First lesson back TASK 1 – GOT THROUGH HW TRANSLATION QUESTIONS TASK 2 – REVISE TRANSCRIPTION AND TRANSLATION

Unit 4: Genetic Information, Variation and Relationships between Organisms Lesson 5 Mutations GENE MUTATIONS INVOLVE A CHANGE IN THE BASE SEQUENCE OF CHROMOSOMES. THEY CAN ARISE SPONTANEOUSLY DURING DNA REPLICATION AND INCLUDE BASE ADDITION, DELETION AND BASE SUBSTITUTION. DUE TO THE DEGENERATE NATURE OF THE GENETIC CODE, NOT ALL BASE SUBSTITUTIONS CAUSE A CHANGE IN THE SEQUENCE OF ENCODED AMINO ACIDS. MUTAGENIC AGENTS CAN INCREASE THE RATE OF GENE MUTATION. MUTATIONS IN THE NUMBER OF CHROMOSOMES CAN ARISE SPONTANEOUSLY BY CHROMOSOME NON-DISJUNCTION DURING MEIOSIS.

Mutations What is a mutation? Discuss this? Mutations invovle a change in the base sequence of a chromosome or the number of chromosomes. Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base addition, deletion and base substitution. Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. Mutagenic agents can increase the rate of gene mutation. Mutations in the number of chromosomes can arise spontaneously by chromosome non- disjunction during meiosis.

Mutations in number of chromosomes. These can occur in meiosis and mitosis when chromosomes don’t separate correctly during division and so one cell has more chromosomes than others. E.g. an extra copy of chromosome 21 when fertilised – Downs Syndrome. Cytogenetics: study of the structure and biology of chromosomes. Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base addition, deletion and base substitution. Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. Mutagenic agents can increase the rate of gene mutation. Mutations in the number of chromosomes can arise spontaneously by chromosome non- disjunction during meiosis.

Mutations in the base sequence Look around the room and find out about the types of mutations possible in base sequence – make notes on each and answer the questions Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base addition, deletion and base substitution. Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. Mutagenic agents can increase the rate of gene mutation. Mutations in the number of chromosomes can arise spontaneously by chromosome non- disjunction during meiosis. SUMMARY : In base deletions and additions, there is frame shift. The entire DNA frame is shifted and all codons from the mutation onwards are affected. This often leads to a truncated protein (cut short) or no protein at all. In base substitutions there isn’t a frame shift. The consequences of a change depends on which base in a codon as been affected. As the DNA code is degenerate (more than one codon can code for an amino acid),if the third base is changed, there may be no affect on the protein made. If the first or second base is changed, it could lead to coding for a different amino acid and so a different protein (maybe faulty, maybe just a different variant…. (alleles – variant of a gene causing a slightly different protein)

Base addition A single base or a small number of bases are inserted into the sequence of DNA when it is replicated. Original : CTA AAT CCG GCA TAG CGT Mutated version: CTA AAT TCC GGC ATA GCG T. QUESTIONS: What does this do to the reading frame of the DNA? What could be the results? Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base addition, deletion and base substitution. Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. Mutagenic agents can increase the rate of gene mutation. Mutations in the number of chromosomes can arise spontaneously by chromosome non- disjunction during meiosis.

Base deletion Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base addition, deletion and base substitution. Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. Mutagenic agents can increase the rate of gene mutation. Mutations in the number of chromosomes can arise spontaneously by chromosome non- disjunction during meiosis. A single base or a small number of bases are deleted/removed from the sequence of DNA when it is replicated. Original : CTA AAT CCG GCA TAG CGT Mutated version: CTA AAT CCG GCT AGC GT QUESTIONS: Which base has been deleted? What does this do to the reading frame of the DNA? What could be the results?

Base Substitution Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base addition, deletion and base substitution. Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. Mutagenic agents can increase the rate of gene mutation. Mutations in the number of chromosomes can arise spontaneously by chromosome non- disjunction during meiosis. A single base is changed from the original sequence of DNA when it is replicated. Original : CTA AAT CCG GCA TAG CGT Mutated version: CTA AAT CCT GCT AGC GT QUESTIONS: Which base has been changed? What does this do to the reading frame of the DNA? What could be the results? Might there be different outcomes depending of the substituted base? Explain fully