3.4.3 - genetic diversity can arise as a result of mutation or during meiosis

Question 1

what do genetic mutations involve?

Answer 1

a change in the base sequence of chromosomes

Question 2

what are the features of genetic mutations?

Answer 2

1. they can arise spontaneously in DNA replication
2. they include base deletion and base substitution
3. not all base substitutions cause a change in they sequence of encoded amino acids, as the genetic code is degenerate (each amino acid coded by multiple codons)

Question 3

what do mutagenic agents do?

Answer 3

increase the rate of gene mutation

Question 4

what does meiosis do?

Answer 4

produce daughter cells that are genetically different from each other

Question 5

what happens overall during meiosis?

Answer 5

two nuclear divisions result usually in the formation of four haploid daughter cells from a single diploid parent cell

Question 6

what is a diploid cell?

Answer 6

one which contains pairs of chromosomes

Question 7

what is a haploid cell?

Answer 7

one which contains individual chromosomes

Question 8

what type of cell does meiosis 1 occur in?

Answer 8

a diploid cell

Question 9

what type of cell does meiosis 2 occur in?

Answer 9

a haploid cell

Question 10

how do chromosomes end up in a homologous pair?

Answer 10

one is from the mother, one is from the father
they contain the same gene eg. for blood group, but they may contain different alleles

Question 11

meiosis 1 - what happens in prophase 1?

Answer 11

chromosomes condense and become visible
homologous chromosomes link together (form chiasmata)
nuclear membrane breaks down, centrioles move to opposite poles of cell

Question 12

meiosis 1 - what happens in metaphase 1?

Answer 12

pairs of homologous chromosomes line up along the equator of the cell

Question 13

meiosis 1 - what happens in anaphase 1?

Answer 13

spindle fibres shorten pulling homologous chromosomes towards opposite poles of the cell

Question 14

meiosis 1 - what happens in telophase 1?

Answer 14

chromosomes reach poles of cell
nucelar membranes reform and chromosomes uncoil back to chromatin state
cytokinesis then occurs - cell divides into two haploid cells

Question 15

meiosis 2 - what happens in prophase 2?

Answer 15

chromosomes condense and become visible
nuclear membrane breaks down

Question 16

meiosis 2 - what happens in metaphase 2?

Answer 16

chromosomes line up along equator of cell

Question 17

meiosis 2 - what happens in anaphase 2?

Answer 17

spindle fibres shorten pulling chromatids towards opposite poles of cell
centromere of chromosomes divides

Question 18

meiosis 2 - what happens in telophase 2?

Answer 18

chromatids reach poles of cell
nuclear membranes reform
chromosomes uncoil back to chromatin state
cells undergo cytokinesis producing four haploid cells

Question 19

production of genetic variation - independent assortment?

Answer 19

when homologous chromosomes line up in metaphase 1, you can’t predict whether the maternal or paternal chromosome will end up in each resulting haploid cell

Question 20

production of genetic variation - crossing-over?

Answer 20

chromatids of two chromosomes in a homologous pair can wrap around each other - parts of each chromosome break off and exchange between the chromosomes (alleles swapped between them, which can occur multiple times)
bivalent = term for homologous chromosomes which have undergone crossing-over
chiasmata = point where chromatids join

Question 21

production of genetic variation - fertilisation?

Answer 21

during fertilisation, male and female haploid gametes randomly fuse together

Question 22

how do you calculate the possible number of different combinations of chromosomes following meiosis?

Answer 22

2^n
n = number of homologous chromosome pairs