Mutations

General Definition

Long Notes:

• Any change in DNA sequence is called a mutation.

Abbreviated Notes (AN):

• Mutation (mut) = DNA sequence (seq) change

General Definition

Long Notes:

• Mutations may affect only one gene, or they may affect whole chromosomes.

(AN):

• Mut – 1 gene or whole chromosome

Types

Long Notes:

• There are three basic types of mutations:

– Point Mutation

– Frameshift Mutation

– Chromosomal Mutation

(AN):

• 3 types mut.:

– Point Mut. (PM)

– Frameshift Mut. (FM)

– Chromosomal Mut. (CM)

Point Mutations

Long Notes:

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

(AN):

• PM = change in 1 base pair in DNA

Point Mutations

Long Notes:

• 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.

(AN):

• PM = 1 amino acid (AA) change, can change protein shape

The effects of point mutations

Normal

Point mutatio

n

mRNA

Protein Stop

Stop

mRNA

Protein

Replace G with A

Frameshift

Long Notes:

• 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.

(AN):

• FM = +/- 1 base, causes shift in codons

Frameshift mutations

mRNA

ProteinFrameshif

t mutation

Deletion of U

Frameshift

Long Notes:

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

(AN):

• FM – causes most AA in protein after +/- to be wrong

Frameshift

Chromosomal Mutations

Long Notes:

• Few chromosomal mutations are passed on to the next generation because the zygote usually dies.

(AN):

• CM – zygote usually dies

Chromosomal Mutations

Long Notes:• In cases where the zygote lives and develops,

the mature organism is often sterile and thus incapable of producing offspring.

(AN):

• CM – if lives, usually sterile

Chromosomal Mutations

Long Notes:

• When a part of a chromosome is left out, a deletion occurs.

(AN):

• CM – part left out = deletion

Deletion

A B C D E F G H A B C E F G H

Chromosomal Mutations

Long Notes:

• When part of a chromatid breaks off and attaches to its sister chromatid, an insertion occurs.

• The result is a duplication of genes on the same chromosome.

(AN):• CM – gets duplicate part from sister chromatid

= insertion

Insertion

A B C D E F G H A B C B C D E F G H

Chromosomal Mutations

Long Notes:• When part of a chromosome breaks off and

reattaches backwards, an inversion occurs.

(AN):

• CM – part flipping around = inversion

Inversion

A B C D E F G H A D C B E FG H

AB E FDCBX AWC HGGE HD F

WXY Z Y ZTranslocation

Chromosomal Mutations

Long Notes:

• When part of one chromosome breaks off and is added to a different chromosome, a translocation occurs.

(AN):

• CM – part breaks off & sticks to another chromosome = translocation

General Results

Long Notes:• Mutations in eggs or sperm affect future

generations by producing offspring with new characteristics.

(AN):

• Mut. egg/sperm = pass offspring

General Results

Long Notes:• Mutations in body cells affect only the individual

and may result in cancer.

(AN):

• Mut. body cells = cancer (maybe)

Reproductive Cells

Long Notes:

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

(AN):

• maybe new trait, maybe bad protein

Reproductive Cells

Long Notes:

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

(AN):

• protein doesn’t work, embryo might die

Reproductive Cells

Reproductive Cells

Long Notes:

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

(AN):

• + effects rare

Somatic Cells

Long Notes:

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

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

(AN):

• Cell might not work right.

• Divides – new cells have mut.

Somatic Cells

NormalCell

NormalCell

MutatedCell

Mutation

NormalCell

NormalCell

MutatedCell

MutatedCell

MutatedCell

MutatedCell

MutatedCell

MutatedCell

NormalCell

NormalCell

NormalCell

NormalCell

Somatic Cells

Long Notes:

• 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.

(AN):

• Mut. might affect genes for mitosis.

• Too much growth/division = cancer.

Causes

Long Notes:

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

(AN):

• Mut. from replication, transcription, cell div. or ex. agents.

Causes

Long Notes:

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

• These mutations are said to be spontaneous.

(AN):

• Spontaneous mut. “just happen”.

Causes

Long Notes:

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

• Mutagens include radiation, chemicals, and even high temperatures.

(AN):

• Mutagen – causes mut., radiation, chems, high temps

Causes

Long Notes:

• Forms of radiation, such as X rays, cosmic rays, ultraviolet light, and nuclear radiation, are dangerous mutagens because the energy they contain can damage or break apart DNA.

(AN):

• Radiation = Xrays, cosmic rays, UV light, nuclear rad. (all high energy)

Causes

Long Notes:

• The breaking and reforming of a double-stranded DNA molecule can result in deletions.

(AN):

• Deletions from break/remake DNA

Causes

Long Notes:

• Chemical mutagens include dioxins, asbestos, benzene, and formaldehyde, substances that are commonly found in buildings and in the environment.

(AN):

• Chemicals = dioxins, asbestos, benzene, formaldehyde; in buildings & environment

Causes

Long Notes:

• Chemical mutagens usually cause substitution mutations.

(AN):

• Chems – usually substitution mut.

Repairing DNA

Long Notes:

• Repair mechanisms that fix mutations in cells have evolved.

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

(AN):

• Evolved repair to fix mut. like enzymes to proofread/ fix DNA

Repairing DNA

Long Notes:

• 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.

(AN):

• Good, not perfect.

• More mutagen, more chance of mistake.

Any change in DNA sequences is called a _______.

D. translation C. transcription B. mutation A. replication

The answer is B.

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

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?

Few 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.