Homologous bands on the long arms of the X and Y chromosomes of Anopheles atroparvus.

The long arms of the X and Y chromosomes of the mosquito Anopheles atroparvus (2n equals 6) are equal in length, synchronous in their late DNA replication and have homologous G AND Q bands. This indicates that differentiation of the two sex chromosomes was the consequence of a single deletion of an autosome to give the Y chromosome, not followed by the acquisition of differential heterochromatic blocks.