. Principles of modern biology. Biology. Heredity - 483 Fj sperms B BB black Bb blue b Bb blue bb white sis and fertilization—as may be seen in Fig- ure 26-7. As to feather color genes, each of the Pj fowls can produce only one kind of egg, or sperm, depending on the sex. Conse- quently all F, individuals must be alike; all are heterozygous (Bb) as to the feather color genes. But when the Fj hybrids form gametes, each fowl produces two kinds of gametes in equal numbers. Half the eggs and half the sperm must carry the B gene, and half must carry the b gene. Consequently, depending entirely on t
. Principles of modern biology. Biology. Heredity - 483 Fj sperms B BB black Bb blue b Bb blue bb white sis and fertilization—as may be seen in Fig- ure 26-7. As to feather color genes, each of the Pj fowls can produce only one kind of egg, or sperm, depending on the sex. Conse- quently all F, individuals must be alike; all are heterozygous (Bb) as to the feather color genes. But when the Fj hybrids form gametes, each fowl produces two kinds of gametes in equal numbers. Half the eggs and half the sperm must carry the B gene, and half must carry the b gene. Consequently, depending entirely on the chance union of the gametes, the F2 offspring must be homozygous black (BB), heterozygous (Bb) blue, and homo- zygous white (bb) in a ratio of as is in- dicated in the following Punnett Square: Fj eggs B b F2 zygotes All other matings among Andalusians can be explained by the same mechanism. A blue hen mated to a black cock produces blues and blacks on a 1:1 basis; and similarly a cross between a blue and a white fowl gives blues and whites in a 1:1 ratio (Fig. 26-8). In fact the chromosome hypothesis has been vali- dated by experiments on a countless number of unit hereditary differences, taken singly and in combination, in practically every kind of plant and animal. The results so far indicate that a parent transmits hereditary qualities to the offspring through the agency of discrete material units, called genes, which are borne in the chromosomes of the germ cells. All the di- ploid cells of the organism are equipped with at least two genes that influence the development of any one characteristic. In exerting its effect, each gene maintains a discrete individuality. Its effect upon the or- ganism may be blended with the effects of other genes, but the gene itself is not changed by this association. During meiosis in the succeeding generation, the members of each. Please note that these images are extracted from scanned page images that may have been digitally enh
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