Lecture 17 - Genomes and their Evolution

BIOLO

Genomics

Field of study where scientists analyze and study whole sets of genes and their interactions

Bioinformatics

The application of computation methods to the storage and analysis of biological data

Human Genome Project

Sequencing the entire genome of humans, established databases

Proteomics

Study of the relationship and structures of proteins and their properties

Proteome

Entire set of proteins expressed by a cell or group of cells

Systems Biology

Compiling catalogs of genes and proteins and focus on their functional integration into biological systems

21,000 genes

How many genes are found within a human cell?

Alternative Splicing

Vertebrate genomes use extensive _____ of RNA transcripts… this generates more than one functional protein from a single gene. Some genes expressed in hundreds of ____ forms.

Gene Density

Number of genes present in a given length of DNA

Eukaryotes have larger genomes but lower gene density than prokaryotes

Comparison of gene density in eukaryotes vs prokaryotes

Most eukaryotic DNA does not code for protein and is NOT transcribed into functional RNAs

Some DNA in multicellular eukaryotes is present as introns within genes… introns account for most of the difference in average length between human genes (27,000 base pairs) and bacterial genes (1,000 base pairs)

Intergenic DNA

DNA sequences that don’t code for proteins or produce known RNAs… noncoding DNA. makes up the bulk of eukaryotic genome

Repetitive DNA

Most intergenic DNA is ______, which are sequences present in multiple copies in the genome

Transposable Elements

Stretches of DNA that can move from one location to another within the genome. Found in both eukaryotes and prokaryotes. Can provide sites for crossover between nonsister chromatids.

44% of entire human genome

Repetitive DNA is ______ entire human genome, and is made up of units called transposable elements and sequences related to them.

Transposition

Transposable element moves from one site in a cell’s DNA to another by a recombination process… never detach from DNA… original and new DNA sites are brought together by enzymes that bend DNA

Transposons

Type of transposable element… move by means of DNA intermediates and require a “transposase” enzyme

Retrotransposons

Type of transposable element… move by means of RNA intermediate and use enzyme “reverse transcriptase”

15% of human genome

Repetitive DNA that is not related to transposable elements (usually arise by mistakes during DNA replication and recombination). This DNA accounts for ____ of human genome. S

Simple Sequence DNA

Type of DNA that contains many copies of tandemly repeated short sequences… can be as many as 500 or as few as 15 nucleotides

Short Tandem Repeat (STR)

Repeated units contain 2-5 nucleotides… number of copies of the repeated unit can vary from site to site within a given genome

Scientists compare chromosomal organization of different species to make inferences about the evolutionary processes shaping chromosomes and driving speciation

Evolutionary Notes

Non-disjunction

Accidents in meiosis… can lead to one or more extra sets of chromosomes, a condition known as polyploidy

Alterations in Chromosomal Structure

 Comparative analyses between chromosomes of humans and six other mammals reveal the following:

 Evidence of many duplications and inversions of large portions of chromosomes.

 The rate of these events seems to have accelerated about 100 million years ago, as large dinosaurs became extinct and the number of mammalian species increased rapidly.

Slippage

____ can occur during DNA replication so that part of the template is skipped or replicated twice

Unequal crossing over during prophase I of meiosis can result in one chromosome with a deletion and another with a duplication of a particular region

Due to chromosome rearrangements, the two populations could not successfully mate with each other, a step on their way to becoming two separate species.

Transposable elements have shaped genomes over evolutionary time

Persistence of transposable elements as a large percentage of eukaryotic genome suggests that they play an important role in shaping a genome over evolutionary time.

By promoting recombination, disrupting cellular genes or control elements, and carrying entire genes or individual exons to new locations.

How have transposable elements contributed to the evolution of the genome?

It must happen in a cell that will form a gamete

For change to be heritable…

1. if element moves into middle of a coding sequence for a protein-coding gene, may prevent normal functioning of the gene

2. My insert within a regulatory sequence, thus increasing or decreasing protein production

Consequences of movement of transposable elements