Biology

Chapter 12.4

What is a mutation?A change (mistake) in the

replication of genetic material.

The daughter cell is different from the parent

Gene Mutation

Most replication errors are corrected by the cell’s built in spell check system.

However, some do escape detection

Gene Mutation

Deletion – Leaving out one nucleotide in the sequence, shifts the reading of the sequence to the left, creating a totally different set of amino acids

DELETION

Normal mRNA reads:AUG AAG UUU GGC GCA UUG UAAMet Lys Phe Gly Ala Leu Stop.Mutated mRNA reads:AUG AAG UUG GCG CAU UGU AA…Met Lys Leu Ala His Cys …

Gene Mutation

Insertion – Mutation in which an extra nucleotide is added to the chain during replication, shifts reading to the right, creating a totally different set of amino acids

INSERTION

Normal mRNA reads:AUG AAG UUU GGC GCA UUG UAAMet Lys Phe Gly Ala Leu Stop.Mutated mRNA reads:AUG AAG UUU GUG CGC AUU GUA

AMet Lys Phe Val Arg Ile Val

Gene Mutation

Point Mutation – A base substitution occurs. One nucleotide is replaced with a different one

POINT MUTATION

Normal mRNA reads:AUG AAG UUU GGC GCA UUG UAAMet Lys Phe Gly Ala Leu Stop.Mutated mRNA reads:AUG AAG UUU AGC GCA UUG UAAMet Lys Phe Ser Ala Leu Stop.

Gene Mutation

These mutations arise spontaneously during DNA replication.

External agents may cause mutations, called mutagens.

Chromosome Mutations

Changes may occur in chromosomes as well as in genes.

Chromosome mutations can have serious effects on the distribution of genes to gametes during meiosis.

Chromosome Mutations

Deletion:ABCDE---FGHABCE---FGH

Chromosome Mutations

Duplication:ABCDE---FGHABCBCDE---FGH

Chromosome Mutations

Inversion:ABCDE---FGHADCBE---FGH

Chromosome Mutations

Attachment to a different chromosome:

ABCDE---FGHWXY---ZWXABCDE---FGHY---Z

Other causes of genetic variation

During meiosis, homologous pairs fail to separate.

This would cause the offspring to have an extra chromosome.

During meiosis, part of one chromatid breaks of and joins to the other (see pg 264.)

CANCER

Abnormal cells, go through cell cycle very fast, creating new cells like it.

They reproduce in an uncontrolled way, crowding out healthy cells and destroying tissues and possibly organs.

It can spread to other parts of the body

Causes of Cancer

Genes that control the cell cycle mutate, called an oncogene.

Mutations may be inherited or caused by a carcinogen, a cancer causing agent in the environment.

Tobacco smoke, radiation and other chemicals.

Causes of Cancer

Viruses may also cause cancer.Their presence disrupts normal

cell processes.They can also carry oncogenes

into the host cell.

Technology

Scientists can transfer a gene artificially from a donor organism to a bacteria.

The DNA of the bacterium is called recombinant DNA.

The bacteria will transcribe and translate the foreign gene and produce the protein it is coding for.

Technology

Small, circular pieces of DNA, called plasmids, are where the foreign DNA is placed.

Technology

To obtain a foreign gene, mRNA from a cell is isolated and DNA is produced (called reverse transcription). This single stranded DNA is converted to a double strand and this double strand is the desired gene.

Technology

In use today – goats that produce a human blood clot dissolving factor.

Plants that are disease resistant.Plants that are larger than

normal.