The spelling of the word "tax gene" can be a bit confusing. The word "tax" is spelled with an "x" instead of a "cks" because it comes from the French word "taxe" which is pronounced with an "ks" sound. The IPA phonetic transcription for "tax" is /tæks/. The word "gene" is spelled with a "g" instead of a "j" because it comes from the Greek word "genos" which is spelled with a "g". The IPA phonetic transcription for "gene" is /dʒiːn/. So, "tax gene" is spelled as it is to reflect the origins of both words.