meiosis Flashcards
sexual life cycles ( stages in reproductive history of an organism)
- meiosis, gamete production, fertilisation
- meiosis alternates with fertilisation = genetic variation
2n->meiosis->n->fertilisation->2n - meiosis chromosome diploid 2n -> haploid n
how meiosis reduces chromosome number
- interphase = homologous pair of chromosomes replicate (individual chromosome from each parent) I I -> XX
- meiosis I = homogulous choromsomes separate X X
- meiosis II = sister chromatids separate I I I I
Meiosis I stages
Prophase I
metaphase I
anaphase I
Telophase I
meiosis II stages
Prophase II
Metaphase II
Anaphase II
telophase II
prophase I
90%
- synapsis - homologous chromosomes pair together
2. crossing over between homologues at chiasmata (exchange of genetic information)
metaphase I
- chromosomes on metaphase plate in homologous pairs
2. kinetichore microtubules attach to 1 chromosome of each pair
anaphase I
- homologous chromosomes separated
- spindles pull chromosomes to poles
- sister chromatids remain attached (single unit)
Telophase I and cytokinesis
- = 2 daughter cells
2. no more replication of DNA
Metaphase II
chromosomes on metaphase plate -> same as mitosis
Anaphase II
centromeres separate. sister chromatids move away
Telophase II and cytokineses
separate nuclei form. cytokinesis occurs
4 haploid daughter cells
meiosis I vs mitosis
- synapsis allows crossing over of non sister chromatids
- homologues align on metaphase plate
- homologues separate (sister chromatids do not)
genetic variation
- independent assortment of chromosomes
- crossing over
- random fertilisation
independent assortment of chromosomes
orientation of homologous pairs on metaphase plate is random
