Meiosis

Question 1

What is meiosis?

Answer 1

Type of cell division in which a parent cell divides to form 4 haploid cells each genetically distinct from one another

Question 2

What happens before meiosis can begin?

Answer 2

DNA is replicated during interphase so each chromosome contains 2 chromatids

Question 3

What are the 2 divisions of meiosis?

Answer 3

Meiosis I = homologous chromosomes are separated
Meiosis II = chromatids are separated

Question 4

What does meiosis produce?

Answer 4

Reduction division where chromosome number is halved to form haploid cells which form gametes (egg and sperm cells) in animals and plants

Question 5

What happens in the 2 divisions of meiosis?

Answer 5

Meiosis I = prophase I, metaphase I, anaphase I, and telophase I
Meiosis II = prophase II, metaphase II, anaphase II, and telophase II

Question 6

What happens during prophase I?

Answer 6

• chromosomes condense and homologous chromosomes pair up
• centrioles migrate to opposite poles where each centriole starts forming spindle fibres
• nucleolus disappears and nuclear envelope breaks down leaving the chromosomes free in cytoplasm

Question 7

What happens during metaphase I?

Answer 7

• chromosomes line up along cell equator in their homologous pairs
• each chromosome attaches to the spindle by their centromere

Question 8

What happens during anaphase I?

Answer 8

Homologous chromosome pairs are separated and pulled to opposite poles of the cell (chromatids stay joined together)

Question 9

What happens during telophase I?

Answer 9

• chromosomes reach opposite poles of cell where they uncoil
• nuclear envelope forms around each set of chromosomes and the nucleolus starts to reform.
• cytoplasm divides to form two cells (cytokinesis)

Question 10

What happens during prophase II?

Answer 10

• chromosomes condense and are now visible under microscope
• centrioles migrate to opposite poles where each centriole starts forming spindle fibres.
• nucleolus disappears and the nuclear envelope starts to break down

Question 11

What happens during metaphase II?

Answer 11

• chromosomes line up at the equator of the cell
• each chromosome attaches to the spindle by their centromere

Question 12

What happens during telophase II?

Answer 12

• chromatids reach opposite poles of the cell where they uncoil to become long and thin again
• nuclear envelope forms around each set of chromosomes to form two nuclei and the nucleolus starts to reform
• cytoplasm divides (cytokinesis) and 4 cells are produced

Question 12

What happens during anaphase II?

Answer 12

• centromeres divide and separate each pair of chromatids
• spindle fibres contract and shorten to pull the chromatids to opposite poles

Question 13

What is the importance of meiosis?

Answer 13

Haploid gametes production = allows sexual reproduction to occur
Genetic variation = increases diversity allowing natural selection to occur

Question 14

What is meiosis and why is it needed?

Answer 14

Sexual reproduction two gametes (sex cells) fuse together to form a zygote

needed to produce haploid gamete cells containing only half the number of chromosomes as a body cell

Question 15

What does a zygote contain?

Answer 15

Diploid number of chromosomes (2n), half of these chromosomes are from the father’s sperm cell and half are from the mother’s egg cell

Question 16

What 2 events in meiosis lead to genetic variation?

Answer 16

• Independent segregation (random assortment)
• crossing over

Question 17

When does crossing over occur?

Answer 17

Prophase 1 of meiosis

Question 18

What are the stages of crossing over?

Answer 18

1) homologous chromosomes condense and pair up
2) chromatids of each chromosome twist around one another forming a chiasmata
3) when chromosomes are separated during anaphase I chromatids break at the chiasmata and reconnect to the chromatid from the homologous chromosome

Question 19

What does crossing over allow?

Answer 19

Swaps alleles between the homologous chromosomes to produce different combinations on each chromosome producing 4 genetically different daughter cells

Question 20

When does independent segregation/assortment occur?

Answer 20

Metaphase I

Question 21

What happens during independent segregation/assortment?

Answer 21

Homologous chromosomes line up along the cell’s equator

whether paternal or maternal chromosomes appears on the left or right is completely random as a result, which chromosomes end up in each daughter cell is also random

Question 22

What is the equation to calculate genetic variation?

Answer 22

2n where ‘n’ represents number of chromosome pairs