meiosis

Question 1

what does meiosis produce?

Answer 1

gametes- produces 4 genetically different daughter cells

Question 2

what happens during prophase I?

Answer 2

chromosomes condense and become visible

nuclear envelope begins to break down

Question 3

what happens in metaphase I?

Answer 3

pairs of homologous chromosomes pair up along the equator (independent assortment)

crossing over occurs- bivalents- cross over at chiasmata

spindle fibres form and attach to centromeres

Question 4

what happens in anaphase I?

Answer 4

spindle fibres contract

chromosomes are pulled to opposite poles of cell- some of the chromatids are now recombinant

Question 5

what happens during telophase 1?

Answer 5

chromosomes decondense

nuclear envelope reforms

Question 6

what is formed at the end of the first division of meiosis?

Answer 6

two haploid cells formed each with 1 copy of each chromosome (maternal and paternal) but different combination of alleles

Question 7

what happens during prophase II?

Answer 7

chromosomes condense and become visible

nuclear membrane begins to break down

Question 8

what happens during metaphase II?

Answer 8

individual chromosomes line up along equator

spindle fibres form and attach to centromeres

Question 9

what happens during anaphase II?

Answer 9

spindle fibres contract

sister chromatids are pulled to opposite poles of the cell

Question 10

what happens during telophase II?

Answer 10

chromosomes decondense

nuclear envelope reforms

Question 11

what is formed after the second division of meiosis?

Answer 11

4 genetically different haploid cells

each gamete has unique combination of alleles and only single chromosome of maternal/paternal

Question 12

what is a bivalent?

Answer 12

chromosomes that are attached together in a homologous pair

Question 13

what is the chiasmata?

Answer 13

the point where chromatids from different chromosomes cross over

Question 14

why is the second division needed in meiosis?

Answer 14

to split the chromatids of each chromosome that were produced when the DNA was replicated

Question 15

what are the causes of genetic variation?

Answer 15

MEIOSIS- crossing over and independent assortment

random fertilisation

mutation

environmental factors

Question 16

describe how crossing over leads to genetic variation?

Answer 16

during metaphase I, homologous chromosomes pair up to form bivalents

the chromatids from different chromosomes in a pair cross over, the cross over point is called the chiasmata

genetic material is exchanged between the chromosomes

the chromatids from the different chromosomes in the pair carry the same genes but have different alleles

this means crossing over leads to new combinations of alleles

Question 17

describe how independent assortment leads to genetic variation?

Answer 17

the homologous pairs line up at the equator during metaphase I

the maternal and paternal chromosomes can line up on either side (it is random), the arrangement of one pair doesn’t influence arrangement of other pairs, they all line up independently of each other

at anaphase I, the chromosomes of homologous pairs are separated, each chromosome moves to opposite pole

this leads to new combination of alleles

Question 18

how do mutations cause genetic variation?

Answer 18

mutations are changes in base sequence of a gene

this created new alleles

Question 19

how does random fertilisation cause genetic variation?

Answer 19

any egg can be fertilised by any sperm

different combinations of alleles are brought together

Question 20

how do environmental factors lead to genetic variation?

Answer 20

affect expression of a gene in the phenotype

Question 21

where can mutations in number of chromosomes arise from?

Answer 21

spontaneously by chromosome non-disjunction during meiosis

Question 22

what is the mathematical formula for determining the number of possible combinations of chromosomes for each daughter cell of meiosis?

Answer 22

2^n where n is number of pairs of homologous chromosomes