2.3b - Meiosis Flashcards
Meiosis is…
the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte
In diploid cells, chromosomes typically appear as…
homologous pairs
Homologous chromosomes are…
chromosomes of the same size, same centromere position and with the same sequence of genes at the same loci
2 Meiosis stages
Meiosis I and Meiosis II
Meiosis I - Stage 1
The same chromosomes, which have replicated prior to meiosis 1, each consist of two genetically identical chromatids attached at the centromere
Meiosis I - Stage 2
The chromosomes condense and the homologous chromosomes pair up
Meiosis I - Stage 3
Chiasmata form at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged. Linked genes are those on the same chromosome. Crossing over can result in new combinations of the alleles of these genes.
Meiosis I - Stage 4
The crossing over of DNA is random and produces genetically different recombinant chromosomes
Meiosis I - Stage 5
Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle
Meiosis I - Stage 6
The orientation of the pairs of homologous chromosomes at the equator is random. Each pair of homologous chromosomes is positioned independently of the other pairs, irrespective of their maternal and paternal origin. This is known as independent assortment.
Meiosis I - Stage 7
The chromosomes of each homologous pair are separated and move towards opposite poles
Meiosis I - Stage 8
Cytokinesis occurs and two daughter cells form
Meiosis II
Each of the two cells produced in meiosis I undergoes a further division during which the sister chromatids of each chromosome are separated. A total of four haploid cells are produced.
