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) –