Lecture AP Biology Chapter 21 Genomes and their evolution

This chapter explain how linkage mapping, physical mapping, and DNA sequencing each contributed to the Human Genome Project, define the fields of proteomics and genomics, describe the surprising findings of the Human Genome Project with respect to the size of the human genome, distinguish between transposons and retrotransposons.

Genomes and Their Evolution

 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 Repetitive

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

Moves within genome via DNA intermediate

“cut & paste” or “copy & paste” mechanisms

Requires enzyme transposasetransposase

 Move by means of RNA intermediate

 Leaves copy at original site

 Involves enzyme reverse transcriptasereverse 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: -globin and globin and -globin and 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, Antifreeze proteins (AFP):

plants, fungi, bacteria to aid survival in sub-globin and zero

environments

 Function: bind to ice crystals and prevent growth

 Antarctic fish: old protein gene transformed into a new Antarctic fish

gene with new structure/function

 Gene mutates  duplicated  divergent evolution

Evolutionary Development

(Evo-globin and devo)

understand how changes can lead to evolution of organisms

Homeotic genes

Homeotic genes: master regulatory genes

of body parts

Homeobox

Homeobox: widely conserved 180-nucleotide sequence within homeotic (Hox) genes

plants)

Conservation of homeotic genes