CHROMOSOME COILING IN RELATION TO MEIOSIS AND CROSSING OVER

Abstract

URING the past five years a considerable amount of evidence has D been obtained which strongly supports JANSSENS' partial chiasmatypy theory of chiasma 'formation.This evidence includes (I) the meiotic configurations found in trivalents and quadrivalents (DARLINGTON 1930) ; (2) the frequency of figure-8 chromosomes in segmental interchange rings of Pisum (SANSOME 1933); (3) the relation between the failure of chiasma formation and absence of crossing over (DOBZHANSKY 1932), BEADLE 1933) ; (4) the relation between chiasma frequency and crossover frequency (BEADLE 1932, DARLINGTON 1934) ; (5) the similarity in effect of environment on chiasma frequency and crossover frequency (WHITE 1934) ; (6) the behavior of heteromorphic homologues (HUSKINS and SPIER 1934); ( 7) the evidence for interference in both chiasma formation and crossing over (HALDANE 1931) ; (8) the negative correlation of frequencies for both chiasmata and crossing over in bivalents of the same cell (MATHER and LAMM 1935); (9) the types of chromatid associations a t meiosis (HEARNE and HUSKINS 1935); and (IO) the types of interlocking between non-homologous bivalents a t meiosis (HUSKINS and SMITH 193 5, MATHER 1935).Some of this evidence can not be considered as critical, because its