mutations! scott hatfield bullard science department part one

MUTATIONS!Scott Hatfield

Bullard Science Department

Part One

MUTATIONS, PART 1: WHAT ARE THEY ?

MUTATIONS:

are changes in the genetic material of the cell.

MUTATIONS:

are changes in the genetic material of the cell.

can occur at the level of an individual DNA strand (a point mutation) or to an entire chromosome (a chromosomal mutation)

MUTATIONS:

usually lead to a decrease, rather than an increase, of information.

A loss of information in the cell leads to a loss of some function.

Information is lost….

The loss of information means that most mutations are either

harmful or have no effect.

.

Now and then a mutation will offer a benefit to an organism.

.

However, the idea that a single mutation would lead

to a huge, dramatic change in a single generation

(like the X-Men characters) is just wrong.

TYPES OF MUTATIONS: Point mutations are caused by random

errors in the copying process (during transcription)

TYPES OF MUTATIONS: Chromosomal mutations occur when

chromosomes fail to properly separate during meiosis

ChromosomalMutations:

chromosome

supercoils

coils

nucleosome

histones

DNAdoublehelix

• changes in the number or structure of chromosomes


• changes in the number or structure of chromosomes

• typically harmful in humans


ChromosomalMutations:• can occur in four different ways: deletion, duplication, inversion

and translocation


DELETION


DELETION

DUPLICATION


DELETION

DUPLICATION

INVERSION


DELETION

DUPLICATION

INVERSION

TRANSLOCATION

Non-Disjunction:• is the failure of the chromosomes to properly separate during meiosis

homologous chromosomesfail to separate

Meiosis I: non-disjunction

Meiosis II:

• leads to organisms with the wrong number of chromosomes

• causes birth defects like Down’s Syndrome (trisomy-21)

Non-Disjunction:

POINTMutations:

chromosome

supercoils

coils

nucleosome

histones

DNAdoublehelix

POINTMutations:

• are changes in single base pairs of DNA

• can lead to production of faulty (misshapen) proteins, or no protein at all

POINTMutations:

• often have no effect: UCC codes for serine, for example, but so does UCU, UCA or UCG

• that change the last letter in a DNA triplet may lead to the same amino acid

POINTMutations:

• that do this are called sense or silent mutations

POINTMutations:

• which lead to a different amino acid, however, are called missense mutations

• Depending on the amino acid, these can be good, bad or neutral

POINTMutations:

• which lead to a stop codon (UAA, UAG or UGA) are called nonsense mutations

• These lead to loss of function and are usually bad

POINTMutations:

• Sense, missense and nonsense mutations are typically caused by substitution of one nucleotide for another, changing the meaning of only one codon. • Deletion or insertion of an entire nucleotide leads to frameshift !

Frameshift Mutationsalter everything that follows:

THE DOG ATE THE RAT MAN

THE HOG ATE THE RAT MAN

THE DOG ATE HER ATM AN…

THE OGA TEH ERA TMA N…

MUTATIONS!Scott Hatfield

Bullard Science Department

Part Two

MUTATIONS, PART 2:Where Do They Happen ?

??

? ?

MUTATIONS: can occur in any cell

that occur in gametes (eggs or sperm) are called germ-line mutations since they occur during the germination of new offspring (reproduction).

that occur in cells other than gametes are called somatic mutations

Somatic Mutations:

Many are harmless: freckles, for example,are often the result of such mutations.

(Three flies are shown above. Two are mutants. Would these be harmless mutations, or not?)

Some are dangerous, because theloss of information leads to the loss of some critical function.

This fruit fly was born without functional eyes, but it has a white ‘eye spot’ clearly visible on its abdomen. Flying blindly is not a favored trait !

Somatic Mutations:

Some are dangerous, because theloss of information leads to the loss of some critical function.

Somatic Mutations:

Some are very dangerous, because their loss triggers runaway cell division, also known as . . .

Somatic Mutations:

Cancer!

This is a picture of skin cancer on a person’s cheek, a somatic mutation, probably triggered by UV radiation

How does this happen?

Substances which tend to cause mutations arecalled mutagens. . .

High frequencies of ultraviolet light, for example,can cause point mutations which lead to skin cancer. Let’s see how this can happen . . .

Ultraviolet Light andMutation

Sunlight contains many frequencies of radiation, butmost are filtered out by theatmosphere.



UV-B radiation does getthrough, however, triggeringa chemical change in DNA,a point mutation



UV-B radiation does getthrough, however, triggeringa chemical change in DNA,a point mutation

(This can affect the healthof organisms like the plantsshown in the graphic)


UV-B radiation provides energy that drives two thymine nucleotides together.



These thymine dimers pull in, effectively eliminating a single nucleotide.



These thymine dimers pull in, effectively eliminating a single nucleotide.

This single point mutation also destroys information, leading to loss of function.


Loss of function maydisrupt the regular cell cycle (G1, S1, G2, mitosis and cytokinesis)



If this happens, the cell may divide more often than it should !



If this happens, the cell may divide more often than it should !

Uncontrolled cell growthgoes by many names, but the generic term is cancer.

When these mutations lead to cancer, they are classified as carcinogens.

When mutations lead to cancer, they are classified as carcinogens.

Tobacco products containmany ingredients knownto cause cancer and otherforms of lung disease.

Don’t let mutationfreak you out !

Don’t let mutationFreak you out !

It’s normal for humans

to have a certain number

of somatic mutations

during their life.

It’s also healthy for all of usto avoid mutagenswhenever possible!

It’s normal for humans

to have a certain number

of somatic mutations

during their life.

We should avoid mutagens because most mutations are highly unlikely to offer benefits, but (interestingly enough) scientists have found the study of mutations very helpful!

ALLELES:

• are different versions of the same gene

• come in pairs (one from each parent)

ALLELES:

• can be either dominant (always expressed) or recessive (hidden, and only

expressed when there are no dominant alleles present)

ALLELES:

• whatever you have, whether dominant or recessive, make up the organism’s genotype

• the traits that are actually shown are the phenotype

ALLELES:

• different combinations lead to different genotypes which may still have the same phenotype

ALLELES:

• As an example, a fly with two dominant alleles and a fly with one dominant allele and one recessive allele will both have the same phenotype !

ALLELES:

• another complication is that not all alleles are expressed all the time, in every part of the organism’s body. Their expression may be hidden.

In figuring these things out, scientists have found mutations helpful, because the errors in development reveal the locus (actual physical location) of the normal allele. So research on organisms like fruit flies often involves deliberately using mutagens to cause mutations that reveal the normal allele and, eventually, that allele’s function.

mutations! scott hatfield bullard science department part one

Documents

deletion slide

meiosis slide

bad slide

transcription slide

neutral slide

chromosomal mutation

types of mutations

nonsense mutations