3.4.3 Mutation and Meiosis

Define variation

Differences within or between species

Define interspecific

Mutation between species

Define intraspecific

Mutation within a species

What are the 3 main causes of variation

Mutations, meiosis, random fertilisation

Define mutation

Any change to the nucleotide sequence in DNA

Where do mutations occur

In introns

Why do mutations occur

Due to the degenerative nature of the genetic code

Define silent mutations

Mutations which do not effect the amino acid sequence

What nature do mutations occur

Randomly and spontaneously

Define mutagens

Things that increase rate of mutation

Give some examples of mutagens

Ionising radiation, environmental chemicals and HPV/viruses

Name the point mutations

Addition, deletion and substitution

Describe a deletion mutation

Removal of one base sequence

Describe a substitution mutation

Switching on base sequence for another

What does meiosis form

4 non-genetically identical daughter cells

What is the name of the meiosis product

Haploid gametes

What two ways can meiosis produce variation

Independent assortment/segregation, crossing over

Describe independent assortment/segregation

Chromosomes line uptown the equator of cells in homologous pairs - but could be in a different order

Define homologous pairs

Chromosomes with the same gene in the same loci but could have different alleles

Describe variation by crossing over

Homologous pairs of chromosomes form a bivalent at the chiasmata, equal amounts of DNA are swapped between chromosomes

Describe the chiasmata

the cross over point of two chromosomes

Define non-disjunction

A chromosome mutation which results in gametes having too many or too few chromosomes

Why do most mutations not effect the polypeptide

Because the code is degenerate

Define mutagenic agent

A factor increasing rate of mutation

Apart from mutation explain one other way genetic variation is increased (2)

Random fertilisation, produces new maternal/paternal combinations

Define gene mutation (2)

A change in base codes for amino acids, resulting in a new allele

Describe how a gene mutation may have no effect on an individual (2)

Genetic code is degenerate so may not affect tertiary structure, only amino acids

Describe crossing over and how it increases genetic diversity (4)

Homologous chromosomes form a bivalent, at the chiasma, equivalent gene sections are swapped, new combination of alleles formed

Why will all cells in a body have non-dysjunction (2)

Mutation occurs in gametes, all cells derived via mitosis