Meiosis Flashcards
What is the purpose of Meiosis?
Meiosis is the process of producing haploid gametes by reducing the number of chromosomes by half.
How many cell divisions occur and how many daughter cells are produced during
meiosis?
Two cell divisions; four daughter cells are produced.
Why is meiosis important in organisms that reproduce sexually?
Meiosis is important because it reduces the chromosome number by half in cells that fuse during sexual reproduction thus ensuring that the resulting organism has the correct number of chromosomes. Meiosis provides for genetic diversity through the crossing over.
What is a germline cell?
Germline cells are cells that produce gametes.
What are the stages of Meiosis?
Prophase I, Metaphase I, Anaphase I Telophase I, Cytokenisis - End Meiosis I.
Prophase I, Metaphase II, Anaphase II, Telophase II, Cytokenisis - End Meiosis II
What happens in Prophase I:
Prophase I: Starts with a diploid cell. The chromatin condenses into chromosomes and the nuclear membrane breaks down. The centrosomes are duplicated and move to opposite ends of the cell. The sister chromatids pair to their corresponding homologous chromosomes forming a tetrad (4 chromatids). Crossing over occurs. The meiotic spindle forms.
What happens in Metaphase I:
Metaphase I: Pairs of homologous chromosomes move to the central axis of the spindle apparatus. Tubes come from the centrioles attaching to the centromere.
What happens in Anaphase I:
Anaphase I: The spindle fibres separate the homologous chromosomes in each tetrad, moving them to opposite sides of the cell.
What happens in Telophase I + Cytokinesis:
Telophase I + Cytokenisis: Two nuclei form with the nuclear membrane reforming around the groups of chromosomes. The sister chromatids are no longer identical because of the crossing over of alleles. The spindle breaks down. The cytoplasm divides forming two genetically different haploid cells.
What happens in Prophase II:
DNA does not replicate before this phase. The nuclear membrane breaks down, and the centrosomes duplicate lining up at opposite ends of the cell. A new spindle forms.
What happens in Metaphase II:
Chromosomes line up at the equator of the cell, and tubes from the centrioles attach to the centromeres.
What happens in Anaphase II:
Centromeres divide and the sister Chromatids move to opposite ends of the cell. They are now called chromosomes.
What happens in Telophase II + Cytokinesis:
A nuclear membrane reforms around the groups of chromosomes, and the spindle breaks down. The cytoplasm of the parental cell divides resulting in 4 genetically different haploid daughter cells.
What is crossing over?
The swapping of genetic material occurring and sister chromatids from each parent align so that similar DNA sequences cross over one another. This makes genetic diversity.
What are gametes?
Gametes are sex cells, They are haploid cells that result from Meiosis.
