Genetics of living systems

Question 1

What is a mutation

Answer 1

change in the base sequence of bases in DNA

Question 2

Substitution

Answer 2

one nucleotide is substituted and changes the codon in which it occurs which leads to a change in the primary structure of the protein
(however, the degenerate code means that sometimes substitution wont alter the protein as the codon still codes for the correct amino acid)

Question 3

Deletion

Answer 3

one nucleotide is deleted out of the sequence and leads to a frameshift and as the chain is read in triplets this will change every successive codon from the point of mutation

Question 4

Insertion

Answer 4

one extra nucleotide is added and leads to a frameshift

Question 5

Mutations with no effect

Answer 5

there is no effect on the phenotype of the organism because normally functioning proteins are still synthesised

Question 6

Mutations that are damaging

Answer 6

the phenotype of an organism is affected in a negative way because proteins are no longer synthesised or are non-functional

Question 7

Mutations that are beneficial

Answer 7

rarely a protein is synthesised that results in a new and useful characteristic in the phenotype (e.g a mutation present in the proteins in the cell membrane of human cells means that HIV cannot enter these cells so those with this mutation are immune to the virus)

Question 8

Spontaneous mutations

Answer 8

occur during DNA replication, but the rate of mutation is increased by mutagens

Question 9

Mutagens

Answer 9

chemical, physical or biological agents which cause mutations

Question 10

Loss of bases

Answer 10

Loss of purine or pyrimidine bases can lead to the incorrect base being inserted through complementary base pairing

Question 11

Free radicals

Answer 11

oxidising agents that can affect the structures of nucleotides and disrupt base pairing during DNA replication

Question 12

Antioxidants

Answer 12

are anticarcinogens as they negate the effects of free radicals

Question 13

Physical mutagen

Answer 13

ionising radiation like X-rays - breaks DNA strands and mutations occur when they are fixed

Question 14

Chemical mutagen

Answer 14

deaminating agents - chemically alter bases of DNA such as converting cytosine to uracil in DNA (uracil usually binds to adenine)

Question 15

Biological mutagen

Answer 15

viruses - insert their genome and change the base sequence

Question 16

Beneficial mutation

Answer 16

Ability to digest lactose is thought to be a recent mutation, the majority of humans become lactose intolerant after they cease to be breastfed. The ability for us to drink milk decreases the likelihood of getting diseases such as osteoporosis

Question 17

Chromosome mutations

Answer 17

affect the whole chromosome or a number of chromosomes within a cell

Question 18

Causes of chromosome mutations

Answer 18

Can occur normally during meiosis
Can be caused by mutagens
Often are silent but can lead to developmental difficulties

Question 19

Deletion

Answer 19

Section of chromosome breaks off and is lost within a cell

Question 20

Duplication

Answer 20

sections on the chromosome get duplicated

Question 21

Translocation

Answer 21

one section of one chromosome breaks off and joins another non-homologous chromosome

Question 22

Inversion

Answer 22

a section of chromosome breaks off, is reversed and then joins back onto the chromosome