Eukaryotic Test 3 Lecture 7

The unique content of genetic info that each species has, which is equivalent to all the genetic info that is present in a haploid

For humans, the genome is the genetic info in a single set of chromosomes including 22 autosomes and both X & Y sex chromosomes

DNA's ability to separate into its 2 component strands

As the 2 DNA strands separate, hydrophobic interactions are greatly decreased, changing electronic nature of the bases and increasing their absorbance of the UV radiation

Melting Temp.: The temp. at which the shift in absorbance is half completed

Melting Temp. is related to the GC content of DNA molecule. The higher the GC content, the higher the (Tm) because GC pairs have an extra hydrogen bond between the bases

Complementary single stranded DNA are capable of reassociating

• It is:
• 1. The basis for an investigation into the complexity of the genome

2. The basis for nucleic acid bybridization

• Ionic strength of the solution
• Incubation temperature
• Concentration of DNA
• Period of incubation
• Size of the interacting molecules

A simple genome has a single, symmetrical curve of renaturation

Renaturation of eukaryotic genomic DNA has a curve showing 3 more or less distinct steps because of the presence of 3 broad classes of DNA sequences

• 1. Highly repeated fraction
• 2. Moderately repeated fraction
• 3. Nonrepeated fraction

Present in at least 10^5 copies/genome, ~1-10% of total DNA, short DNA sequence repeat itself in tandem

3 Overlapping Categories:

1. Satellite DNAs: Consists of short sequences (5-~100's) forming very large clusters, each containg up to several million base pairs of DNA

2. Minisatellite DNA sequences: Range from 12-100 base pairs & found in clusters containing as many as 3000 repeats

3. Microsatellite DNA: Shortest sequences (1-5 bp long) & typically present in small clusters of ~10-40 bp in length

Repeat win the genome a few to ten of thousands of times. ~20-80% of total DNA depending on the organism

1. Repeated DNA sequences w/coding functions: Genes that code for Ribosomal RNAs and histones

2. Repeated DNAs lacking coding function: Occur as clusters of tandem sequences, members of these families scattered (interspersed) thruout genome as individual elements

• SINES: short interspersed elements
• LINES: long interspersed elements

Localized to a particular site on a particular chromosome. Contain greatest amount of genetic info & code for all proteins except histones

Genes that code for polypeptides are usually members of a family of related genes

Genome relatively stable but capable of rapid change from 1 generation to the next & w/in 1 lifetime

Whole-Genome Duplication (Polyploidization): Offspring are produced having 2X the # chromosomes in each cell as their diploid parents. Offspring have 4 homologues of each chromosome

• 1. 2 related species mate to form a hybrid organism (often in plants)
• 2. A single-celled embryo undergoes chromosome duplication w/out cell division & develops into a viable embryo (Often animals)

Gives an organism remarkable potential if it can survive the increased # of chromosomes & reproduce.

• Extra copies of a gene can be:
• 1. Lost by deletion
• 2. Inactivated by deleterious mutations
• 3. Evolved into new genes that possess new functions

*Duplication of a small portion of a single chromosome, produced by a process of unequal crossing over

• Vast majority of gene duplicates are:
• 1. lost thru deletion
• 2. inactivated by unfavorable mutation

A small % acquire favorable mutations allowing extra copy to find a new function, or both copies may undergo mutations & evolve into more specific functions

Evolutionary relics whose function has been inactivated by severe mutations

Transposable Elements: Certain genetic elements capable of moving from one place in a chromosome to a diff. site

Transposons: Bacteria containing transposable elements

1. Can (on occasion) carry adjacent parts of the host genome as they move from 1 site to another

2. DNA sequences origianally derived from transposable elements are found as part of eukaryotic genes

3. In some cases, transposable elements appear to have given rise to genes, themselves