MUTATIONS! Scott Hatfield Bullard Science Department Part One

MUTATIONS, PART 1: WHAT ARE THEY ?

MUTATIONS: w are changes in the genetic material of the cell.

MUTATIONS: w are changes in the genetic material of the cell. w can occur at the level of an individual DNA strand (a point mutation) or to an entire chromosome (a chromosomal mutation)

MUTATIONS: w usually lead to a decrease, rather than an increase, of information. w 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: w Point mutations are caused by random errors in the copying process (during transcription)

TYPES OF MUTATIONS: w Chromosomal mutations occur when chromosomes fail to properly separate during meiosis

Chromosomal Mutations: chromosome supercoils coils nucleosome histones DNA double helix

changes in the number or structure of chromosomes Chromosomal Mutations:

changes in the number or structure of chromosomes typically harmful in humans Chromosomal Mutations:

can occur in four different ways: deletion, duplication, inversion and translocation

Chromosomal Mutations: DELETION

Chromosomal Mutations: DELETION DUPLICATION

Chromosomal Mutations: DELETION DUPLICATION INVERSION

Chromosomal Mutations: DELETION DUPLICATION INVERSION TRANSLOCATION

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

POINT Mutations: chromosome supercoils coils nucleosome histones DNA double helix

POINT Mutations: are changes in single base pairs of DNA can lead to production of faulty (misshapen) proteins, or no protein at all

POINT Mutations: 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

POINT Mutations: that do this are called sense or silent mutations

POINT Mutations: which lead to a different amino acid, however, are called missense mutations Depending on the amino acid, these can be good, bad or neutral

POINT Mutations: which lead to a stop codon (UAA, UAG or UGA) are called nonsense mutations These lead to loss of function and are usually bad

POINT Mutations: 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 Mutations alter 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: w can occur in any cell w that occur in gametes (eggs or sperm) are called germ-line mutations since they occur during the germination of new offspring (reproduction). w 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 the loss 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 the loss 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 the loss of information leads to the loss of some critical function. Somatic Mutations:

cell division 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 are called 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 and Mutation Sunlight contains many frequencies of radiation, but most are filtered out by the atmosphere.

Ultraviolet Light and Mutation Sunlight contains many frequencies of radiation, but most are filtered out by the atmosphere. UV-B radiation does get through, however, triggering a chemical change in DNA, a point mutation

Ultraviolet Light and Mutation Sunlight contains many frequencies of radiation, but most are filtered out by the atmosphere. UV-B radiation does get through, however, triggering a chemical change in DNA, a point mutation (This can affect the health of organisms like the plants shown in the graphic)

Ultraviolet Light and Mutation UV-B radiation provides energy that drives two thymine nucleotides together.

Ultraviolet Light and Mutation UV-B radiation provides energy that drives two thymine nucleotides together. These thymine dimers pull in, effectively eliminating a single nucleotide.

Ultraviolet Light and Mutation UV-B radiation provides energy that drives two thymine nucleotides together. These thymine dimers pull in, effectively eliminating a single nucleotide. This single point mutation also destroys information, leading to loss of function.

Ultraviolet Light and Mutation Loss of function may mitosis disrupt the regular cell cycle (G 1, S 1, G 2, mitosis and cytokinesis)

Ultraviolet Light and Mutation Loss of function may disrupt the regular cell cycle (G 1, S 1, G 2, mitosis and cytokinesis) If this happens, the cell may divide more often than it should !

Ultraviolet Light and Mutation Loss of function may disrupt the regular cell cycle (G 1, S 1, G 2, mitosis and cytokinesis) If this happens, the cell may divide more often than it should ! Uncontrolled cell growth goes 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 contain many ingredients known to cause cancer and other forms of lung disease.

Don’t let mutation freak you out !

Don’t let mutation freak you out !

Don’t let mutation Freak you out !

Don’t let mutation Freak 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 us to avoid mutagens whenever 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.