B8- Mutations ✅

name the 2 types of mutations

1. gene mutation- change in base sequence of DNA on chromosomes

2. chromosomes mutation- change in the number of whole chromosomes

give 2 examples of gene mutation

base deletion or substitution

what is a mutagenic agent?

give 2 examples:

A factor that increases rate of gene mutation

eg. UV light or alpha particles

Explain how a mutation can lead to the production of a non-functional protein or enzyme

1. Changes sequence of base triplets in DNA (in a gene) so changes sequence of codons on mRNA

2. So changes sequence of amino acids in the polypeptide

3. So changes position of hydrogen / ionic / disulphide bonds (between amino acids)

4. So changes protein tertiary structure (shape) of protein

5. Enzymes - active site changes shape so substrate can’t bind, enzyme-substrate complex can’t form

Explain the possible effects of a substitution mutation

1. DNA base replaced by a different base

2. changes one triplet so changes one mRNA codon

3. So one amino acid in polypeptide changes

→ Tertiary structure may change if position of hydrogen / ionic / disulphide bonds change

OR amino acid doesn’t change

→ Due to degenerate nature of genetic code (triplet could code for same amino acid)

OR if mutation is in an intron so removed during splicing

Explain the possible effects of a deletion mutation

KEY WORD = sequence

1. One nucleotide / base (pair) removed from DNA sequence

2. Changes sequence of DNA triplets from point of mutation (frameshift)

3. Changes sequence of mRNA codons after point of mutation

4. Changes sequence of amino acids in primary structure of polypeptide

5. Changes position of hydrogen / ionic / disulphide bonds in tertiary

structure of protein

Changes tertiary structure / shape of protein

describe the features of homologous chromosomes

same genes in same loci, but may have different alleles

describe the difference between diploid and haploid cells

diploid- has 2 complete sets of chromosomes, represented as 2n

haploid- a single set of unpaired chromosomes, represented as n