. Principles of modern biology. Biology. Heredity - 485 R gametes R gametes. 75% 25% Fig. 26-9. Cross between yellow- (GG) and green- (gg) seeded garden peas. Due to the dominance of the "yellow gene" (G), heterozygous (Gg) seeds dis- play the same appearance as homozygous (GG) ones. (Fig. 26-9). All the F, yellow seeds belong to the same phenotype (a type of organism judged on the basis of its appearance), but two different genotypes (types based on the genie constitution) are represented. Some of the yellow F2 seeds (Fig. 26-9) are homo- zygous (GG) but others are (Gg), or hetero-
. Principles of modern biology. Biology. Heredity - 485 R gametes R gametes. 75% 25% Fig. 26-9. Cross between yellow- (GG) and green- (gg) seeded garden peas. Due to the dominance of the "yellow gene" (G), heterozygous (Gg) seeds dis- play the same appearance as homozygous (GG) ones. (Fig. 26-9). All the F, yellow seeds belong to the same phenotype (a type of organism judged on the basis of its appearance), but two different genotypes (types based on the genie constitution) are represented. Some of the yellow F2 seeds (Fig. 26-9) are homo- zygous (GG) but others are (Gg), or hetero- zygous; that is, the two genes of an allelic pair are not the same. A dominant-recessive relation between allelic genes is the general rule rather than the exception among animals and plants, al- though frequently the dominance is not al- together complete. When the dominance is complete, as in the present case, the presence of a single recessive gene cannot be deter- mined by the appearance of its possessor, but only by the breeding potentialities. If the recessive gene is present, the correspond- ing trait will turn up in a subsequent genera- tion, as soon as the homozygous condition happens to be established at the conception of some future individual. In other words, although organisms of the same phenotype may look alike, they do not breed alike, unless they also belong to the same Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Marsland, Douglas, 1899-. New York, Holt, Rinehart and Winston
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