MUTATIONS! Part One

MUTATIONS: WHAT ARE THEY ?

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)

w 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. MUTATIONS:

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 Chromosomal Mutations:

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…