4.6.1.2 Meiosis

Question 1

What does meiosis do to the number of chromosomes?

Answer 1

• meiosis halves the number of chromosomes in gametes
• fertilisation restores the full number of chromosomes when the gametes fuse/join

Question 2

How do cells in reproductive organs divide and why do they divide like that?

Answer 2

cells in reproductive organs divide by meiosis to form gametes

Question 3

How many chromosomes do gametes contain?

Answer 3

gametes only have 1 copy of each chromosome - 23 chromosomes, 23 chromatids

Question 4

What happens when a cell divides to form gametes?

Answer 4

• the cell makes copies of its chromosomes so it has double the amount of genetic information
• the cell divides into 2 cells each with half the amount of chromosomes - 23 chromosomes, 46 chromatids
• the cell divides for the second time (so twice) to form 4 gametes each with a single set of chromosomes (quarter of the amount of chromosomes) - 23 chromosomes, 23 chromatids
• all gametes are genetically difference from each other as crossing over takes place in meiosis (where chromosomes exchange genetic material between each other) - results in random chromosomes ending up in each of the 4 cells (gametes)

Question 5

What happens when gametes join/fuse at fertilisation?

Answer 5

• gametes join at fertilisation to restore the normal number of chromosomes
• the new cell divides by mitosis to produce many copies
• more and more cells are produced so the number of cells increases - embryo forms
• as they embryo develops cells differentiate to gain different structures that allow them to carry out different functions

Question 6

Diagram of meiosis:

Answer 6

Question 7

Phases of meiosis:

Answer 7

• Prophase 1
• Metaphase 1
• Anaphase 1
• Telophase 1
• Prophase 2
• Metaphase 2
• Anaphase 2
• Telophase 2