Meiosis - Cell Division Flashcards
(16 cards)
what are gametes
sperm and eggs
what are germlines
testis and ovarian
what is meiosis
one round of DNA replication that is followed by 2 rounds of of cell division in sexually reproducing organisms
end product is 4 haploid cells that are genetically different
explain the first phase of meiosis I
Prophase I
- nuclear envelope breaks down, chromosomes condense and spindle fibers forms
- crossing over between non sister chromatids occurs at chiasmata
- each chromatid is now a mix of DNA from each homologous chromosomes
explain the second phase of meiosis I
Metaphase I
- chromosomes are attached to the kinetochore microtubules at each centromere
- each pair is lined up independently
- paired homologous chromosomes have moved to the metaphase plate
- chiasmata line up on metaphase plate
explain the third phase of meiosis I
Anaphase I
- recombined homologous chromosomes disjoin
- sister chromatids stay attached to each other
- cell starts to elongate (non kinetochore microtubules exchange) and each duplicated chromosome moves to the poles at opposite ends of the cell
explain the fourth phase of meiosis I
Telophase I
- duplicated chromosomes (the pairs of sister chromatids) reach the poles at opposite ends of the cell
- spindle disappears and nuclear envelope reforms
Cytokinesis
in animal cells: cleavage furrow pinches into 2 cells
in plant cells: a cell plate forms
- cytoplasm divides, resulting in 2 haploid cells
- cells (and sister chromatids) are genetically different due to crossing over
explain the first phase of meiosis II
Prophase II
- spindle forms as the centromeres duplicate and move to opposite poles
- kinetochore microtubules attach to each duplicated chromosomes at the centromere (via the kinetochore proteins)
- each duplicated chromosomes is still composed of 2 chromatids attached at centromeres
explain the second phase of meiosis II
Metaphase II
- duplicated chromosomes align at the metaphase plate
- centromeres lie on the metaphase plate
explain the third phase of meiosis II
Anaphase II
- sister chromatids disjoin at the centromeres
- each chromatids becomes an independent daughter chromosome
- daughter chromosomes move towards opposite as their kinetochore microtubules shorten
- the non kinetochore microtubules lengthen and the cell elongates
explain the fourth phase of meiosis II
Telophase II & Cytokinesis
- 2 daughter nuclei with nuclear envelope form in the cell
- the meiotic division of one parent cell produces 4 daughter cells
- each daughter cell has a haploid set of (unreplicated) chromosomes
- the 4 daughter cells are genetically distinct from one another and from the parent cell
what is a chiasmata
the visible points of connection between homologous chromosomes during meiosis, specifically during the prophase I stage, where they are the physical manifestation of crossing over, or the exchange of genetic material between non-sister chromatids
what is the end product of meiosis I
Two haploid cells are the end result of the first meiotic division. The cells are haploid because at each pole, there is just one of each pair of the homologous chromosomes. Therefore, only one full set of the chromosomes is present.
what is the end product of meiosis II
The end product of meiosis II is four haploid daughter cells. These cells are formed from the two haploid cells that result from meiosis I. During meiosis II, sister chromatids separate, ensuring each daughter cell receives a single set of chromosomes. This process ultimately produces the gametes (sperm or egg cells) with half the number of chromosomes as the original cell.
what is crossing over in cell division
the exchange of genetic material between homologous chromosomes during meiosis
what are the 2 reasons for sexual reproduction
- sexual production produces genetic diversity through
- independent assortment of chromosomes
- crossing over
- random fertilization of gametes - genetic diversity allows selective responses
- spatially variable environments
- changing environments
- sib-sib competition
