Recombination in Zea Mays

meiotic process in plants or animals does not necessarily produce the same T:!rcentage of recombinants in male and female germ cells. In maize, the frequency of recombination in a particular chromosomal region is usually higher in microsporogenesis than in megasporogenesis, if a difference exists at all. Chromosomes 2 and 10, according to genetic tests thus far, have similar recombination frequencies in both sexes (EMERSON and HUTCHISON 1921 ; BURNHAM 1950; MORGAN 1950; and RHOADES and RHOADES 1939). The Rg-lgz and Rg-d regions studied in chromosome 3 (BURNHAM 1953), the la-su region in chromosome 4 ( BURNHAM 1958), the A,-bt, A,-bm, bt-pr, and bm-pr regions in chromosome 5 (RHOADES 1941 ) , the y-pb region in chromosome 6 (BURNHAM 1953), the gl-Zn region in chromosome 7 (BURNHAM 1950), and the sh-glI5 and wxcwxQo regions in chromosome 9 (NELSON 1964 and 1966) consistently had a higher recombination value when the F, was used as the male parent. The su-gl, (BURNHAM 1958) and su-Tu (EYSTER 1921 and 1922) regions in chromosome 4 have been shown to have similar recombination values in the male and female flowers although the la-su region, which is close to the centromere, showed higher recombination in the male. Various results have been reported for the C-sh, sh-wx, and C-wx regions in chromosome 9 (STADLER 1926; COLLINS and KEMPTON 1927; and BURNHAM 1949 and 1950). Pericentric inversion 5a (5s near centromere, 5L.50) was studied by MORGAN (1950), who reported 12.5% ovule abortion and 28.3% pollen abortion. The differences in abortion percentages were attributed to higher crossing over in the male flowers, which is in agreement with the genetic results of RHOADES (1941) for chromosome 5. When heterozygous for the interchange T5-9a (5L.85, between p r and U , ; 9S.40, proximal to wx) the sh-wx region in chromosome 9 was shown by BURNHAM (1 949,1950, and 1962) to have a higher recombination percentage in microthan in megasporogenesis. Plants which were homozygous for T5-9a or standard normal did not show significant differences. In the C-sh region, studied in the same crosses, there were no differences between the male and female recombination values. BURNHAM (1961) made similar tests between exotic maize stocks and T5-9a carrying sh w x gE,,. The recombination frequency was higher in the male flowers in all tests for the sh-wx region, but the differences were not significant