Topic 27: Meiosis Flashcards
Describe the role of Meiosis in the human life cycle.
The role of Meiosis in the human life cycle is to produce 4 gametes cells from one diploid cell.
Describe the events that occur in each phase of Meiosis. Draw Meiosis for a cell that has a ploidy of 2n=8
**Meiosis 1
Interphase: In this phase the cell goes through the three stages where DNA is duplicated and the cell is checked.
Prophase 1: The nucleus is broken down and homologous pairs of the diploid cell where synapsis and crossing over of genetic information occurs.
Metaphase 1: The recombinant homologous pairs line up forming a tetrad in the center of the cell.
Anaphase 1: The recombinant homologous pairs are seperated from eachother and the special tetrads break apart.
Telophase and Cytokinesis: The cell rebuild the nucleus and two haploid cells are formed.
**Meiosis 11 **
Prophase 11: The nucleus is broken down once more and now we have sister chromatids.
Metaphase 11: The sister chromatids line up in the center of the cell.
Anaphase 11: The sister chromatids are now seperated on opposite sides.
Telophase 11 and Cytokinesis: The nucleus begins to reform ro each chromosome and four haploid cells are formed, unique from one another.
Understand how Meiosis produces haploid cells. Compare Meiosis 1 versus Meiosis II
In meiosis a single diploid cell forms 4 unique haploid cells called gametes. Meiosis is broken down into two parts.
**Meiosis 1 **
The diploid cell is divided into 2 haploid cells. Before cell division interphase does occur, where DNA is duplicated and cells undergo G1 phase, S phase, and G2 phase.
Then the cell starts meiosis where it enter Prophase 1, Metaphase 1, Anaphase 1, and Telophase 1 and Cytokinesis.
The difference in Meiosis 1 is that it begins with a diploid cell and ends into two haploid cell. The homologous chromosomes also cross over resulting in recombinated chromosomes. In Anapphase we also have homologous chromosomes being seperated into sister chromatids.
Meiosis 2
Now our 2 haploid cells undergo cell division. Now the sister chromatids are lined up in Metaphase and dividing in Anaphase. We end up with four unique haploid cells 2 with nonrecombinant chromosomes and 2 with recombinant chromosomes.
Meiosis 2 is very similar to Mitosis.
Describe the three events that occur in Meiosis but not Mitosis when do they happen?
Three events that occur in Meiosis but not in Mitosis are homologous chromosomes pair up, crossing over or synapsis occurs in Prophase 1, and homologus lined up as tetrads in Metaphase 1.
Explain crossing over and identify when it happens in meiosis.
Crossing over is the process when two homologus pairs one paternal and one maternal interatct with one another. The chromsosme share DNA by wrapping around eachother cutiing their own DNA and placing back onto the opposite chromosome.
Crossing over or Synapsis occurs in Prophase 1.
Describe the mechanisms that lead to genetic diversity in Meiosis and fertilization.
Mechanisms that lead to diversity in Meiosis is independent assortment of chromsomes (how they line up as tetrads in Metaphase 1), crossing over. and random fertilization (the different gametes made by different combination make a zygote).
