Download lecture 2: biological diversity in organisms

Bioinformatics
Lecture 2: Biodiversity: mutations
and inheritance
Stability and Adaptability
• Stability: cell/tissue remains in an unchanged state. Cell structure protects
it from the external environment; nuclear membrane protects the DNA….
• Adaptability: is essential to survival and creating the diversity of life that
exists occur via mutations:
• A mutation is a change, mostly permanent, to the DNA and can be
classified into 2 types chromosomal mutation and point mutations
• Diversity is determined by the cell type of the mutation
– Somatic mutation: in the non reproductive cells; not passed on next
generation
– Germ-line mutation: reproductive cells [gametes] ; may passed on to next
generation
• The Chromosome where the mutation occurs is important in determining
the effect on the physical characteristics:[ refer to supplementary material
on inheritance]
• Autosomal mutation (number 1 to 22)
• X-linked mutation X/Y chromosome
Classical (autosomal) Mendelian
Inheritance
Somatic Monohybrid cross Adapted from ref [1] p42
X-linked inheritance
• Haemophilia: (a classical case is son Alexei of last
tzar of Russia who was related to queen Victoria)
–
–
–
–
–
X chromosome has the normal/defective gene (H/h)
Y chromosome has no gene (smaller in size)
Defective allele is recessive
Male is XY and Female is XX
Homozygous defective results in the disease
• This includes a defective allele in males
– Homozygous/heterozygous normal results in no
physical effects.
Illustration of royal disease
Point Mutations
•
•
A Mutation affects only one DNA molecule
– Can , but not always, change the type of
amino acid [see later]
–
Substitution: Two types
• A /G is called a transition; T/C is called
a transversion
–
–
Insertion : causes a frameshift to the left
the resulting sentence is non sense
–
Deletion : causes a frameshift to the right:
the resulting sentence is non sense
Note In genetics the bases (letter of a DNA
molecule) are read in sets of three, where each 3
“can” have different result; just as in this example
using 3 letter words).
Mutations: Physical (Phenotypic) effects
• Mutations “can” alter the current (wild type)
protein [Phenotype] by changing the underlying
Genotype
• Physical effects (phenotype) are:
– Loss of function [can be fatal]:
• Null mutation (complete loss of function)
• Partial: can alter either dominant /recessive alleles ; so e.g.
if it effects recessive then only homozygous recessive trait is
affected
– Gain in function: mostly produces a dominant trait
– No affect: neutral mutations. Most mutations occur in
non-coding regions and are referred to as
Supplementary material
• Supplementary material of this lecture covers:
• Inheritance of “mutations” (changes to gene
sequences)
• The possible effects of the mutations on the
phenotypes (physical manifestation of the
gene(s)”
• Chromosomal mutations.
Possible Exam
• Describe the types of point mutations and
how they would affect a DNA sequence.
[would form part of a question.]
Reference
• Klug et al; Essentials of Genetics 7ed
– Chapter 6/ 14 (mutations) and Chapter 3
(inheritance)
• Klug et al: Essentials of Genetics 8ed
– Available as (e-book)
– Chapter 6/14 (mutations) and Chapter 3
(inheritance)
–