. Heredity and evolution in plants . e homo-zygous for one or more characters, and the yield per acremay thus become greatly If now, two of thesesimplified strains, homozygous for many characters, and 1 If both parents have blue eyes the children with rare exceptions haveblue eyes; if one parent has brown eyes and one blue, the children may beboth blue- and brown-eyed, or all brown-eyed, for brown eye-color tendsto be dominant over blue color. When both parents have brown eyes,part of the children may have blue eyes and part of them brown, or theymay all be brown-eyed. As used here,
. Heredity and evolution in plants . e homo-zygous for one or more characters, and the yield per acremay thus become greatly If now, two of thesesimplified strains, homozygous for many characters, and 1 If both parents have blue eyes the children with rare exceptions haveblue eyes; if one parent has brown eyes and one blue, the children may beboth blue- and brown-eyed, or all brown-eyed, for brown eye-color tendsto be dominant over blue color. When both parents have brown eyes,part of the children may have blue eyes and part of them brown, or theymay all be brown-eyed. As used here, the term brown-eyes means alleyes having brown pigment, whether in small spots (gray eyes), or traces(hazel eyes), or generally distributed (brown, or sometimes black, eyes).The term blue eyes designates only those cases in which brown pig-ment is entirely lacking. 2If a high-yielding strain was separated out by selection, the yieldwould of course be increased above the average of the mixed field. AM) EVOLUTION IX PLANTS. EXPERIMENTAL STUDY OF HEREDITY fl having a low yield per acre, are crossed, there results anFI hybrid progeny that is heterozygous for all of thesecharacters. This heterozygosity is correlated with agreatly increased vigor; the plants are much larger, andthe yield per acre is enormously increased (Fig. 43).Thus in one experiment of this kind the average yield ofthe heterozygous horticultural variety was bushelsper acre. After self-fertilization for several generationsthe yield became reduced to bushels per acre; butin the FI generation of a cross between two of these self-fertilized strains the yield per acre rose at once to In the F2 generation the yield again fell to From this, and numerous other experiments, itis found that the biggest corn crop is to be obtained byfinding the strains that will produce the largest yieldwhen crossed, and then using for seed the grains of thefirst-generation hybrids each yea
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