Meiosis (Eukaryotic Cell Division) Flashcards
Haploid vs Diploid
Haploid (n): one set of chromosomes (gametes)
Diploid (2n): two sets of chromosomes (somatic cells)
What phases come under Meiosis 1?
Prophase 1, Metaphase 1, Anaphase 1, Telophase 1 and Cytokinesis
What happens in Prophase 1?
Homologous chromosomes align and synapse, crossing over between non-sister chromatids occurs at the chiasmata, crossing over now results in chromatids being a mix of pieces from each homologous chromosome
What happens in Metaphase 1?
Paired homologous chromosomes move to the metaphase plate, Chiasmata (not kinetochores as in Mitosis) line up on the metaphase plate.
What happens in Anaphase 1?
Recombined homologous chromosomes separate (disjoin), sister chromatids remain attached (whereas in mitosis sister chromatids separate)
What happens in Telophase 1 and Cytokinesis?
Haploid cells with duplicated chromosomes (the pairs of sister chromatids) form. Haploid because only half the genetic information is in each new cell.
Cleavage furrow forms and the two daughter cells are made
What are the crucial differences between mitosis and meiosis?
Mitosis: chromosomes align independently, no chiasmata, centromeres on metaphase plate, chromatids disjoin, 2n –> 2n.
Meiosis: homologous chromosomes synapse, chiasmata, chiasmata on metaphase plate, chromosomes disjoin, 2n –> n.
Why is sexual reproduction worth it?
It produces genetic diversity
How does sexual reproduction produce genetic diversity?
- Through independent assortment of chromosomes
- Crossing over
- RANDOM fertilisation of gametes
Genetic diversity allows selective responses. Why?
For example to:
- spatially variable environments (eg climate, ecology)
- changing environments (eg. parasites, seasons)
- sib-sib competition
What is segregation?
How the alleles of each gene are separated into the 4 meiosis daughter cells at the end of Meiosis 1. Results in more variation bc it is random.
What is independent assortment?
How the pairs of homologous chromosomes line up on the equator of the cell results in different arrangements of what gets into the two cells formed at the end of Meiosis 1. Results in more variation bc it is random.
What is the equation to work out how many possibilities there are for the possible gametes?
2^n
What is crossing over?
Happens during Prophase 1 when the homologous chromosomes align and synapse. The two non-sister chromatids swap parts of their DNA that are touching each other, creating more variation.
What happens in Meiosis 2?
The separation of sister chromatids. This occurs exactly the same way as mitosis but the result is 4 haploid daughter cells that contain just one copy of DNA. The names for the phases all have a 2 after them to signal that they happen in Meiosis 2.
