Meiosis + genetic variation

Question 1

What does meiosis produce?

Answer 1

four haploid daughter cells that are genetically different from each other from single diploid parent cell

Question 2

What happens in interphase?

Answer 2

G1 = synthesis of proteins and other biological molecules
S = DNA replication
G2 = assembly of organelles and checking
- chromosome is chromatin

Question 3

What happens in Prophase 1?

Answer 3

• nuclear envelope is breaking down
• chromosomes are condensing (becoming shorter and fatter), now two sister chromatids
• centrioles and spindle fibres appear

Question 4

What happens in metaphase 1?

Answer 4

• the chromosomes arrange themselves into homologous pairs and line up along the equator
• where crossing over will occur

Question 5

What happens in anaphase 1?

Answer 5

• spindle fibres contract
  = one from each homologous pair is pulled to opposite poles
• halving the chromosome number

Question 6

What happens in telophase 1?

Answer 6

• nuclear envelope reforms
• spindle fibres disintegrate
• cytokenesis

Question 7

What happens in prophase 2?

Answer 7

• nuclear envelope breaks down
• chromosomes condense
• now sister chromatids

Question 8

What happens in metaphase 2?

Answer 8

sister chromatids line up along the equator attached to the spindle fibres via the centromere

Question 9

What happens in anaphase 2?

Answer 9

• spindle fibres contract and pull sister chromatids apart at the centromere (centromere divides)
• now called chromosomes

Question 10

What happens in telophase 2?

Answer 10

• nuclear membrane reforms
• produces 4 daughter cells each with 2 chromosomes

Question 11

How is variation introduced?

Answer 11

• independent segregation of homologous chromosomes
• crossing over between homologous chromosomes
  → both occur in first round of division
• random fertilisation

Question 12

How does independent segregation increase variation?

Answer 12

• it is random which side of the equator the paternal and maternal chromosome lie
• those pairs are separated so one of each homologous pair ends up in each daughter cell - it is random which chromosome from each pair ends up in which daughter cell
  → large number of possible combinations of chromosome in daughter cells produced

Question 13

How does crossing over increase variation?

Answer 13

• chromatids twist around each other and parts of the chromatid swap
  → results in same gene with different combination of alleles
• chromatids twisting around each other can put tension on chromatids and parts break and broken parts can recombine with another

Question 14

How can random fertilisation increase variation?

Answer 14

• it is random which egg and sperm fuse in fertilisation
• produces zygotes with different combination of chromosomes → mixing of genetic material increases genetic diversity

Question 15

How is meiosis different to mitosis?

Answer 15

• Meiosis involves two nuclear divisions but mitosis involves one
• Meiosis introduces genetic variation and daughter cells are genetically different from each other and parent cell but mitosis creates genetically identical cells
• Meiosis produces cells with half the number of chromosomes as the parent cell (haploid) but mitosis produces cells with same number of chromosomes as parent cell (diploid)
• meiosis produces four daughter cells but mitosis produces two daughter cells