Genetic dissection of heterochromatin in Drosophila: the role of basal X heterochromatin in meiotic sex chromosome behaviour.

We have examined the female meiotic behaviour of three X-chromosomes which have large deletions of the basal heterochromatin in Drosophila melanogaster. We find that most of this heterochromatin can be removed without substantially altering pairing and segregation of the two Xs. To compare the role of heterochromatin in male meiosis we have constructed individuals which carry two extra identical heterochromatic mini X chromosomes. These minis behave as univalents even though their heterochromatin is known to contain satellite DNA. We conclude therefore that this satellite DNA is not sufficient to allow effectively normal meiotic behaviour. In all other respects our results in the male extend and confirm Cooper's postulate that there exist specific pairing sites in the X heterochromatin. Thus we find no support in either female or male meiosis for the concenpt that satellite DNA is involved in meiotic chromosome pairing of either a chiasmate or an achiasmate kind.