key area 1.6 - mutation

Question 1

mutation

Answer 1

• a rare, random change in an organisms DNA

Question 2

single gene mutations

Answer 2

• occur within genes and involve DNA nucleotide sequence being altered as a result of substitution, insertion or deletion of nucleotides

Question 3

chromosome structure mutations

Answer 3

• an alteration on the number or sequence of genes in a chromosome as a result of duplication, deletion, inversion or translocation
• arise when pieces of one chromosome break off and are lost or join back into the chromosome complement in a different way

Question 4

substitution

Answer 4

• one nucleotide is substituted for another
• eg CATCAT => CCTCAT

Question 5

insertion

Answer 5

• one or more nucleotides are inserted in a section of DNA
  eg CATCAT => ACATCATCAT

Question 6

deletion - single gene

Answer 6

• one or more nucleotides are deleted in a section of DNA
• eg CATCAT => CTCAT

Question 7

substitution mutations - types and effect

Answer 7

• missense : a codon is altered so codes for an amino acid but not in the original sense, protein could be non functional or have little effect
• nonsense : the substation codes for a stop codon; polypeptide chain will be shorter producing either a non functional or a different protein
• splice site : mutation occurs in an area which marks start or end of an intron which could lead to introns being included in mature transcript and exons being left out, non functional protein may be produced

Question 8

effects of insertion or deletion mutations - single gene

Answer 8

• major effect on protein likely as all amino acids coded for after the mutation could be effected as all nucleotides are moved from original place
• this is known as a frame shift mutation

Question 9

duplication

Answer 9

• sets of genes from one chromosome become attacked to a homologous parter leading to repeated genes
• original gene can still be expressed but potential beneficial mutations can occur in duplicated gene
• eg ABCDEF => ABBCDEF

Question 10

deletion - chromosome structure

Answer 10

• detached genes are lost completely
• eg ABCDEF => ACDEF

Question 11

inversion

Answer 11

• chromosome breaks in two places and a set of genes rotates through 180°
• eg ABCDEF => AEDCBF

Question 12

translocation

Answer 12

• detached genes become attached to a non homologous chromosome in the compliment

Question 13

importance of mutations

Answer 13

• mutations are a new source of variation so new alleles of genes can constantly be produced