Linkage between ms\10 and Wo^m.<p>

Rick, C. M.<p>

The linkage discovered between ms\10 and Wo a number of years ago could not be
exploited in breeding work because of the lethality of the latter gene when
homozygous.  When the Wo^m allele was discovered, the possibility of
exploiting this linkage was reopened and crosses were accordingly made between
the new allele and ms\10.  A large F2 had been grown in 1957 without the
recovery of a single individual showing the recombination Wo/+ ms/ms.  Such a
situation was not unexpected because the linkage distance was known to be very
small.  As the next step to obtain a recombinant, seed was harvested from all
Wo^m/Wo^m individuals (which also were d/d) in this F2.  The F3 progeny tests
were made in 1959, including 80 small families, which were planted at close
spacing in the field.  Segregation was scored in all families for d, Wo^m, and
ms\10.  Three families segregated for Wo^m and were therefore eliminated from
further consideration.  Of the remaining families, 2 segregated for ms\10 and
75 bred true for fertility, all remaining homozygous for Wo^m. For an
estimation of the crossover value, account has to be taken of the small size
of families according to the following calculation.<p>

<pre>
                                                    Effective
                             Non-                      number
Family  Segregating   segregating  P for ms   non-segregating
size       families      families  detection         families
_____________________________________________________________
9                             2      0.925            1.8
10                            7      0.944            6.6
11                1          10      0.958            9.6
12                           17      0.968           16.5
13                1          19      0.976           18.5
14                           20      0.982           19.6

Total             2                                  72.6

</pre>
The following formula can then be applied to calculate the crossover value:
q^2 = 0.973, 2pq = 0.0268, where p = crossover value.  The resulting values,
0.014 and 0.0135, are in remarkable agreement with each other and with
previously obtained values in the neighborhood of one per cent crossingover.<p>

Sib crosses were made between fertile and sterile plants within both
segregating families and seed should have thereby been produced to maintain
the crossover line ms\10-Wo^m for any use that might be made of rapid
backcross incorporation of male sterility into a fertile line.<p>

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