What is synteny, and why is it useful in comparative genomics?
ASynteny describes genes with identical sequences in different species
BSynteny refers to conserved gene order and content along chromosomal segments between species
CSynteny means two species have the same number of chromosomes
DSynteny describes the process of genome duplication
Synteny refers to the conservation of gene order along chromosomes between species. If a set of genes appears in the same order on a chromosome in both human and mouse, that region is syntenic. Synteny blocks provide evidence for shared ancestry and reveal where chromosomal rearrangements (inversions, translocations, fusions) have occurred since the species diverged. Synteny is also practically useful: if a gene's function is unknown in one species but known in another, syntenic context and conservation of neighboring genes can inform functional predictions.
Question 2 True / False
Noncoding sequences that are highly conserved across distantly related vertebrates are likely to have no function, since they do not encode proteins.
TTrue
FFalse
Answer: False
Highly conserved noncoding elements (CNEs or ultraconserved elements) are under strong purifying selection — they are preserved precisely because they perform important functions that would be disrupted by mutations. Most are regulatory elements: enhancers, silencers, or insulators that control gene expression during development. Some ultraconserved elements show sequence conservation exceeding that of protein-coding genes, indicating extreme functional constraint. Their functions were originally invisible to gene-centric analyses, and comparative genomics was the approach that revealed their importance.
Question 3 Short Answer
Explain how whole-genome duplication (WGD) events are detected through comparative genomics.
Think about your answer, then reveal below.
Model answer: WGD is detected by identifying blocks of duplicated genes within a genome that show coordinated synteny — many pairs of duplicated genes arranged in the same order on different chromosomes. In a genome that has undergone WGD, you expect to find large-scale 2:1 syntenic relationships (two regions of the duplicated genome corresponding to one region in an outgroup species that did not undergo the duplication). Phylogenetic analysis of gene families should show a burst of gene duplications at the same evolutionary time point, and Ks (synonymous substitution) distributions of duplicated gene pairs should show a peak corresponding to the duplication event.
The teleost fish whole-genome duplication and the two rounds of WGD at the base of vertebrate evolution were established through these methods. Plants show extensive WGD — Arabidopsis has undergone at least three rounds. Over time, many duplicated genes are lost (returning to single copy), but the syntenic patterns remain detectable for hundreds of millions of years.