2.3.3 Meiosis and Mitosis Flashcards
How many chromosomes make up human cells?
Human cells contain 46 chromosomes, made up of 22 homologous pairs and a pair of sex chromosomes
What happens when a sperm and ovum fuse?
the full number of chromosomes are restored (46)
Where does meiosis occur?
In the ovaries or testes
What is produced during meiosis?
Haploid cells are produced
Describer the process of meiosis
- Chromosomes replicate, producing chromosomes made up of 2 chromatids
- Meiosis I - Homologous chromosomes pair up and divide
- Meiosis II - Chromatids separate and gametes are formed
What do haploid cells allow to happen?
Haploid cells help create genetic variation
What is independent assortment?
The process of lining up of a chromosome pairs at random. This means there could be several combinations of haploid cells
What is crossing over?
During meiosis I, all four chromatids come into contact and break and rejoin at these points
What do we call the part of the chromatid where it breaks and rejoins?
Chiasma
Describe what happens at interphase
- G1 - DNA polymerase is switched on, preparing the cell for division
- S - DNA pol. synthesis the DNA
- G2 - Cell prepares for mitosis
What happens at prophase?
- DNA condenses
- Chromatids are visible and joined at centromere
- Microtubules form the spindle
- Centrioles move to opposite ends of the nuclear envelope, forming two spindles
What happens at metaphase?
- Nuclear envelope starts to break down
- Chromatids align down the middle of the cell
- Spindle fibres attach to the centromeres
What happens at anaphase?
- Spindle fibres shorten, causing centromeres to split
- The stage ends when spindle breaks down
What happens to telophase?
- Chromosomes unravel
- Nuclear envelope reforms
What is cytokinesis?
The nuclear envelope meets in the middle, splitting the two cells
