3.3 Meiosis Flashcards
Explain mitosis.
You start with a cell with 2n/46 chromosomes.
Splits into 2 new cells which both have 2n, due to the S phase which causes the first cell to have 4n.
What is the function of meiosis?
To create reproductive cells. Sperm and egg cells
How does meiosis lead to genetic diversity?
- Fussion on gametes
- Crossing over
- Random orientation
What happens in meiosis 1?
- Prophase 1:
- Chromosomes are visible due to supercoiling.
- Crossing over at the chiasmata
- Spindle fibers start to form
- Metaphase 1:
- Random orientation towards the poles.
- Spindle fibers attach to the centromeres of the chromosomes, in order to align them along with the equatorial plate.
- Anaphase 1:
- Spindle microtubules shorten, pulling homologous chromosomes apart towards opposite poles.
- Telophase 1:
- Chromatids uncoil and nuclear membrane reforms.
- Cytokinesis occurs, resulting in two daughter cells.
What is the result of meiosis?
4 haploid cells
What is the chiasmata?
When the two legs of the homologous pairs attach and trade genes.
What is random orientation?
Maternal and paternal chromosomes do not have to line up on the same pole/sides.
What happens in meiosis 2?
- Prophase 2:
- Centrioles move to opposite poles
- Spindle fibers begin to form
- Nucleolus and nuclear membrane disintegrate
- Metaphase 2:
- Spindle fibers attach to centromeres, aligning the sister chromatids at the equator
- Anaphase 2:
- Centromeres divide
- Spindle fibers move chromatids to opposite poles
- Telophase 2:
- Formation of the nuclear envelope
- Cytokinesis takes place, resulting in 4 haploid cells
Explain the process of non-disjunction.
- Non-disjunction can occur in both Anaphase 1 and 2.
- The two chromatids do not separate, meaning that when the cell divides, one will have 4(or 2 if in anaphase 2), while the other has 0.
- Leading to non-disjunction
When does crossing over occur?
In prophase 1 of meiosis
What is the result of crossing over?
New combinations of alleles, contributing to genetic variations.
What are the ways of obtaining fetal materials for karyotyping?
- Amniocentesis
- Chorionic villus sampling
Explain Amniocentesis
- Performed between weeks 14 and 20 of pregnancy
- A needle is injected through the abdomen to withdraw a small amount of amniotic fluid
- Cells floating in the fluid are karyotyped
Explain chorionic villus sampling.
- Used between weeks 10-13 of pregnancy
- Suctioning tool is inserted through the vagina to reach the fetal cells in the chorion.
