The difference in the conservation scores, for both PhastCons and PhyloP, is that the wiggle database format (from which the details page and Table Browser scores are extracted) uses lossy compression that keeps enough resolution to display the pixelated scores in the browser graphic display but does not reconstruct the true original scores. This is why we make the original score files available for download.
To access the UCSC Genome Browser programmatically and bypass the CAPTCHA, all requests must -include an API key. Note than an API key is not needed to use our REST API.
To generate your own key, first log in with your UCSC Genome Browser account. Once logged in, go to the Hub Development page and generate a key from the API key section at the bottom of the page.
The key must be appended to your request URLs using the apiKey= variable.
Separate it from other URL parameters with an ampersand (&). For example, most queries will
work by adding apiKey=YOUR_UNIQUE_KEY to the end of the URL:
https://genome.ucsc.edu/cgi-bin/hgTracks?db=hg38&apiKey=YOUR_UNIQUE_KEY
If you experience any issues using the API key, please contact us.