3.4.3 mutation and 3.4.4 natural selection

Question 1

allele

Answer 1

different version of the same gene

Question 2

mutation

Answer 2

change in the base sequence of DNA

Question 3

types of mutation

Answer 3

substiution, deletion, addition + insertion

Question 4

silent mutation

Answer 4

as the genetic code is degenerate a change in the base sequence may still cause the correct amino acid to be coded for

Question 5

why is deletion more likely to result in a mutation

Answer 5

deletion causes a frame shift in all triplets.
therfore all codons are affected
this changes all the amino acids coded for

Question 6

why is substitution less likely to result in a mutation

Answer 6

only one base is affected, no frame shift
less severe effect on the polypeptide

Question 7

mutagenic agents

Answer 7

agents that increase rate of mutation

Question 8

chromosme mutation

Answer 8

changes in the structure or numbers of chromosomes

Question 9

non-disjunction

Answer 9

failure of chromosome to seperate during meiosis

Question 10

products of meiosis

Answer 10

4 genetically different haploid daughter cells

Question 11

what occurs in meiosis 1

Answer 11

division of homologous chromosomes

Question 12

what occurs in meiosis 2

Answer 12

division of sister chromatids

Question 13

prophase 1

Answer 13

chromosomes condense + homologous chromosomes pair up.
centrioles move to opposite ends of the cell forming spindle fibres.
nucleolus disappears and nuclear envelope breaks down.

Question 14

metaphase 1

Answer 14

chromosomes line up along the equator of the cell.
spindle fibres attach to the centromere of the chromosome

Question 15

anaphase 1

Answer 15

homologous chromosomes are separated and pulled apart to opposite ends of the cell

Question 16

telophase 1

Answer 16

chromosomes uncoil
nuclear envelop reforms around each set of chromosomes and nuclear envelope starts to reform
cytoplasm divides

Question 17

prophase 2

Answer 17

chromosomes condense and are now visible
centrioles move to opposite ends of the cell forming spindle fibres

Question 18

metaphase 2

Answer 18

chromosomes line up along the equator of the cell.
spindle fibres attach at the centromere of the chromosome

Question 19

anaphase 2

Answer 19

centromeres pull apart each pair of the sister chromatids.
spindle fibres pull apart the chromatids to opposite ends of the cell

Question 20

telophase 2

Answer 20

chromatids reach the opposite ends of the cell where they uncoil.
nucleolus and nuclear envelope reform.
cytoplasm divides

Question 21

homologous chromosomes

Answer 21

one paternal and one maternal pair of chromosomes

Question 22

how does meiosis lead to genetic variation

Answer 22

crossing over
independent segregation

Question 23

crossing over

Answer 23

during prophase 1.
homologous chromosomes pair up.
the chromatids of each chromosome twist around each other forming a chiasmata.
forming new combinations of alleles.

Question 24

independent segregation

Answer 24

during metaphase 1.
homologous chromosomes are randomly separated.
so which chromosomes ends up in each daughter cell is completely random.
therefore each daughter cell will have a different combination of daughter cells.

Question 25

3 differences between the outcome of mitosis and meiosis

Answer 25

meiosis produces haploid cells, mitosis produces diploid cells
meiosis produces genetically different cells, mitosis produces genetically identical cells
meiosis produces 4 daughter cells and mitosis produces 2 daughter cells

Question 26

how does random fertilisation increases genetic variation

Answer 26

fertilisation is a random event, any sperm can fuse with any egg

Question 27

Genetic diversity

Answer 27

Number of different alleles of genes in a population of a species

Question 28

How is genetic diversity increased

Answer 28

Mutations in DNA and gene flow (different alleles are introduced into the population due to migration)

Question 29

Why is it beneficial to have a high genetic diversity

Answer 29

Species are able to adapt to changes in the environment.

Question 30

Why may populations have low genetic diversity

Answer 30

Small population size, small number of individuals in the population, inbreeding

Question 31

Principles of natural selection

Answer 31

Random mutation produces new alleles
selection pressure means individuals with the new allele are at an advantage
they are more likely to survive and reproduce, passing on the advantageous alleles
over many generations the frequency of the advantageous allele increases

Question 32

behavioural adaption

Answer 32

ways organisms act to increase its chances of survival. e.g. playing dead

Question 33

physiological adaption

Answer 33

processes inside an organisms body to increase survival e.g. hibernation over winter to conserve energy

Question 34

anatomical adaption

Answer 34

structural feature to increase survival e.g. whales having thick layers of blubber to keep warm

Question 35

selection

Answer 35

process that results in the best adapted individuals in a population surviving to breed passing on the favourable allele onto the next generation

Question 36

directional selection

Answer 36

selection of one extreme phenotype.
graph shifts to the left or to the right.
directional selection changes the characteristics of the population

Question 37

stabilising selection

Answer 37

selection of non-extreme phenotypes, around the mean of a population.
stabilising selection preserves the characteristics of the population.
the graph shifts towards the centre becoming more narrow.

Question 38

antibiotic resistance

Answer 38

random mutation creates a resistant allele in the population.
when exposed to the antibiotic only those with the resistant allele survive and reproduce, passing on the resistant allele to the offspring.
overtime the frequency of the allele increases.