We have conducted genetical and cytological analysis of allelic relationships between some phenotypically similar monogenic recessive meiotic mutants in maize.
Table 1. Tests for allelism and segregation pattern of meiosis in meiotic
|Cross||Fertile, regular meiosis||Sterile, irregular meiosis||Fertile, regular meiosis||Sterile, irregular meiosis||X2 9:7||Conclusion|
|dsy2/ dsy2 x dsy A/+||41||0||---||--||not allelic|
|as/as x dsy A/+||4||0||107||97||1.56||not allelic|
|pam A/pam A x pam2/+||2||0||50||39||0.15||not allelic|
|ms4/ms4 x po/+||2||1||allelic|
Allelism was studied between four mutations which impair the pairing of homologous chromosomes and the beginning of meiosis (Table 1). Two desynaptic mutants (dsy A, dsy2) isolated by us in different years from the same line of maize, A344, appeared to be non-allelic. In addition, dsy A was non-allelic to the mutation afd (absence of first division) isolated from W23 (Table 2) and to as (asynaptic), found by G. W. Beadle in 1930 (Table 1). This information confirms other data that the first stages of meiosis are controlled by many different genes.
Table 2. Cytological data on meiotic patterns in
F2 segregants obtained from dsy/+ +/+ x +/+ afd/+ cross
|F2 Segregants Obtained after Self-pollination of F1||Meiotic Pattern|
|Expected genotype Ratios in F1||No. of Families||Fertile||Sterile||Normal||afd||dsy||X2|
|1/4||+ +/+ +||4||343||0||60||-||-|
|1/4||+ +/dsy +||2||84||25||84||-||25||0.95|
|1/4||+ +/afd +||5||346||106||64||23||-||0.13|
|1/4||afd +/dsy +||2||179||141||179||77||64||0.40|
Two mutations causing plural anomalies of meiosis, pam A A344 and pam2 W64A, were also non-allelic (Table 1).
However, possible allelism was found for mutations characterized by precocious postmeiotic mitoses: po (polymitotic), discovered by Beadle in 1933, and ms4, induced with treatment with N-nitroso-N-methylurea by us in A344 line. In po/po plants one or some mitotic divisions take place in sporads having reduced chromosome number (Beadle, 1933). In ms4/ms4 homozygotes the postmeiotic mitoses in the majority of tetrads fail to end; sporads scatter during anaphase and pollen envelopes are formed around them. Meiosis in heteroallelic po/ms4 is similar to ms4/ms4 homozygotes. It is suggested that entrance into the postmeiotic mitoses is controlled by only one recessive gene with a series of alleles.
I. N. Golubovskaya and V. G. Urbach
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