Lecture 4q Flashcards
What are the requirements of natural selection?
Variation in the trait must exist
The variation must be heritable to some degree
Differential survival and reproduction on the basis of the variable trait
What is purifying selection?
Most nonsynonymous mutations will be disadvantageous and therefore selected against resulting in there being a higher rate of synonymous than non-synonymous mutations
There will however be some non-synonymous mutations which are neutral or selected for
What is neutral evolution?
Sequences in which changes are selectively neutral for example pseudo genes, introns or codons 3rd position
Causing a steady accumulation of substitutions which can be used to infer order and timing of evolutionary divergences by calibrating the molecular clock
What is adaptive evolution?
Heritable variation must exist before selection can act upon it this is caused by mutations which occur randomly and cannot disrupt function
It is important to note that there may be more than one genetic solution to a problem and the order the mutations arise in may determine whether or not a full solution can arise
What is regulatory sequence evolution?
Changes in the ontogeny (origin and development) of an organism can have large phenotypic effects including things such as regulatory genes affecting the timing and distribution of gene expression throughout an organisms development
Small changes to regulatory genes can have large consequences
What are the origins of new genes?
Gene families of large numbers of similar genes with related functions arise from gene duplication
What are the mechanisms for gene duplication?
Polyploidy, Gene Duplication, transposition and retrotransposition
What are the fates of duplicated genes?
The gene can become inactivated to form a pseudogene (through creation of a stop codon) or it can evolve a new function or the already existing function can become split between two copies of the gene
