Genomics

Genomics Overview

  • Definition: Study of an organism's genome, which includes the complete set of DNA, and its functions, evolution, and interactions with the environment.

  • Nature: Multidisciplinary field utilizing lab and bioinformatic techniques.

Mapping Genomes

Techniques to Analyze Genomes

  • Genomics utilizes various approaches to analyze entire genomes.

Types of Maps

  • Genetic Maps: Linkage maps indicating relative gene locations based on recombination frequency.

  • Physical Maps: Provide absolute gene locations using DNA sequence landmarks.

Physical Maps

  • Base Pair Measurement:

    • 1000 base pairs (bp) equate to 1 kilobase (kb).

  • Physical mapping can occur without prior knowledge of DNA sequences or gene encoding.

  • Types of Physical Maps:

    • Restriction Maps: Based on distances between restriction sites.

    • Chromosome Maps: Depict chromosome-banding patterns.

    • Sequence-Tagged Site (STS) Maps: Measure distance on DNA molecules using tagged sequences.

Restriction Maps

  • Overview: First physical maps based on distances between restriction sites.

  • Contigs: Overlapping smaller segments can be assembled into continuous segments of the genome.

Chromosome Maps

  • Creation: Use stains producing consistent bands on chromosomes, aiding in dividing them into subregions.

  • Fluorescent In Situ Hybridization (FISH): Tagging cloned DNA to cytological maps for analysis.

In Vitro Replication of DNA

  • Polymerase Chain Reaction (PCR): Amplifies DNA, yielding over a billion copies after 30 cycles.

Sequence-Tagged Site (STS) Maps

  • Definition: Unique genomic DNA stretches amplified by PCR.

  • Mapping Process: Assesses proximity of STS markers to infer closeness on DNA fragments, facilitating genome assembly.

Correlation of Genetic and Physical Maps

  • Helps scientists to determine the sequence of genetically mapped genes, overcoming resolution challenges of genetic maps versus genomic sequences.

Genetic Maps

  • Genetic maps are stored in databases such as the National Center for Biotechnology Information (NCBI).

  • Similar databases exist in Europe and Japan.

Whole Genome Sequencing

  • The ultimate physical map is the complete base-pair sequence of the genome requiring high-throughput automated sequencing and computer analysis.

Sequencing Methods

Dideoxy Terminator Sequencing

  • Method: Uses dideoxynucleotide chain terminators (ddNTPs) for DNA synthesis, reading sequence through capillary tube electrophoresis.

Next-Generation Sequencing

  • Advancements: Faster and more cost-effective sequencing technologies; allows simultaneous reactions without genomic libraries.

Genome Sequencing Details

  • Sequencing achieves accurate segment sequences up to 800 bp; 5-10 genome copies are utilized to minimize errors using cloning vectors like YACs, BACs, and HACs.

Human Genome Project Overview

  • Launched in 1990; resulted in a draft sequence published by both public and private entities by 2001, with a refined sequence in 2004.

  • Final sequence: 3.2 billion base pairs, with decreased gaps and high accuracy.

Findings from the Human Genome Project

  • Discovered fewer genes (approx. 25,000) than previously estimated (100,000).

  • Complexity of an organism isn't solely determined by gene quantity.

Gene Identification Techniques

Open Reading Frames (ORFs)

  • Identified by a start codon and a continuous stretch without stop codons.

BLAST Search Algorithm

  • Used to find homologous gene sequences, aiding in inferring functions of molecular clones.

Genome Organization

  • Comprises:

    • Coding DNA: Contains genes that encode proteins.

    • Noncoding DNA: Regions that do not encode proteins.

Classes of Coding DNA in Eukaryotes

  • Single-Copy Genes: Predominantly represented.

  • Segmental Duplications: Blocks of genes from one chromosome to another.

  • Multigene Families: Groups of similar genes.

  • Tandem Clusters: Identical gene copies within close proximity.

Noncoding DNA in Eukaryotes

  • Majority of the genome consists of noncoding sequences, including introns, structural DNA, SSRs, pseudo genes, and transposable elements.

Transposable Elements (Transposons)

  • Types: Include LINEs, SINEs, LTRs, and dead transposons.

  • Make up a significant portion of noncoding DNA.

Comparative Genomics

  • Studies whole genome maps of organisms, revealing evolutionary relationships and conserved gene orders (synteny).

Functional Genomics

  • Investigates gene functions and products using DNA microarrays for gene expression analysis.

Proteomics

  • Study of the entire set of proteins expressed by a genome, revealing complexities like alternative splicing and post-translational modifications.

  • Post translational modification

  • Alternativ splicing

Applications of Genomics

  • Revolutionizes aspects such as diagnostics, agriculture, and clinical genetics.

  • Ethical considerations include gene patents and privacy in genetic information handling.