. Principles of modern biology. Biology. Heredity - 487 very simple results, which are easy to analyze —as may be seen in the following experi- ment. Any yellow-seeded F2 pea (Fig. 26-9), which may be either homozygous (GG) or heterozygous (Gg), is backcrossed to a green- seeded (gg) plant and the offspring are ex- amined. If the unknown is of the (GG) geno- type, all the offspring will have yellow seeds, as is shown in Figure 26-9 (the F, genera- tion). But if the unknown is genotype (Gg), only half the offspring will be yellow and the other half will be green, as is shown in Fig- ure 26-10.
. Principles of modern biology. Biology. Heredity - 487 very simple results, which are easy to analyze —as may be seen in the following experi- ment. Any yellow-seeded F2 pea (Fig. 26-9), which may be either homozygous (GG) or heterozygous (Gg), is backcrossed to a green- seeded (gg) plant and the offspring are ex- amined. If the unknown is of the (GG) geno- type, all the offspring will have yellow seeds, as is shown in Figure 26-9 (the F, genera- tion). But if the unknown is genotype (Gg), only half the offspring will be yellow and the other half will be green, as is shown in Fig- ure 26-10. Thus the backcross gives a simple 1:1 ratio, if one deals with a heterozygous individual, as compared to the single product obtained from a homozygous specimen. Dominance does not in any way alter the mechanics of transmission of a gene, but merely changes the potency of the gene as a determinant of developmental processes in the organism. But how the genes, which are transmitted via the zygote to all the cells of the body, manage to produce their profound effects upon developmental processes is a problem that will be discussed later (p. 529). Independent Assortment: Two or More Gene Pairs in Separate Chromosome Pairs. During gametogenesis several or many pairs of chromosomes are "dealt out" simultane- ously to the maturing gametes; and conse- quently it is impossible to predict the exact hereditary constitution of any given egg or sperm. But two or three gene pairs, even if localized in different pairs of chromosomes, can be followed. This permits the hereditary results to be predicted very accurately, as in the following experiment on the inheritance of hair characteristics in guinea pigs. The experiment starts with two well- known laboratory stocks of the guinea pig. One stock with black, smooth hair (Fig. 26- 11) has been inbred for many generations without any change in the color and texture of the coat; and the same is true of the other stock, which has white
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