Eukaryotic Genomes

Demonstrate Sequence

Organization Characterized by Repetitive DNA

Honors Genetics

Lemon Bay High School

2013-2014

The Eukaryotic Genome

• prokaryotic and eukaryotic genomes encode many of the same functions

• eukaryotes encode additional functions associated with organelles• genomes of multicellular eukaryotes

encode additional functions• each eukaryotic kingdom encodes

specialized products

The Eukaryotic Genome

•Genomics

• analyzes and compares entire genomes of different organisms

• sequences of many genomes are complete

• Proteomics

• analyzes and compares the functions of the proteins in an cells, tissues, organs, organisms

The Eukaryotic GenomeRepetitive Sequences

• Genomes contain• Single copies of unique DNA sequences that make

up genes.

• Various levels of Repetitive sequences

• The majority of repetitive sequences DO NOT encode proteins.

• Three main types of repetitive sequences• Heterochromatin, Centromeres, and Telomeres

• Tandem repeats

• Transposable sequences

The Eukaryotic GenomeHighly Repetitive

Sequences• Highly repetitive sequences (103 - 106 each)

• Characteristic of short sequences repeated a large number of times.

• Found flanking the centromeres in heterochromatic regions

• Makes up a variable portion of total DNA dependent on species.• Prokaryotes do not contain satellite DNA

• Repetitive sequences re-anneal more rapidly and can be used for a variety of molecular techniques.• In situ hybridization

• Polymerase chain reaction

The Eukaryotic GenomeCentromeric DNA

Sequences• Separation of chromosomes during mitosis and meiosis depends on separation of centromeres.

• It is believed that DNA within the centromeric region is CRITICAL to this function.

• The DNA of this region binds to the kinetochore which binds to the spindle fiber during cell division.

• Proper binding of this structure is what allows the chromosome to be pulled apart during anaphase.

• Alphoid region of the centromere is a tandemarray of about 1 million base pairs that produceinstructions for the production of the kinetochore.

The Eukaryotic GenomeTelomeric DNA Sequences

• Telomeres are the “caps” of repetitive sequences that maintain the stability of chromosomes.• May be as many as 100 base pair

repeats in some organisms.• Loss of telomere sequences as we

age can result in interference with coding sequence interruption once the telomeres have been exhausted.

The Eukaryotic GenomeMiddle Repetitive

Sequences• Mini-satellites

• Variable Number Tandem Repeats (VNTRs)

• 15 to 100 bp long

• Found within and between genes

• Multiple Copy Genes

• Present when a large amount of gene product is required.

• Generally produces RNA sequences for protein synthesis

• Micro-satellites

• Short Tandem Repeats

• 5 to 50 bp long

• Useful molecular markers.

The Eukaryotic GenomeRepetitive Transposed

Sequences• Transposable elements (transposons)

• Can be mobile and move to different locations within the genome.

• Large portion of the human genome is transposable.

• SINEs

• Short Interspersed Elements

• About 500 bp long

• LINEs

• Long Interspersed Elements

• About 6000 bp long; some are expressed

• AKA retrotransposons: Protein produced is used by retroviruses like HIV for infection

The Eukaryotic GenomeMajority of Genome Does NOT

Encode Functional Genes• Pseudogenes are present and considered

evolutionary “leftovers” of once functional genes that have acquired too many insertions or deletions.

• In sea urchins, the 20,000 to 30,000 genes occupy less than 10 percent of the genome.

• In Drosophila, only 5 to 10% of the genome is occupied by encoding sequences.

• In humans, the estimated 20,000 function genes occupy only 2% of the total DNA sequence making up the genome.