KNOB-6, A CYTOLOGICAL MARKER FOR CHROMOSOME 6 OF GOSSYPIUM-HIRSUTUM-L
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A cytological marker consisting of a knob of extra chromatin at the end of one arm of a large chromosome was discovered in homozygous condition in a strain of cotton (Gossypium hirsutum) from Uganda. That the knobbed chromosome was large suggested that it belonged to the A genome. Tests with translocations involving A-genome chromosomes suggested that the knob was on chromosome 6. The knob greatly reduces chlasma formation in the arm bearing it but not in the other arm or in other chromosomes. Knob-6 is a useful marker because it is easily maintained in homozygous condition by self-pollination and is readily discerned cytologically. American Genetic Association.