SRY gene (?s?är-w??)n. A gene for maleness found on the Y chromosome. It has a key role in development of the testes and determination of sex.[s(ex-determining) r(egion) Y.]American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.