphase plate and are attached to the now fully formed meiotic spindle. Spindle fibers from each pole of the cell attach to one chromosome of each pair facing that pole
Law or Principle of Independent Assortment Random alignnment of one pair of homologous chromosomes is independent of the random alignment of a second pair in Metaphase I
Anaphase I The homologous chormosomes separate from each other and move toward opposite poles(2n ---> 1n). Each chromosome still consists of two sister chromatids
Law or Principle of Segregation The separation of homologous chromosomes to opposite poles and eventually into separate cells
Telophase I The homologous chromosome pairs reach the poles of the cell, nuclear envelopes form around them, and cytokinesis follows to produce two cells. This cell began with 46 chromsomes, but each daughter cell now has 23 chromosomes
Cytokinesis The homologous chromosome pairs reach the poles of the cell, nuclear envelopes form around them, and cytokinesis follows to produce two cells.
Prophase II Meiosis II begins without any further replication of the chromosomes. In prophase II, the nuclear envelope breaks down and the spindle apparatus forms.
Metaphase II The chromosomes become arranged on the metaphase plate, much as the chromosomes do in mitosis, and are attached to the now fully formed spindle. For each chromosome, each kinetochore is attached to a kinetochore microtubule coming from that pole.
Anaphase II The centromeres(sister chromatids) separate, and the two chromatids of each chromosome move to opposite poles on the spindle. The separated chromatids are now called chromosomes in their own right.
Telophase II A nuclear envelope forms around each set of chromosomes and cytokinesis occurs, producing four daughter cells, each with a haploid set of chromosomes. Because of crossing-over, some chromosomes have recombined segments of the original parental chromosomes
Created by: TimBiology1
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