Genetics Lecture No. 6: Mutations & Mutants
Monday January 28 , 2013
Mutations & Mutants:
-A mutation is a change in DNA sequence that can be inherited. Most mutations have no effect or cause
neutral changes to the organism. Very few mutations are beneficial and some can be lethal or
problematic (mutations depend on the conditions you use to observe). A mutant is an organism that
experiences a change in its genetic sequence. The wild type is usually considered to be the norm, most
frequent and the allele that arose first. Mutants typically display a negative effect on the wild type.
Phenotypes & Mutations:
-Phnotypes are important in tracking and observing mutations in an organism. Examples of phenotypes
include altered appearance, altered growth conditions, altered behaviour, and altered molecules.
Types Of Mutations (Small Changes):
-Mutations can result from small changes (based on nucleotides) and if you alter the base on strand, you
always end up altering the base on the complementary strand. Base-pair substitutions are a type of
small change mutation that involves substituting one nucleotide for another. Transition mutations are
base-pair substitutions where the same type of nucleotide is exchanged (two types: purine–purine and
pyrimidine–pyrimidine) and transversion mutations are base-pair substitutions where one type of
nucleotide is exchanged for another (four types: G–C => T–A, G–C => C–G, A–T => C–G, A–T => T–A).
Insertion mutations and deletion mutations involve the addition and removal of base-pairs respectively.
Inversions are mutations that involve the double-stranded flipping of base-pairs, while translocations are
mutations that involve the movement of base-pairs along the double-helix.
Types Of Mutations (Large Changes):
-Mutations can also result from large changes (affecting chromosomes or parts of chromosomes) that
are collectively referred to as chromosome rearrangements. Chromosome duplication (two copies),
deletion (shorter), insertion (longer), inversion (flipped), and translocation (moved) are all possible
rearrangements for a single chromosome. Translocation (from one to another) and reciprocal
translocation (exchange of genetic material) are rearrangements that happen between two or more
chromosomes. Genome duplication is a rearrangement that involves all chromosomes and is not
necessarily lethal since plants do this frequently and survive.
Spontaneous Mutations & Inversed Mutations:
-Spontaneous mutations are random genetic changes that an organism is exposed to throughout the
course of its lifetime and can occur all the time. The concept that spontaneous mutations are random
was verified by bacterial resistance failing to be a response to penicillin (acted as the environmental
stimulus). In this experiment the results of the fluctuation test showed different amounts of E. Coli present in test tubes, suggesting that each bacterium had inherent spontaneous mutations for pen