Key Area 6: Mutations

Question 1

Define ‘mutations’ and describe the effect of one

Answer 1

Mutations are a change in the structure or amount of an organisms DNA. Mutations arise spontaneously and at random. Mutations rates differ in different genes and different organisms

Question 2

Define single gene mutation

Answer 2

These mutations involve a change in one of the base pairs in the DNA sequence of a single gene. Also known as point mutations. These may occur in the protein-coding sequence or the regulatory sequences which control expression of the gene.

Question 3

Name 3 single gene mutations

Answer 3

Deletion, insertion, substitution

Question 4

Describe deletion single gene mutations

Answer 4

Deletion is when a base is deleted in a sequence. This changes the amino acids because of a frameshift.

Question 5

Describe insertion single gene mutations

Answer 5

Insertion is when an extra base is added to the sequence. This causes all the amino acids to change because of a frame shift

Question 6

Describe substitution single gene mutations

Answer 6

Substitution is when a nucleotide with one base has replaced a nucleotide with another base. This causes only one change of an amino acid

Question 7

Explain the difference between missense, nonsense and splice site mutations

Answer 7

Missense- these substitutions change the codon from one amino acid to another amino acid. This may result in the shape of the protein changing and not being able carry out its function. However some changes in amino acid may not have any effect
Nonsense- these substitutions change the codon from an amino acid to a stop codon. The shortened protein is generally non-functional or its function is affected
Splice-site - these substitutions affect the boundaries between exons and introns (splice sites) a mutation here can prevent splicing at that site. This will result in a very different protein being made due to the post transcriptional processing

Question 8

Define chromosome structure mutation

Answer 8

Some mutations affect the structure or number of chromosomes present in the cells of living organisms. Those affecting the structure arise when pieces of one chromosome break off and are lost or join back into the chromosome complement in a different way

Question 9

Name 4 chromosome structure mutations

Answer 9

Duplication, deletion, translocation, inversion

Question 10

Chromosome structure mutations- deletion

Answer 10

Have a drastic effect on the organism as genes are lost.

Question 11

Chromosome structure mutations- duplication

Answer 11

This results in a set of genes being repeated. Some supplications can be detrimental

Question 12

Chromosome gene mutations- inversion

Answer 12

Chromosome breaks in two places and a set of genes rotates through 180 degrees. This reverses the normal sequence of genes. This often results in the formation of non-viable gametes

Question 13

Chromosome structure mutations- translocation

Answer 13

Detached genes become attached to a different chromosome in the complement. Translocation involves transfer of genes from one chromosome to another. This results in problems pairing chromosomes during gamete formation and leads to non-variable gametes

Question 14

Explain the importance of mutation and gene duplication to evolution

Answer 14

Duplication of a gene produces a second copy of the gene which is free from selection pressure. This means it can mutate to produce new DNA sequences.this may confer advantages to the organism and possibly increase it fitness and chances of survival

Question 15

Define polyploidy

Answer 15

Polyploidy is duplication of all the chromosomes resulting in extra sets of chromosomes. It is the result of an error during gamete formation

Question 16

Polyploidy in plants

Answer 16

Polyploidy plants are normally larger and have increased seed and fruit size. This is of economic importance. Polyploidy plants with an odd number of sets of chromosomes are sterile.his allows the production of seedless fruits

Question 17

Polyploidy in animals

Answer 17

it is thought that polyploidy contributed to the evolution of vertebrate animals. Mammals which are polyploidy fail to survive except plains viscacha rat of Argentina

Question 18

Polyploidy human food crops

Answer 18

Polyploidy plants are often larger, stronger and more productive than their diploid ancestors. This has led to humans bringing these species into cultivation