DNA Mutations

Chapter 12.4

Mutation• Mutation: Any change in a gene is a

mutation.• Substances that cause a mutation are

called mutagens. • Mutations can also happen spontaneously.

Point Mutation• A change in one nucleotide

• Original: The fat cat ate the wee rat. Point Mutation: The fat hat ate the wee rat.

Point Mutation• Base Substitution - One nucleotide is

replaced with another nucleotide.

ACC CUA GGC AUC AU ACC UUA GGC AUC AU

“C” is substituted with “U”

Redundant Systems• Sometimes these mutations have no

effect!! Ex. The codons of UCU, UCC, UCA, & UCG all code for the amino acid Serine. Any substitution in the third base of the codon has no effect.

• However, a substitution in the first or the second base of the codon, changes the code for the amino acid.

• UUU codon is for phenylalanine• UCU codon is for serine• CUU codon is for leucine

Frameshift Mutations• Either the insertion or a deletion of a

nucleotide which results in a shift in the code and mistakes from the point of mutation on.

• Original The fat cat ate the wee rat.

• Frame Shift The fat caa tet hew eer at.

Somatic Cell mutations

•Mutations happen in all organisms, if it happens in a somatic cell then only the individual is affected.

Meiosis Mutations

•If it happens in a gamete then the mutation is passed on to the offspring.

Meiosis Mutations

• Mistakes during meiosis: Mistakes during meiosis, such as non-disjunction, can result in three chromosomes instead of a pair (trisomy) or more than three (polyploidy).

Down’s Syndrome• Trisomy in humans can result in birth

defects such as trisomy 21, or Down’s syndrome.

Quick Review• Point mutations

occur as a result of a change in one nucleotide.

• The 2 basic types of point mutations are base substitutions and frame shift.

Quick Review• Substitution

mutations are the result of one nucleotide being replaced by another. This results in one amino acid being incorrectly coded.

Quick Review• Frame shift

mutations are the result of either a deletion or an insertion of a nucleotide. This results in a mistake in all the triplet codes from the mutation on.

Gene Mutations• Gene Mutations occur as a result of

changes in chromosomal fragments. There are four basic types:

• 1. Translocation• 2. Inversion• 3. Insertion• 4. Deletion

Gene Mutations1.Translocation

s - When part of one chromosome breaks off and is added to a different chromosome.

Gene Mutations2. Inversion –

When part of a chromosome breaks out and is reinserted backwards.

Gene Mutations

3. Insertion When part of a chromatid breaks off and attaches to its sister chromatid. The result is a duplication of genes on the same chromosome.

Gene Mutations

4. Deletion

When part of a chromosome is left out.

Mutations & Evolution

• Mutations that have a negative effect usually result in the loss of that mutation due to the law of the survival of the fittest.

Mutation & Evolution• However, there are

times that the mutations are beneficial and result in the evolution of the species and increased variation in the population.

• We’ll learn much more about this next unit!!!