MUTATIONS

SC STANDARD B-4.9: The student will exemplify ways in which new characteristics are

introduced into an organism or a population

Cornell Notes

Page 110Topic: MutationsEssential Question: What is a

mutation, how do mutations allow a species to change over time?

Mutation: The Basis of Genetic ChangeA mutation is a change in the structure or

amount of genetic material of an organism

In general, genetic differences among organisms originated as some kind of genetic mutation.

Causes of Mutations

Occur naturally as accidental changes in DNA or chromosomesrepair enzymes “overlook” errors

Rate of mutation can be accelerated by some environmental factors called mutagensforms of radiationchemicals

Effects of Mutations

Depends on where and when mutations occurGerm Cell mutations

passed on to offspring

Somatic Cell Mutationsnot passed on to offspringcould result in

• Normal tissue• Cancer

Kind of Mutations

1. Mutations as changes in DNA1. Point Mutation

1. change of a single nucleotide from 1 base to another

2. Insertion or Deletion1. single nucleotide in a sequence added or dropped

1. rare

Point Mutation

Insertion or Deletion

Mutations as Changes in Results of Genes

1. Silent Mutations1. has no effect on gene’s function

2. frequently happens because genetic code is redundant

Mutations as Changes in Results of Genes

2. Missense or Replacement Mutations

codon changed so results in a different amino acid

Mutations as Changes in Results of Genes

3. Frameshift Mutations

“reading frame” of a codon depends on the starting point

insertions or deletions may shift the reading frame which may cause the remaining sequence of nucleotides to be “read” as different codons

Frameshift Mutations

Mutations as Changes in Results of Genes

4. Nonsense Mutation

results when a codon is changed from an amino acid to a “stop” signal

- resulting protein will be cut short & may fail to function

Nonsense Mutation

Mutations

5. More or Fewer Amino Acids

if an insertion or deletion is a multiple of 3 the resulting protein will have fewer or more amino acids

the more codons that are inserted or deleted the more likely the resulting protein will be malfunctioning

Chromosomal Mutations

In eukaryotic cells, the process of meiosis creates the chance of mutations at the chromosomal level: involve changing the location of genes on

chromosomes, or the numbers of copies of some genes

4 Types of Chromosomal Mutations1. Deletions

Involve loss of all or a part of a chromosome

2. DuplicationsProduce extra

copies of parts of a chromosome

3. InversionsReverse the

direction of parts of chromosomes

4. TranslocationsOccur when a

part of one chromosome breaks off & reattaches on the end of another chromosome

Trisomies

3 copies of a chromosome, in whole or in part

seen in several different chromosomes

most commonly in chromosome 21

Karyotype of Trisomy 21

Significance of Mutations

1. Neutral1. most mutations

2. Lethal or Harmful1. resulting proteins

defective, disrupt normal activity

3. Beneficial1. new altered

protein offers individual advantages

Somatic cell mutations: affect individual only

Germ Cell mutations passed on to offspringBasis for new

genetic variation in population

Polyploidy

condition in which organism has extra sets of chromosomes (due to failure in meiosis)Polyploidy plants often hardier,

larger than diploid plants

Animations

http://highered.mheducation.com/sites/0072556781/student_view0/chapter11/animation

http://www.dnatube.com/video/685/DNA--Duplication-and-Mutations