Cell reproduction and the Continuity of Life: Meiosis Flashcards
Test review
What is meiosis (reductive division)?
Type of cell division that produces gametes/sex cells (sperm/eggs). Occurs in special sex organs. Chromosomes replicate once, but divide twice, producing four haploid gametes from a single diploid cell.
What is the function of meiosis?
Meiosis ensures that the number of chromosomes in a species remains constant from generation to generation. Humans have 46 chromosomes, so by producing 23 chromosome sperm and eggs, the two combine to have 46 chromosomes. If diploid cells fertilized diploid cells, chromosome count would double generationally.
What happens in prophase 1?
Same as mitosis prophase, however homologous chromosomes pair up and form tetrads. Homologous chromosomes in tetrads exchange genetic material, increasing variation (crossing over). Mitotic spindle forms.
What happens in metaphase 1?
Mitotic spindle lines tetrads up along cell equator, one homologous chromosome on each side
What happens in anaphase 1?
Mitotic spindle pulls apart homologous chromosomes (disjunction), making each cell end have a haploid cluster of chromosomes (each with identical sister chromatids).
What happens in telophase 1?
Cell divides into 2 smaller haploid cells (by cytokinesis) and the nuclear membrane reforms around each chromosome group.
What happens in interphase 1?
Exactly the same things as mitosis.
What happens in interphase 2?
Chromosomes may reform into chromatin for a short time after telophase 1.
What happens in prophase 2?
Chromatin condenses in both cells, forming sister chromatids which then move towards the cell equator.
What happens in metaphase 2?
The sister chromatids line up along the cell equators, one on each side.
What happens in anaphase 2?
Mitotic spindle pulls sister chromatids apart, one to each side of the cells. Each chromatid is now just a chromosome.
What happens in telophase 2?
Both cells experience cytokinesis, creating 4 haploid daughter cells in total. Nuclear membrane reforms around each set of chromosomes.
What is independent assortment of chromosomes?
The result of homologous chromosomes lining up randomly in metaphase 1. Each chromosome can be on either side in relation to an adjacent pair, resulting in various combinations of genetic material as they are pulled apart in anaphase 1 and increasing variation.
