6.3 Meiosis Flashcards
Why is meiosis important ?
Formation of gametes ( haploid cells )
Genetic variation ( via independent assortment and crossing over )
List the stages of meiosis
Interphase Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2
Define the term homologous chromosomes
Matching sets of chromosomes
What happens in prophase 1?
Chromosomes condense
Nuclear envelope disintegrates
Nucleolus disappears
Spindle formation begins
Homologous chromosomes pair up, forming bivalents
Chromatids entangle ( crossing over )
What happens in metaphase 1?
Homologous pairs of chromosomes assemble along the equator
The orientation on the equator is random and independent ( independent assortment )
Chromosomes attached to spindle fibres at centromere
What happens in anaphase 1?
Homologous chromosomes pulled to opposite poles ( chromatids stay joined together )
Sections of DNA on sister chromatids which became entangled, break off and rejoin. The points where this happens is called chiasmata.
This forms recombinant chromatids.
What happens in telophase 1?
Chromosomes assemble at each pole
Nuclear membrane reforms
Chromosomes uncoil
Cell undergoes cytokinesis. Diploid is now haploid.
What happens in prophase 2?
Chromosomes ( still consist of two chromatids ) condense and become visible
Nuclear envelope breaks down
Spindle formation begins
What happens in metaphase 2?
Individual chromosomes line up along the equator
Crossing over means they are not identical so there is independent assortment again ( more genetic variation )
What happens in anaphase 2?
Individual chromosomes pulled to opposite poles after division of the centromeres
What happens in telophase 2?
Chromatids assemble at poles
Chromosomes uncoil and form chromatin
Nuclear envelope reforms
Nucleolus becomes visible
