Lesson Overview Mutations - Enfield High Schoolenfieldhigh.sharpschool.com/UserFiles/Servers...13.3...

Lesson OverviewLesson Overview MutationsMutations

Lesson OverviewLesson Overview13.3 Mutations13.3 Mutations13.3 Mutations13.3 Mutations

Types of Mutations

Now and then cells make mistakes in copying their own DNA, inserting the wrong base or even skipping a base as a strand is put together.

Types of Mutations

Now and then cells make mistakes in copying their own DNA, inserting the wrong base or even skipping a base as a strand is put together.

Mutations are heritable changes in genetic information. Mutations are heritable changes in genetic information.

The word mutation comes from the Latin word mutare, which means “to change.”

Types of Mutations

All mutations fall into two basic categories:

Types of Mutations

� Those that produce changes in a single gene are known as gene mutations.

Types of Mutations

� Those that produce changes in a single gene are known as gene mutations.

� Those that produce changes in whole chromosomes are known as chromosomal mutations.

Types of Mutations

Mutations that involve changes in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence.

If a gene in one cell is altered, the alteration can be passed on If a gene in one cell is altered, the alteration can be passed on to every cell that develops from the original one.

Types of Mutations

Point mutations include substitutions, insertions, and deletions.

Types of Mutations

� In a substitution, one base is changed to a different base.

Types of Mutations

� In a substitution, one base is changed to a different base.

� Substitutions usually affect no more than a single amino acid, and sometimes they have no effect at all. acid, and sometimes they have no effect at all.

Types of Mutations

In this example, the base cytosine is replaced by the base thymine, resulting in a change in the mRNA codon from CGU (arginine) to CAU (histidine).

However, a change in the last base of the codon, from CGU to However, a change in the last base of the codon, from CGU to CGA for example, would still specify the amino acid arginine.

Types of Mutations

� Insertions and deletions are point mutations in which one base is inserted or removed from the DNA sequence.

If a nucleotide is added or deleted, the bases are still read in If a nucleotide is added or deleted, the bases are still read in groups of three, but now those groupings shift in every codon that follows the mutation.

Types of Mutations

� Insertions and deletions are also called frameshiftmutations because they shift the reading frame of the genetic message.

Types of Mutations

� Frameshift mutations can change every amino acid that follows the point of the mutation and can alter a protein so much that it is unable to perform its normal functions.

Types of Mutations

Chromosomal mutations involve changes in the number or structure of chromosomes.

Types of Mutations

Chromosomal mutations involve changes in the number or structure of chromosomes.

� These mutations can change the location of genes on chromosomes and can even change the number of chromosomes and can even change the number of copies of some genes.

Types of Mutations

There are four types of chromosomal mutations: deletion, duplication, inversion, and translocation.

Types of Mutations

� Deletion involves the loss of all or part of a chromosome.

Types of Mutations

� Duplication produces an extra copy of all or part of a chromosome.

Types of Mutations

� Inversion reverses the direction of parts of a chromosome.

Types of Mutations

� Translocation occurs when part of one chromosome breaks off and attaches to another.

Effects of Mutations

Genetic material can be altered by natural events or by artificial means.

The resulting mutations may or may not affect an organism.

Some mutations that affect individual organisms can also affect a species or even an entire ecosystem.

Many mutations are produced by errors in genetic processes.

� For example, some point mutations are caused by errors during DNA replication.

The cellular machinery that replicates DNA inserts an incorrect base roughly once in every 10 million bases.

Small changes in genes can gradually accumulate over time.

Some mutations arise from mutagens, chemical or physical agents in the environment.

Chemical mutagens include certain pesticides, a few natural plant alkaloids, tobacco smoke, and environmental plant alkaloids, tobacco smoke, and environmental pollutants.

Physical mutagens include some forms of electromagnetic radiation, such as X-rays and ultraviolet light.

The effects of mutations on genes vary widely.

Some have little or no effect

Some produce beneficial variationsSome produce beneficial variations

Some negatively disrupt gene function.

� Whether a mutation is negative or beneficial depends on how its DNA changes relative to the organism’s situation.

Mutations are often thought of as negative because they Mutations are often thought of as negative because they disrupt the normal function of genes.

However, without mutations, organisms cannot evolve, because mutations are the source of genetic variability in a species.

Some of the most harmful mutations are those that dramatically change protein structure or gene activity.

� The defective proteins produced by these mutations can disrupt normal biological activities, and result in genetic disrupt normal biological activities, and result in genetic disorders.

Some cancers, for example, are the product of mutations that cause the uncontrolled growth of cells.

Some of the variation produced by mutations can be highly advantageous to an organism or species.

� Mutations often produce proteins with new or altered functions that can be useful to organisms in different or functions that can be useful to organisms in different or changing environments.

For example, mutations have helped many insects resist chemical pesticides.

Some mutations have enabled microorganisms to adapt to new chemicals in the environment.

Plant and animal breeders often make use mutations.

For example, when a complete set of chromosomes fails to separate during meiosis, the gametes that result may produce triploid (3N) or tetraploid (4N) organisms. produce triploid (3N) or tetraploid (4N) organisms.

The condition in which an organism has extra sets of chromosomes is called polyploidy.

Polyploid plants are often larger and stronger than diploid plants.

Lesson Overview Mutations - Enfield High Schoolenfieldhigh.sharpschool.com/UserFiles/Servers...13.3...

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