5.1-2 Meiosis only Flashcards
What is meiosis?
- a process that creates haploid gamete cells in sexually reproducing diploid organisms
What does meiosis result in, in terms of daughter cells?
- results in daughter cells with half the number of chromosomes as the parent cell
We know that meiosis results in daughter cells with half the number of xmes as the parent cell. Use this information with humans as an example.
- humans are diploid: 2n=46
- meiosis produces sperm and eggs that are haploid: n=23
- involves two rounds of cell division (meiosis I and meiosis II)
Meiosis is similar to mitosis, but there are some key differences. What occurs in mitosis?
- occurs in somatic cells
- 1 division
- results in 2 diploid daughter cells
- Daughter cells are genetically identical
Meiosis is similar to mitosis, but there are some key differences. What occurs in meiosis?
- forms gametes (sperm/egg)
- 2 divisions
- results in 4 haploid daughter cells
- each daughter cell is genetically unique
What are three key events in meiosis that are unique?
- Prophase I (synapsis and crossing over)
- metaphase I (tetrads (homologous pairs) line up at the metaphase plate)
- anaphase I (homologous pairs separate)
What occurs in interphase?
Cell goes through G1, S (DNA is copied), and G2
What occurs in Prophase I? (3)
Synapsis: homologous chromosomes pair up and physically connect to each other forming a tetrad
- crossing over (recombination) occurs at the chlasmata and DNA is exchanged between homologous pairs
- every chromatid that is produced has a unique combination of DNA
What is the chlasmata?
- region where non-sister xmes are connected
What occurs in metaphase I? (2)
- independent orientation: tetrads line up at the metaphase plate
—the recombinant chromosomes randomly assort themselves at the equator
What occurs in Anaphase I? (2)
- pair of homologous chromosomes separate
- sister chromatids are still attached
What occurs in Telophase I and cytokinesis? (3)
- nuclei and cytoplasm divide
- there is now a haploid set of xmes in each daughter cell
- each cell has one member of each homologous pair
What occurs in interkinesis?
Period of time between meiosis I and meiosis II
What occurs in Prophase II? (2)
- no crossing over (bc odd #]
- spindle forms
What occurs in metaphase II? (2)
- chromosomes line up at the metaphase plate
- because of crossing over in meiosis I, the chromatids are unique
What occurs in anaphase II?
- sister chromatids separate and move towards opposite poles
What occurs in telophase II and cytokinesis? (3)
- 4 haploid cells
- nuclei reappear
- each daughter cell is genetically unique
What are three ways that Meiosis leads to genetic variation?
- Crossing over
- Independent assortment of chromosomes
- Random fertilization
How does crossing over lead to genetic variation? Which stage does crossing over occur? (4)
- (recombination) occurs and DNA is exchanged between the homologous pairs
— every chromatid produced therefore had a unique combination of DNA - produces recombinant xmes which therefore exchange genetic material
- occurs at prophase I
How does independent assortment of chromosomes lead to genetic variation?
- chromosomes are randomly oriented along the metaphase plate during metaphase I
- each can orient with either the maternal or paternal chromosomes closer to a given pole
How does random fertilization lead to genetic variation?
- any sperm can fertilize any egg
Meiosis followed by fertilization ensures ___ _____ in sexually reproducing organisms, and provides genetic variation that plays a role in _____ ______.
Genetic diversity, natural selection
Meiosis is driven by the interaction of ______ components and uses ____ _____ that is required for the _____ and ______ of living systems.
- Sub cellular (organelles)
- Free energy (energy available to do work)
- Growth
- Reproduction
