1.6 Meiosis Flashcards
(22 cards)
How many daughter cells are produced in meiosis?
Four.
Meiosis is what division? What does this mean?
Reduction. This means that the chromosome number is reduced from diploid (2n) to haploid (n).
What is the product of meiosis?
Gametes (sex cells).
What does meiosis ensure?
That the chromosome number of individuals remains the same from generation to generation in sexually reproducing populations.
How is reduction division achieved?
By having two divisions of the chromosomes. The DNA content of cells is reduced by half in the first division and again in the second division.
How is each cell genetically different?
Because of crossing over and random assortment during meiosis.
What does random fusion of gametes mean?
The zygotes and offspring developing from them are all genetically different.
What are the stages in meiosis I?
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
- Cytokineses
What are the stages in meiosis II?
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
- Cytokinesis
What happens in prophase I?
Chromatin condenses and chromosomes become visible as two sister chromatids joined by a centromere. Homologous chromosomes pair up forming bivalents. Crossing over between the maternal and paternal chromosomes of the homologous pair takes place at chiasmata. In animal cells, the centrioles migrate to the poles. The spindle forms and the nuclear membrane disintegrates.
What happens in metaphase I?
The bivalents migrate to the equator of the cell and attach to the spindle by the centromeres. The orientation of the maternal and paternal homologs towards the poles is random, this is random assortment.
What happens in anaphase I?
The spindle contracts and pulls the chromosomes towards each pole. Each chromosome is still composed of two chromatids, although they are not genetically identical because of crossing over.
What happens in telophase I?
The chromosomes reach the poles and the nuclear membranes reform. Each nucleus is haploid as the chromosomes are not paired.
What happens in cytokineses in meiosis I?
Forms two cells each with a haploid nucleus.
What happens in prophase II?
The chromosomes condense and become visible as two chromatids joined by a centromere. The spindle forms and the nuclear membranes disintegrate.
What happens in metaphase II?
The chromosomes migrate to the equator and attach to the spindle by the centromere. The chromatids are not identical, each one in the chromosome can orientate towards a pole randomly – random assortment.
What happens in anaphase II?
The centromeres divide as the chromatids are pulled to the poles by contraction of the spindle. The chromatids are now called chromosomes.
What happens in telophase II?
The chromosomes reach the poles and the nuclear membranes reform.
What happens in cytokineses in meiosis II?
Each cell now divides, forming two daughter cells.
Where does meiosis take place?
In the reproductive organs of plants, animals and some protoctistans, prior to sexual reproduction.
What occurs in meiosis I (basic)?
Homologous pairs of chromosomes are separated.
What occurs in meiosis II (basic)?
Pairs of chromatids are separated.
