Cytogenetics of the grasshopper Moraba scurra. 4. Heterozygosity for 'Elastic Constrictions'.

Abstract

In some populations of Moraba scurra Rehn, individuals occur which are heterozygous for chromosomal regions ("elastic constrictions") that become greatly stretched on the spindle of the first meiotic division. Such individuals are always rare (maximum frequency about 1 per cent.) and no individuals homozygous for constrictions have been seen. There are at least three different constrictions-one in the AB chromosome, one in the EF element, and a third in one of the four short chromosomes. The persistence of these structures, which may be short heterochromatic segments of a special type, argues that they are adaptive; but their rarity suggests that homozygotes have a very low viability or fecundity. Similar constrictions have been found in two other species of Morabinae.