The words genes, jeans sound the same but have different meanings and spellings. Why do genes, jeans sound the same even though they are completely different words?
The answer is simple: genes, jeans are homophones of the English language.
Plural form of gene.
Plural form of Jean.
A patronymic surname derived from a medieval variant of John.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").