1.6 Mutation

Question 1

What is a mutation?

Answer 1

a mutation is an irreversible change in the genome resulting in no protein or a defective protein being produced

Question 2

What is a mutant?

Answer 2

a change in genotype due to a mutation causes a change in phenotype of the organism which is referred to as a mutant

Question 3

What is mutation the only source of?

Answer 3

genetic variation on which evolution depends on

Question 4

What are mutagenic agents?

Answer 4

The frequency of mutations (how often they occur) may be increased by mutagenic agents such as gamma rays, ultraviolet light, chemicals in cigarette smoke and mustard gas

Question 5

R O L F

Answer 5

Random
Occurence
Low
Frequency

Question 6

TOP TIP

Answer 6

Random mutation of genetic material within a cell is a source of genetic variation forms the bases of the processes of natural selection, speciation and evolution

Question 7

What are single gene mutations?

Answer 7

single gene mutations occur within genes and involve alterations of a DNA nucleotide/base sequence
Gene mutations result in no protein or an altered protein being produced

Question 8

TOP TIP

Answer 8

Single gene mutations are a bit like spelling errors in the genetic code

Question 9

What is insertion?

Answer 9

An additional base sequence into triplet of bases altering the base sequence of the gene from the point of the insertion
Many base triplets coding for many amino acids are affected causing a major change in the structure of the finished protein
this is a frameshift mutation

Question 10

What is deletion?

Answer 10

a base is deleted from a triplet of bases altering the base sequence from the point of the deletion, as all triplets move along one space to fill the gap
Many base triplets coding for many amino acids are affected causing a major change in the structure of the finished protein
this is a frameshift mutation

Question 11

What is substitution?

Answer 11

one base (nucleotide) within a triplet of DNA bases is substituted for another base, coding for one different amino acid in the polypeptide chain 
this causes a minor change to the finished protein

Question 12

Gorillas Dance In School

Answer 12

Genes
Deletion
Insertion
substitution

Question 13

What is a silent mutation?

Answer 13

a substituted nucleotide (base) results in a triplet that codes for the same amino acid and protein is normal

Question 14

What is a neutral mutation?

Answer 14

a substituted nucleotide (base) results in a triplet that codes for a different amino acid that is similar to the original and the mutated protein still functions normally

Question 15

What is a missense mutation?

Answer 15

A substituted nucleotide (base) results in a triplet that codes for a different amino acid which changes the function of the protein

Question 16

what is a nonsense mutation?

Answer 16

a substituted nucleotide (base) results in a stop codon so the polypeptide chain is shorter

Question 17

What is a splice site?

Answer 17

a mutation at a splice site may mean that some introns are not cut out of the primary mRNA transript
these introns will be read during translation and the protein will have extra amino acids which will after the structure and function of the protein

Question 18

What is a nucleotide sequence repeat?

Answer 18

a repeat expansion mutation can increase the number of times a short sequence of three or four base pairs is repeated
this can affect the function of a protein that is coded for a gene

Question 19

Example - Huntington’s disease (HD)

Answer 19

is caused by the expansion of a CAG DNA triplet repeat in a gene which codes for a protein protein whose absence can lead to the neurological degeneration linked to HD in humans

Question 20

Regulatory Sequence Mutations?

Answer 20

Some regions on chromosomes are regulatory genes
They may code for small repressor proteins that block the expression of genes. Their advantage is that they stop the production of large proteins when they are not needed, saving energy and resources

They may code for activators proteins that promote the transcription of genes

Mutation in regulator genes can change the expression of genes resulting in absent or excess proteins, changing the phenotype of the organism

such mutations may be lethal

Question 21

What is the significance of gene mutation in Evolution?

Answer 21

Point mutations are a source of variation
Occasionally the new form of the gene (allele) formed by the mutation can result can result in a protein that gives the organism a selective advantage
If this organism has a belter chance of surviving to reproduce the new alleles the new alleles will increase in frequency in the population

Question 22

What is chromosome structure mutation?

Answer 22

Where whole sections of chromosomes containing many genes are broken, rearranged or lost

Question 23

What is Deletion?

Answer 23

occurs when two breaks happen along the length of the chromosomes and the middle segment of chromosome with many genes is lost

Question 24

What is Inversion?

Answer 24

Occurs when two breaks happen along the length of the chromosome, the segment of chromosome between the breaks rotates 180 degrees and reattaches, reversing the gene sequence

Question 25

What is Duplication?

Answer 25

occurs when a broken segment from a homologous (a matching) chromosome is added, duplication a specific set of genes

Question 26

Duplicated Genes and evolution?

Answer 26

duplicated genes can undergo single gene mutations without affecting the functioning of the original copy
a new gene could then appear giving organism selective advantage without any effect on functioning of original gene

Question 27

What is translocation?

Answer 27

occurs when a segment breaks off the end of one chromosome and attaches to the end of a non homologous chromosome adding additional genes

Question 28

REMEMBER

Answer 28

in duplication the additional genes are from the homologous chromosome (so are the same); in translocation the additional genes are from a non homologous chromosome (so are different)

Question 29

Cats Do Dumps In Trays

Answer 29

Chromosome 
Deletion
Duplication
Inverison
Translocation

Question 30

What is polyploidy?

Answer 30

some cells can receive double the number of chromosomes usually present in the nucleus due to a fault that occurs during cell division
these cells have whole genome duplications and are called polyploid

Question 31

TOP TIP

Answer 31

haploid - single set of chromosomes - gametes

diploid - two sets of chromosomes - human somatic (body cells)

Question 32

Polyploidy in plants?

Answer 32

polyploidy in plants can be induced by heat or cold shock or by exposure to chemicals such as colchicine
polyploid plants are larger than normal plants and produce much larger fruits or seeds

Question 33

Polyploid human crops?

Answer 33

Because polyploid in plants are often larger, stronger and more productive than their diploid ancestors this can lead to humans bringing these species into cultivation
e.g. tomato and strawberry

Plant breeders have hybridised different species of wild ancestors to produce polyploid crop plants with vigorous growth and high yields
e.g. banana and potato

Question 34

Evolutionary significance of polyploidy in the production of food crops?

Answer 34

1. two wild ancestors of modern bread wheat hybridised naturally to produce a hybrid that had a selective advantage but was sterile
2. A chromosome mutation involving complete spindle failure during cell division doubled the chromosome number of the hybrid, making it fertile (polyploid)
3. The fertile hybrid is hybridised again with another wild grass. The offspring had selective advantage but was sterile
4. Again a chromosome mutation involving complete spindle failure during cell division doubled the chromosome number of the hybrid, making it the fertile bread wheat triticum vulgare which is so important for food security in many countries today

Question 35

Polyploidy in animals?

Answer 35

polyploids are sometimes found among certain species of fish and amphibians
polyploidy in animals is useful to humans as it can be induced artificially for example to produce sterile rainbow trout to stock fishing areas
polyploidy in mammals is often lethal
a rare example of a polyploidy mammal is viscacha rat which is tetraploid