Glossary Plant Breeding

(a) the site of the crossing-over, and (b) the mode of orientation and, thus distribution
of the centromeres of the chromosomes engagedinsomaticcrossing-over. Italways
occurs in the diploid cells. It can be an important source of variation in asexual
pathogenic fungi. It is also thought to be important in allowing recessive cancercausing
mutations to become expressed.
Mixoploidy. A term that covers all types of chimeras in which the heterogeneity between
different elements involves differences in chromosome number (2n = x, 2x, 3x, 4x, 2x-
1, 2x-2, etc)
Mode. The value of the variate, which occurs mostfrequentlyinadataset. Inafrequency
table, the modal class is the class that has the greatest frequency.
Modified Doak Method (Mehta and Patel 1983). A method of producing hybrid seed in
cotton without emasculation. The top portion of the corolla is impressed deeply to
expose only the tip of the stigma. The anthesis is prevented through placing lint
dipped in mud over the remaining portion of the corolla. The stigma is pollinated in
the next morning. The boll setting in crosses has been found greater (specially in the
diploid cotton) than with Doak Method.
Modified Convergent Cross (Mackey, 1954). A convergent cross that involves a very
good variety as persistent crossing partner at every stage of the crossing procedure.
This results in 50% of the genes from the persistent good variety. For example:
A × B A × C A × D A × E
↓ ↓ ↓ ↓
F 1 × F 1 F 1 × F 1
↓
↓
F 1 × F 1
↓
F 1
(50% genes from the parent A)
The procedure can be combined further with different degrees of back crossing
(convergent back cross) of F 1 ’s with the desired parent (A) to ensure even higher
percentage of genes from the very good variety (A).
147