meiosis

Question 1

what is meiosis ?

Answer 1

a type of cell division

Question 2

what are the features of the 4 haploid cells ?

Answer 2

meiosis produces daughter cells that are genetically different from eachother ( gametes )

Question 3

how many divisions does meiosis involve ?

Answer 3

meiosis involves 2 nuclear divisions

Question 4

what does meiosis create ?

Answer 4

4 haploid daughter cells from a single diploid parent

Question 5

what are the 2 mechanisms in meiosis which introduce variation ?

Answer 5

• independent segregation of homologous chromosomes
• genetic recombination ( crossing over between homologous chromosomes )

Question 6

when does independent segregation and genetic recombination happen ?

Answer 6

both occur in meiosis 1
- in the first round of division

Question 7

during which stage does independent segregation occur ?

Answer 7

in metaphase 1

Question 8

during which stage does genetic recombination occur ?

Answer 8

in prophase 1

Question 9

state what happens in independent segregation ?

Answer 9

• homologous pairs of chromosomes line up opposite each other at the equator of the cell
• these pairs are then separated, so one of each homologous pair ends up in the daughter cell

Question 10

which side of the equator will the paternal and maternal chromosomes from each homologous pair lie ?

Answer 10

it is random

Question 11

what does independent segregation create in terms of possible combinations of chromosomes ?

Answer 11

this creates a large number of possible combinations of chromosomes in the daughter cells produced

Question 12

how can the possible combinations of chromosomes in independent segregation be calculated ?

Answer 12

2^n
n = number of pairs of chromosomes (homologous pairs)

Question 13

work out the possible combination of chromosomes in independent segregation in a human gamete ?

Answer 13

2^23
= 8,388,608 possible combinations

Question 14

quick summary of independent segregation ?

Answer 14

maternal and paternal chromosomes are reshuffled into any combination when forming homologous pairs in metaphase 1

Question 15

summary of genetic recombination ?

Answer 15

• when homologous pairs line up opposite each other at the equator in prophase 1, parts of the chromatids can become twisted around each other
• this puts tension on the chromatids, causing pairs of the chromatid to break
• the broken parts of the chromatid recombine with another chromatid
• they swap section of the chromatids

Question 16

what does genetic recombination result in ?

Answer 16

it results in a new combination of alleles

Question 17

compare meiosis with mitosis (3)

Answer 17

meiosis
- 2 nuclear divisions
- haploid cells produced
- introduces genetic variation

mitosis
- 1 nuclear division
- diploid cells are produced
- create genetically identical cells

Question 18

what does meiosis involve ?

Answer 18

meiosis involves a diploid (2n) parent cell dividing to become a haploid (n) cell

Question 19

what is meant by the final increase in genetic variation once meiosis has occurred ?

Answer 19

random fertilisation further increases genetic variation
- it is random which egg and sperm will fuse in fertilisation so variation is increased

Question 20

how many possible combination of chromosomes are there when you consider random fertilisation ?

Answer 20

(2^n)^2 possible combinations of chromosomes

• this is before crossing over is considered

Question 21

what does meiosis result in ?

Answer 21

genetic variation