Genetic Diversity & Natural Selection

Question 1

define mutation

Answer 1

a random change in the base sequence of DNA, resulting in the formation of a new allele

Question 2

define allele

Answer 2

a different version of the same gene

Question 3

how can a mutation have a knock on effect on the creation of a protein? (3)

Answer 3

• a mutation in DNA may change the primary structure of a polypeptide
• this would then change the position of the bonds between R groups, changing the tertiary structure of the polypeptide
• this may make the protein non-functional

Question 4

how many types of mutations are there?

what are they known as?

Answer 4

four

• substitution mutations
• addition and deletion mutations
• duplication mutations
• inversion mutations

Question 5

what does a substitution mutation involve?

Answer 5

changing one base in a DNA triplet

Question 6

what is the consequence of a substitution mutation occurring? (2)

Answer 6

through the changing of a DNA base,

• the corresponding base within an mRNA codon is then changed
• which means that only one amino acid is potentially changed in the primary structure of a polypeptide

Question 7

what can substitution mutations also be known as?

Answer 7

point mutations

Question 8

what does an addition and deletion mutation involve?

Answer 8

adding or deleting DNA nucleotide bases

Question 9

what is the consequence of an addition and deletion mutation occurring? (2)

Answer 9

through adding or deleting DNA nucleotide bases,

• there is an alteration of the base triplets and codons following the site of mutation
• this then changes the primary structure and therefore changes the tertiary structure of the polypeptide

Question 10

what can an addition and deletion mutation also known as?

Answer 10

a frame shift

Question 11

all mutations can be good and bad, in terms of their effects

how can a mutation be good for an organism? (2)

Answer 11

• an enzyme can become more complementary to the substrate
• an organism can have increased survival / reproductive processes

Question 12

all mutations can be good and bad, in terms of their effects

how can a mutation be bad for an organism?

Answer 12

• an enzyme can become less complementary to the substrate

Question 13

what are mutagenic agents

Answer 13

factors that increase the rate of gene mutations

Question 14

list the common mutagenic agents (3)

Answer 14

• high energy radiation
• carcinogens
• biological agents (such as viruses)

Question 15

meiosis (3)

Answer 15

the production of four haploid cells from a single diploid parent cell

• produce daughter cells that are genetically different from one another
• this includes gametes such as egg cells, sperm cells and pollen (in plants)

Question 16

outline what a diploid cell is

Answer 16

a cell that contains a pair of homologous chromosomes that carry the same genes

Question 17

outline what a haploid cell is

Answer 17

a cell that has half the number of chromosomes

Question 18

prior to meiosis… (2)

Answer 18

• interphase takes place
• semi conservative replication creates a copy of each chromosome - they now comprise of sister chromatids

Question 19

how many nuclear divisions occur within meiosis?

Answer 19

two nuclear divisions

• meiosis 1
• meiosis 2

Question 20

list the four phases of meiosis 1

Answer 20

prophase 1
metaphase 1
anaphase 1
telophase1

Question 21

prophase 1 (5)

Answer 21

where CROSSING OVER can occur

• homologous pairs of chromosomes associate
• chiasmata form, whereby non sister chromatids wrap around one another
• equal lengths of non sister chromatids are exchanged
• this produces new combinations of alleles

Question 22

metaphase 1 (3)

Answer 22

where INDEPENDENT SEGREGATION occurs
the random shuffling or assortment of homologous chromosomes

• homologous pairs will align at the equator of the cell
• they can be on any one side of each other when this occurs

Question 23

anaphase 1 (2)

Answer 23

• each pair of homologous chromosomes are separated ; maternal and paternal chromosomes will move to opposite poles
• this leads to a reduction in the number of chromosomes ; they are halved

Question 24

telophase 1

Answer 24

• the first nuclear division
• creates two haploid cells

Question 25

list the four phases of **meiosis 2**

Answer 25

prophase 2 metaphase 2 anaphase 2 telophase 2

Question 26

what is the purpose of **meiosis 2** (2)

Answer 26

**essentially the same as mitosis** - to pull sister chromatids apart and move them to opposite poles of the cell - this *happens in both cells* and so *produces four haploid cells*

Question 27

what is the consequence of a **nondisjunction mutation** occurring?

Answer 27

the daughter cells produced will contain either an extra chromosome (n + 1) or lack a chromosome (n + 2)

Question 28

during meiosis 1, a nondisjunction mutation involves...

Answer 28

the homologous chromosomes not separating correctly during anaphase 1

Question 29

during meiosis 2, a nondisjunction mutation involves...

Answer 29

the sister chromatids not splitting correctly