Meiosis Flashcards
(14 cards)
What happens in meiosis 1?
Reduction division when pairs of homologous chromosomes are separated into two cells - cells are haploid.
What happens in meiosis 2?
Pairs of chromatids present in each daughter cell are separated, forming two more cells - 4 haploid daughter cells.
What happens in prophase 1?
Chromosomes condense, nucleolus disappears, nuclear envelope disintegrates. Spindle formation begins.
Homologous chromosomes pair up to form bivalents - chromatids entangle while being brought together (crossing over).
What happens in metaphase 1?
Same as mitotic metaphase - instead of individual chromosomes, homologous pairs line up along metaphase plate.
- orientation of each pair is random and independent - independent assortment which leads to genetic variation.
What happens in anaphase 1?
Homologous chromosomes pulled to opposite poles - chromatids stay joined together.
- Sections of entangled DNA of sister chromatids break off and rejoin which can result in exchange of DNA. The point at which this happens = chiasmata.
This allows for the formation of recombinant chromatids with new allele combinations (genetic variation).
What happens in telophase 1?
Chromosomes assemble at each pole, nuclear membrane reforms, chromosomes uncoil.
Cell undergoes cytokinesis & reduction from diploid to haploid is complete.
What happens in prophase 2?
Chromosomes condense and become visible again. Nuclear envelope breaks down, spindle formation begins.
What happens in metaphase 2?
Individual chromosomes assemble on metaphase plate (same as mitotic), independent assortment / genetic variation again due to crossing over.
What happens in anaphase 2?
Individual chromosomes are pulled to opposite poles after the centromeres divide.
What happens in telophase 2?
Chromatids assemble at poles as in mitotic telophase. Chromosomes uncoil and form chromatin again, nuclear envelope reforms, nucleolus becomes visible.
What happens in cytokinesis (meiosis)?
Cytokinesis forms 4 daughter cells - haploid due to the reduction division.
- genetically different to one another due to the independent assortment.
What is meant by reduction division?
Gametes must contain half the diploid number of chromosomes so as to prevent an increase in chromosome number beyond the diploid number in the zygote.
Two divisions in cells produces 4 daughter cells (gametes) with each containing half the chromosome number of the parent cell.
What are homologous pairs of chromosomes?
Pairs of chromosomes in a diploid organism - one inherited from the mother and one from the father.
What are sister chromatids?
Two identical copies of a chromosome produced after DNA replication - joined at the centromere.
