Ignore this I messed up

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.  

the answer to the blank provided is “an autosomal gene that is required for the expression of genes on the x chromosome”.

testis-determining factor, abbreviated as td, which is more popularly known as sex-determining region y or sry protein, is a dna-binding protein or  gene-regulatory protein/transcription factor, encoded by the  sry gene. it is the gene responsible for the initiation of male gender determination in humans.

lichens that colonize bare rock secrete acids that break down the rock and start the soil-production process. so they expose rocks