LAMPBRUSH CHROMOSOMES AND CHIASMATA OF SEX-REVERSED CRESTED NEWTS

Triturus cristatus carnifex provides a particularly clear example of s exual dimorphism for chiasma frequency and localisation. Oocytes from normal XX females routinely carry one proximal chiasma on each arm of their lampbrush bivalents. Spermatocytes from normal XY males have mor e numerous and relatively distal chiasmata. Lampbrush chromosomes from the oocytes of sea-reversed XY neofemales are found to resemble those from normal oocytes in having one proximal chiasma on each bivalent a rm. A comparison of particular markers on the heteromorphic long arm o f chromosome 1 provides evidence to equate the lampbrush 1A to somatic 1A, and confirms previous reports that lampbrush chromosome 1A is sli ghtly longer than 1B. The XY sex bivalent of neofemales does not show any obvious heteromorphy of recognised marker loops.