Lecture AP Biology Chapter 21 Genomes and their evolution

Genomes and Their Evolution


Bioinformatics
 Use of computers, software, and math models to

process and integrate data from sequencing projects


Human Genome Project
 Purpose: to sequence the entire human

genome
 Completed in 2003
 Genomes sequenced thus far*: 58,000
prokaryotes, 2700 eukaryotes, 5300 viruses

* Data as of 1/27/16




Human DNA
• 3 billion base pairs
• ~20,000 genes
• Only 1.5% codes for

proteins (or RNA)
• Mostly Repetitive DNA:
DNA
sequences present in

multiple copies



Transposable Elements
 Make up 75% of repetitive DNA
 Stretches of DNA that can be moved from one

location to another in genome
 Discovered by Barbara McClintock – corn
breeding experiments
 2 Types:
 Transposons
 Retrotransposons


Transposons
 Moves within genome via DNA intermediate
 “cut & paste” or “copy & paste” mechanisms
 Requires enzyme transposase


Retrotransposons
 Move by means of RNA intermediate
 Leaves copy at original site
 Involves enzyme reverse transcriptase


Genome Evolution
 Insertion effects of transposons:

 Can interrupt or alter gene function
 Multiple copies of genes
 Duplication  genes with related functions
 Genes diverge by accumulating mutations
 Some become nonfunctional pseudogenes
 Eventually, new genes with new functions can

occur


Multigene Families
 Collections of 2 or more identical or very

similar genes
 Eg. hemoglobin: α-globin and β-globin gene
families



Transposable elements contribute to
evolution
 Promote recombination, disrupt genes or

control elements, & carry genes to new
locations
 May be harmful or lethal, but can also have
small beneficial effects
 Provides raw material for natural selection

Illustrative Example: Antifreeze Gene in Fish
 Antifreeze proteins (AFP): produced by vertebrates,

plants, fungi, bacteria to aid survival in sub-zero
environments
 Function: bind to ice crystals and prevent growth
 Antarctic fish:
fish old protein gene transformed into a new
gene with new structure/function
 Gene mutates  duplicated  divergent evolution


Evolutionary Development
(Evo-devo)
• Compares developmental processes to understand

how changes can lead to evolution of organisms


Homeotic genes:
genes master regulatory genes
• Control placement and spatial organization

of body parts

Homeobox:
Homeobox widely conserved 180-nucleotide
sequence within homeotic (Hox) genes
• Found in many groups (fungi, animals,

plants)
• Hints at relatedness between all life forms


Conservation of
homeotic genes