1. Using the table on Pg. 292, write the amino acid sequence that would be made according to the codons on the mRNA chain.

2. Why do you think this exact base sequence is important?

• Categorize the different kinds of mutations that can occur in DNA.

Section Objectives:

• Compare the effects of different kinds of mutations on cells and organisms.

Mutations

• Any change in DNA sequence is called a mutation.

• Mutations can be caused by errors in replication, transcription, cell division, or by external agents.

• Mutations can affect the reproductive cells of an organism by changing the sequence of nucleotides

within a gene in a sperm or an egg cell.

Mutations that can be passed on

• If this cell takes part in fertilization, the altered gene would become part of the genetic makeup of the

offspring.

• A mutation may produce a new trait or it may result in a protein that does not work correctly.

• Sometimes, the mutation results in a protein that is nonfunctional, and the embryo may not survive.

• In some rare cases a gene mutation may have positive effects.

Mutations in reproductive cells

• What happens if powerful radiation hits the DNA of a nonreproductive cell, a cell of the body such as in skin, muscle, or bone?

• If a body cell’s DNA is changed, this mutation would not be passed on to offspring.

• However, the mutation may cause problems for the individual.

Mutations in body cells

• Damage to a gene may impair the function of the cell.

• When that cell divides, the new cells also will have the same mutation.

• Some mutations of DNA in body cells affect genes that control cell division.

• This can result in the cells growing and dividing rapidly, producing cancer.

Mutations in body cells

• A point mutation is a change in a single base pair in DNA.

• A change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein.

Types of Mutations

THE DOG BIT THE CAT.

THE DOG BIT THE CAR.

Normal

Point mutation

mRNA

ProteinStop

Stop

mRNA

Protein

Replace G with A

• An example of a point mutation, is sickle-cell disease.

• Sickle-cell diseases cause the red blood cells to be deformed. The result is that they get stuck in the blood vessels, depriving tissues of oxygen, causing strokes, and blood clots.

A point mutation takes place when a single nitrogenous base (letter) is changed at one point.

Types of Mutations

THE DOG BIT THE CAT.

THE DOG BIT THE CAR.

What would happen if a single nitrogenous base (letter) is deleted?

THE DOG BIT THE CAT.

THD OGB ITT HEC AT.

• A mutation in which a single base is added or deleted from DNA is called a frameshift mutation because it shifts the reading of codons by one base.

Deletion of U

Types of Mutations

• The new sequence with the deleted base would be transcribed into mRNA.

• But then, the mRNA would be out of position by one base.

Deletion of U

• This mutation would cause nearly every amino acid in the protein after the deletion to be changed.

Types of Mutations

• Frameshift mutations can cause severe genetic diseases like Cystic Fibrosis and Lou Gehrig’s Disease.

Frameshift mutations

• Lou Gehrig’s Disease is a progressive neurological disease. Affects nerve cells used for voluntary muscle control

Lou Gehrig’s Disease, or Amyotrophic Lateral Sclerosis (ALS) is caused by a frameshift mutation on

chromosome 21.

Human Karyotype

With ALS, there is a deletion of a Cytosine on this gene.

Every other base moves down, making all the amino acids incorrect after that.

• Cystic fibrosis (CF) is one of the most common fatal genetic disorders among Americans.

• It affects the lungs and digestive tract

Cystic Fibrosis

• Due to a defective protein in the plasma membrane, cystic fibrosis results in the formation and

accumulation of thick mucus in the lungs and digestive tract.

Cystic Fibrosis is caused by a frameshift mutation on chromosome 7.

Three nitrogenous bases are deleted to cause this mutation in the amino acid sequence.

• Changes may occur in chromosomes as well as in genes.

• Sometimes during mitosis or meiosis chromosomes break and then rejoin incorrectly, or just a piece breaks off for good.

• Structural changes in chromosomes are called chromosomal mutations.

Chromosomal Alterations

• Some mutations seem to just happen, perhaps as a mistake in base pairing during DNA replication.

• These mutations are said to be spontaneous.

• However, many mutations are caused by factors in the environment, such as radiation, chemicals, and even high temperatures.

Causes of Mutations

• Any agent that can cause a change in DNA is called a mutagen.

Repairing DNA

• Enzymes proofread the DNA and replace incorrect nucleotides with correct nucleotides.

• These repair mechanisms work extremely well, but they are not perfect.

• The greater the exposure to a mutagen such as UV light, the more likely is the chance that a mistake will

not be corrected.

Any change in DNA sequences is called a _______.

Question 1

D. translation

C. transcription

B. mutation

A. replication

The answer is B.

Which is more serious, a point mutation or a frameshift mutation? Why?

Question 2

Answer

A frameshift mutation is more serious than a point mutation because it disrupts more codons than a point mutation.

Why are chromosomal mutations rarely passed on to the next generation?

Question 3

AnswerFew chromosomal changes are passed on to the next generation because the zygote usually dies. If the zygote survives, it is often sterile and incapable of producing offspring.