BIG QUESTIONS: ARE ALL MUTATIONS BAD? EXPLAIN.. CAN EVOLUTION OCCUR IN ABSENCE OF MUTATIONS?

Mutations The main characteristics of Waardenburg syndrome (WS) include: a wide bridge of the nose; pigmentary disturbances such as two different colored eyes, white forelock and eyelashes and premature graying of the hair; and some degree of cochlear deafness. Typically dominant.

Mutations Errors in the DNA sequence that are inherited. Possible negative, positive or unknown side effects. Our brain enlarged because of a series of mutations. The side effect of a mutation may not be seen immediately, since diploid (eukaryotic) organisms have two copies of each gene. Therefore, an error in one gene may be masked by the other. Werner’s Syndrome: premature aging disease that begins in adolescence or early adulthood and results in the appearance of old age by 30-40 years of age. Its physical characteristics may include short stature and other features usually developing during adulthood: wrinkled skin, baldness, cataracts, muscular atrophy and a tendency to diabetes mellitus, among others. Autosomal recessive trait. The gene for Werner disease (WRN) was mapped to chromosome 8.

Types of Mutations A) Silent Mutation (Point Mutation) A single substitution of one base. No change in the amino acid; therefore, no effect. Occur in introns / non-coding regions of DNA.

Types of Mutations B) Missense Mutation A single substitution of one base. Results in a different amino acid; therefore, different protein is made. Sickle cell anaemia can be caused this way.

Types of Mutations C) Nonsense Mutation A single substitution of one base. Forms a premature stop codon; therefore, leading to the formation of an incomplete polypeptide. Often lethal.

Types of Mutations Substitution Replaces a nitrogenous base pair with another, different one. Silent / Missense / Nonsense Insertion The addition of one or more extra nucleotides in the DNA sequence. Deletion The removal of one or more nucleotides in the DNA sequence. Insertion and Deletion are usually Point mutations, but can involve more than one nucleotide in a row. They usually cause large errors. Leads to a change/shift in the reading frame (mRNA strand).

Types of Mutations D) Frameshift Mutation Causes changes in the reading frame. Caused by an insertion or a deletion. Frameshift mutation: Changes in the reading frame usually results in different amino acids being incorporated into the polypeptide. An insertion or deletion of three nucleotides will not shift the reading frame. This will result in the addition or removal of one amino acid. The presence or absence of the amino acid will cause a change in protein conformation, but it may not have as serious an impact as would not building the appropriate protein at all.

FRAMESHIFT MUTATION: HEY MAN HOW ARE YOU BRO and HEY MAN HWA REY OUB RO (remove “O” in original HOW) or HEY MAN HOQ WAR EYO UBR O (insert “Q” at W position in original HOW) Inserting or removing equivalent of 1 base pair.

The resulting nonsense (or malformed protein) is a result of a random insertion or deletion of information (nucleotides) and our “frame”, the manner in which we interpret this information.

Types of Mutations E) Translocation The transfer of a fragment of DNA between two nonhomologous chromosomes. Large segments of DNA can move from one location on the genome to another. The translocated fragment of DNA is referred to as a “transposable element” or a “transposon”. Translocation is associated with some types of leukemia.

Types of Mutations F) Inversion The reversal of a segment of DNA within a chromosome (i.e., copied backwards). No gain or loss of genetic information. A gene may be disrupted.

Figure 1, p. 260

Causes of Genetic Mutations Spontaneous Mutations Caused by errors in DNA replication. DNA polymerase I rereads duplicated DNA for errors, but it isn’t perfect…point mutations may result (insertion / deletion / silent mutation / missence mutation / nonsense mutation)

Causes of Genetic Mutations Induced Mutations Caused by mutagenic agents. Mutagenic agents include UV radiation, cosmic rays, X-rays and certain chemicals. UV light penetrates skin cells and can cause point mutations; can cause “dimers” – a double-bond nitrogenous base, which leads to a structural disruption to DNA and interferes with replication. X-rays’ high frequency waves break phosphate backbone of DNA. Chemicals can have a similar structure to the nitrogenous bases (C, G, A, T), thus mimicking DNA and binding instead (competitively).

Nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.

Mutation of brown eyes to blue represents neither a positive nor a negative mutation. It is one of several mutations such as hair colour, baldness, freckles and beauty spots, which neither increases nor reduces a human’s chance of survival.

BIG QUESTION: How did “human like” traits such as a smaller jaw (relative to apes) and hairlessness pop up when they don’t appear in the wild in any real frequency?

Our diets changed and our brains got bigger, pressures that caused a smaller jaw. Another way to look at this – what if our diets changed and our brains got bigger due to proto-human society adapting to mutation of the jaw?