15. Genomes and Genomics

When the whole-genome shotgun sequence of the Drosophila genome was assembled, it comprised 134 scaffolds made up of 1636 contigs.

How can sequence gaps be closed?

How do cDNA sequences facilitate gene annotation? Describe how the use of full-length cDNAs facilitates discovery of alternative splicing.

Compare and contrast WGS to a map-based cloning approach.

You have sequenced a 100-kb region of the Bacillus anthracis genome (the bacterium that causes anthrax) and a 100-kb region from the Gorilla gorilla genome. What differences and similarities might you expect to see in the annotation of the sequences—for example, in number of genes, gene structure, regulatory sequences, repetitive DNA?

You have just obtained 100 kb of genomic sequence from an as-yet-unsequenced mammalian genome. What are three methods you might use to identify potential genes in the 100 kb? What are the advantages and limitations of each method?

When comparing genes from two sequenced genomes, how does one determine whether two genes are orthologous? What pitfalls arise when one or both of the genomes are not sequenced?

What is a reference genome? How can it be used to survey genetic variation within a species?

Whole-exome sequencing (WES) is helping physicians diagnose a genetic condition that has defied diagnosis by traditional means. The implication here is that exons in the nuclear genome are sequenced in the hopes that, by comparison with the genomes of nonaffected individuals, a diagnosis might be revealed.

If you were ordering WES for a patient, would you also include an analysis of the patient's mitochondrial genome?

Whole-exome sequencing (WES) is helping physicians diagnose a genetic condition that has defied diagnosis by traditional means. The implication here is that exons in the nuclear genome are sequenced in the hopes that, by comparison with the genomes of nonaffected individuals, a diagnosis might be revealed.

What are the strengths and weaknesses of this approach?

Recall that when the HGP was completed, more than 40 percent of the genes identified had unknown functions. The PANTHER database provides access to comprehensive and current functional assignments for human genes (and genes from other species).

Go to http://www.pantherdb.org/data/. In the frame on the left side of the screen locate the 'Quick links' and use the 'Whole genome function views' link to a view of a pie chart of current functional classes for human genes. Mouse over the pie chart to answer these questions. What percentage of human genes encode transcription factors? Cytoskeletal proteins? Transmembrane receptor regulatory/adaptor proteins?