3.4.3 Genetic diversity can arise as a result of mutation or during meiosis

Content:

Gene mutations involve a change in the base sequence of chromosomes.

They can arise spontaneously during DNA replication and include base 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.

Meiosis produces daughter cells that are genetically different from each other.

The process of meiosis only in sufficient detail to show how:

two nuclear divisions result usually in the formation of four haploid daughter cells from a single diploid parent cell
genetically different daughter cells result from the independent segregation of homologous chromosomes
crossing over between homologous chromosomes results in further genetic variation among daughter cells.

Students should be able to:

complete diagrams showing the chromosome content of cells after the first and second meiotic division, when given the chromosome content of the parent cell
explain the different outcome of mitosis and meiosis
recognise where meiosis occurs when given information about an unfamiliar life cycle
explain how random fertilisation of haploid gametes further increases genetic variation within a species.

Mutations

Define ‘gene mutation’. (2)

Change in the base / nucleotide sequence of chromosomes / DNA

Resulting in the formation of new allele.

Explain how a gene mutation can have no effect on an individual. (2)

1.Because the genetic code is degenerate so amino acid sequence may not change.

Accept description of ‘degenerate’ i.e. some amino acids are coded by more than one triplet / codon.

OR Mutation is in an intron so amino acid sequence may not change.

2.Mutation changes the amino acid but has no effect on tertiary structure.

3.New allele is recessive so does not influence phenotype.

Explain how a gene mutation can have a positive effect on an individual. (2)

1.because a mutation can result in a change in polypeptide that positively changes the properties of the protein.

For ‘polypeptide’ accept ‘amino acid sequence’

2.May result in increased reproductive success or increased survival chances.

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