Unit 2 - Topic 3 - Variation and Sexual Reproduction - Section B - Meiosis Flashcards
What is meiosis
Meiosis is the division of the nucleus that results in the formation of haploid gametes from a diploid gametocyte
How do chromosomes appear in diploid cells
As homologous pairs
What are homologous chromosomes
chromosomes of the same size, same centromere position and with the same sequence of genes at the same loci
How many stages are in meiosis
2 - Meiosis I and Meiosis II
Describe the first step of meiosis I
The chromosomes, which have replicated prior to meiosis I, each consist of two genetically identical chromatids attached at the centromere
Describe step 2 of meiosis I
The chromosomes condense and the homologous chromosomes pair up
Describe step 3 of meiosis I
Chiasmata form at points of contact between the non-sister chromatids of a homologous pair and sections of DNA are exchanged
What are linked genes and what does crossing over do with them
Genes on the same chromosome. Crossing over can result in new combinations of the alleles of these genes.
What is this crossing over of DNA
Random and produces genetically different recombinant chromosomes
Describe step 4 of meiosis I
Spindle fibres attach to the homologous pairs and line them up at the equator of the spindle
What is independent assortment
Each pair of homologous chromosomes is positioned (randomly at the equator) independently of the other pairs, irrespective of their maternal and paternal origin.
Describe step 5 of meiosis I
The chromosomes of each homologous pair are separated and move towards opposite poles
Describe the final step of meiosis I
Cytokinesis occurs and two daughter cells form
Describe 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
What is produced at the end of meiosis II
A total of 4 haploid cells
