Unit 1: Human Cells: Chapter 4: Mutations

Question 1

Mutation

Answer 1

A change in the structure of composition of an organisms genome. Varies from tiny change in DNA structure if a gene to large scale alteration in chromosome structure of number.

Question 2

Mutant

Answer 2

An individual affected by a mutation, when a change in genotype caused by mutation also produces a change in phenotype.

Question 3

Frequency of mutation

Answer 3

Expressed as number of mutations that occur at that gene site per million gametes.
Without influence of external factors, mutations occur spontaneously, randomly & rarely.

Question 4

Mutagenic agents

Answer 4

Include certain chemicals (mustard gas), and various types of radiation ( gamma rays, X-rays, Uv light). Resultant mutations are described as INDUCED.

Question 5

Genetic disorder

Answer 5

A condition or disease that is directly related to an individual’s genotype.

Question 6

Single gene mutation

Answer 6

Alteration of a nucleotide sequence in a gene’s DNA

• point mutation
• splice site mutation

Question 7

Point mutation

Answer 7

Type of single gene mutation involving a change in 1 nucleotide in DNA sequence of a gene. There are 3 types of point mutation.
- substitution
- insertion
- deletion
All result on 1+ codons for 1+ amino acids being altered.

Question 8

Splice site mutation

Answer 8

Alteration of splice site nucleotide sequence on parts of introns which flank exon. Mutation at splice sites may result in introns being left in or exons being left out of mature transcript of mRNA.

Question 9

Impact on protein structure: Missense

Answer 9

Change on genome caused by mutation where coding for an amino acid still makes sense but not the original sense.
See case studies on Sickle Cell disease & PKU

Question 10

Impact on protein structure: Nonsense

Answer 10

Codon that used to code for an amino acid is substituted for one that acts as a premature stop codon. Protein synthesis is halted early, resulting in formation of shorter polypeptide chain which is unable to function.

Question 11

Impact on protein structure: splice-site mutation

Answer 11

One or more introns retained in mature mRNA transcript, creating an altered protein that cannot function properly.
See case study on beta thalassaemia

Question 12

Impact on protein structure: frameshift

Answer 12

mRNA read as series of triplets ( codons) during transcription. If a base pair is inserted or deleted, the reading frame (triplet grouping) of the genetic code is shifted in a way that alters every subsequent codon & amino acid coded along the remaining length of the gene. Protein formed will almost certainly be non functional.

Question 13

Allele

Answer 13

Variations of a specific gene

Question 14

Homozygous

Answer 14

Individual is said to be homozygous for a gene if he/she receives 2 identical copies of a gene, 1 from each parent.

Question 15

Heterozygous

Answer 15

Individual is said to be heterozygous for a gene if he/she receives 2 different alleles of a gene, 1 from each parent.

Question 16

Chromosome structure mutations

Answer 16

Involve the breakage of one or more chromosomes. Broken end of chromosome is sticky & can join to another broken end.

Question 17

Chromosome structure mutations: deletion

Answer 17

Occurs when chromosome breaks in 2 places. Segment in between becomes detached, 2 broken ends join to form a shortened chromosome which lacks certain genes. Usually has drastic effect on organism concerned.

Question 18

Chromosome structure mutations: duplication

Answer 18

Segment of genes becomes attached to one end of the first chromosome or inserted somewhere along its length. Results on a set of genes being repeated.
Cancer is common cause of duplication.

Question 19

Chromosome structure mutations: translocation

Answer 19

Section of chromosome breaks off f becomes attached to different chromosome i.e. NOT it’s homologous partner. Most common type of mutation associated with cancer.
See case study on CML

Question 20

Chromosome structure mutations: inversion

Answer 20

A chromosome breaks in 2 places. The segment in between flips over before rejoining the broken chromosome again. This causes a reversal of normal gene sequence & is often fatal.
See case study on Haemophilia A