Eukaryotic Genomes Demonstrate Sequence Organization Characterized by Repetitive DNA

1. Eukaryotic Genomes Demonstrate Sequence Organization Characterized by Repetitive DNA Honors Genetics Lemon Bay High School 2013-2014

2. 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

3. 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

4. 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

6. 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

7. 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.

9. 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.

11. The Eukaryotic GenomeMiddle Repetitive Sequences • Micro-satellites • Short Tandem Repeats • 5 to 50 bp long • Useful molecular markers. • 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

12. 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

13. 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.