6.3 Meiosis Flashcards
What are homologous chromosomes
When in chromosome pairs each nucleus of the organisms cells contains two full sets of genes (a pair of genes for each characteristic
What are alleles
Different versions of the same gene
What are the two main stages of meiosis
Meiosis 1 and meiosis 2
What happens during meiosis 1
The first division is the reduction division when the pairs of homologous chromosomes are separated into two cells. Each intermediate cell will only contain one full set of genes instead of two, so the cells are haploid
What happens during meiosis 2
The second division is similar to mitosis, and the pairs of chromatids present in each daughter cell are separated, forming two more cells. Four haploid daughter cells are produced in total
What happens during prophase 1
Chromosomes condense, the nuclear envelope disintegrates, the nucleolus disappears and the spindle formation begins. Homologous chromosomes pair up forming bivalents
What happens in metaphase 1
Bivalents orientate along the metaphase plate in homologous pairs. The homologous pairs are then attached to fibres from opposite poles. The sister chromatids attach to fibres from the same pole
What happens in anaphase 1
Homologous chromosomes are pulled to opposite poles and the chromatids joined to each other. The exchange of DNA takes place as sections of DNA on sister chromatids which became entangled in crossing over break off and then rejoin, sometimes resulting in the exchange of DNA
What happens in telophase 1
The chromosomes assemble at each pole and the nuclear membrane reforms as the chromosomes uncoil. This is the undergoing cytokinesis and dividing into two cells