Meiosis

Question 1

What are diploid cells?

Answer 1

• Cells that have two copies of each chromosome.

Question 2

What are haploid cells?

Answer 2

• Cells that have one copy of each chromosome.

Question 3

What are the daughter cells produced by meiosis like?

Answer 3

• Genetically different.
• Haploid daughter cells.
• 4

Question 4

How many nuclear divisions does meiosis include?

Answer 4

• Meiosis includes two nuclear divisions.

Question 5

What are the two mechanisms in meiosis that introduce variation? When do these two mechanisms actually occur?

Answer 5

• Independent segregation of homolgous chromosomes.
• Crossing over between homologus chromosomes.
• Two mechanisms occur in meiosis I.

Question 6

What is the idea of independent segregation?

Answer 6

• Homolgous pairs of chromosomes line up opposite each other at equator of cell.
• It is random which side of equator the paternal/ maternal homologous pairs lie.
• Homolgous pairs are separated, so one of each homologous pair ends up in daughter cell (after meiosis I- first round of division.)
• This creates large no of possible combinations of chromosomes in daughter cells produced.

Question 7

How many different combinations of chromsomes are there in the daughter cells produced by meiosis (only taking into account independent segeregation?)

Answer 7

2ⁿ
n = the number of homologous pairs of chromosomes.

Question 8

What is “crossing over?”

Answer 8

• Homologous pairs line up opposite each other at the equator in meiosis I, parts of chromatids can twist around each other.
• This puts tension on chromatids, causing pairs of the chromatid (on each homologous pair) to break.
• The broken parts of chromatid recombine with another chromatid.
• This results in new combinations of alleles.

Question 9

Give 3 differences between mitosis and meiosis.

Answer 9

• Meiosis = two nuclear division/ Mitosis = 1 nuclear division.
• Meiosis: daughter cells = haploid/ mitosis: daughter cells = diploid.
• Meiosis: introduces genetic variation (by crossing over and independent segregation.) Mitosis: creates genetically identical cells.

Question 10

How would we identify when meiosis occurs in the life cycle of an any organism (when given a diagram?)

Answer 10

• On diagram, when 2n (diploid cell) becomes n (haploid cell), this is the point at which meiosis has occurred.

Question 11

How is genetic variation increased (excluding independent segregation?)

Answer 11

• Random fertilisation will increase genetic variation even more.
• Random which egg/ sperm cell will fuse together.
• Therefore, possible combinations of chromosomes in daughter cells is actually (2ⁿ)² –> when you consider random fertilisation

Question 12

What formula will give the total possible combinations of chromosomes in daughter cells; taking into account: independent segreation and random fertilisation?

Answer 12

(2ⁿ)²

Question 13

Def of meiosis.

Answer 13

• Two nuclear divisions that result in the formation of four haploid daughter cells from a single diploid parent cell.

Question 14

How are genetically different daughter cells actually formed?

Answer 14

• Genetically different daughter cells from independent segregation of homologous chromosomes.

Question 15

What is a homologous pair of chromosomes?

Answer 15

• Homologous pair of chromosomes are exactly the same size, have exactly the same genes but may have different alleles.