B6 Meiosis (page 70) Flashcards
Gametes are produced by what?
Meiosis
What is Gametes?
they only have one copy of each chromosome, so that when gameete fusion takes place, you get the right amount of chromosomes again (two copies of each)
When gametes only have half the original number of chromosomes, what happens?
cells divide by Meiosis.
What is Meiosis?
This is a process that involves two cell divisions. In humans, it only happens in the reproductive organs (the overies in females and the testes in males)
Meiosis produces cells with half the normal number of chromosomes.
What is the process before Meiosis?
Before the cell starts to divide, it duplicates its genetic information, forming two armed chromosomes - one arm of each chromosome is an exact copy of the other arm. After replication, the chromosomes arrange themselves into pairs.
(replicatiion means the action of copying or reproducing something).
What happens in the first division in Meiosis?
the chromosome pairs line up in the centre of the cell.
The pairs are then pulled apart so each new cell only has one copy of each chromosome. Some of the father’s chromosomes, and some of the mother’s chromosomes, go into each new cell.
(see diagram on page 70).
What happens in the second division in Meiosis?
The chromosomes line up again in the centre of the cell. The arms of the chromosomes are pulled apart.
You get four gametes, each with only a single set of chromosomes in it. Each of the gametes is genetically different from the others because the chromosomes all get shuffled up during meiosis and each gamete only gets half of them, at random.
see diagram on page 70.
The cell produced by gamete fusion does what?
replicates itself.
After two gametes have fused during fertilisation what do this result in?
it results in new cell divides by mitosis to make a copy of itself.
Mitosis repeats many times to produce what?
lots of new cells in an embryo.
As the embryo develops, what do the cells then start to do?
they start to differentiate (see page 14), into the different types of specialised cell that make up a whole organism.
In humans, Meiosis only occurs in what for making gametes?
only occurs in the reproductive organs for making gametes.
Human body cells contain 46 chromosomes each. The graph on page 70 shows how the mass of DNA per cell changed as some cells divided by meiosis in human ovary. How many chromosomes were present in each cell when they reached stage 6? (1 mark)
23 (1 mark)
