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F

F, hybrid: offspring produced by crossing parents from strains that have been inbred. They are characterized by having a much greater productivity than either of their parents. Much of the early work on producing hybrids was carried out on corn. It had been known for some time that repeated self-fertilization of corn plants resulted in lower and lower productivity. Part of the reason for this was that a greater proportion of homozygous plants resulted and there was an accumulation of unfavorable recessive alleles. If two such lines of repeatedly self-fertilized plants are developed, it is likely that the unfavorable alleles that accumulate will be different in each case. Neither strain will give a very high yield. If they are now crossed, the off­ spring will be heterozygous for many of these alleles. Since the alleles concerned are recessive, yield will not be depressed. Look at the example below. Assume that each of the recessive alleles shown lowers the yield in the homozygous condition.