. The elements of genetics. Genetics. THE MENDELIAN METHOD in the X, but the two chromosomes never exchange allelomorphs in heterozygous females. The barring gene can be used, therefore, to disthiguish between the X and the Y, and so makes possible the "autosexing" breeds as shown in Fig. ii. O Cf. Fig. II.—The gene for barred feathers (open circle) in poultry expresses itself only partially in females; so suggesting that the Y chromosome carries its non-barred allelomorph (filled circle). Where the basic pigmentation of the birds is brown, rather than black, this ctiect of the Y chr
. The elements of genetics. Genetics. THE MENDELIAN METHOD in the X, but the two chromosomes never exchange allelomorphs in heterozygous females. The barring gene can be used, therefore, to disthiguish between the X and the Y, and so makes possible the "autosexing" breeds as shown in Fig. ii. O Cf. Fig. II.—The gene for barred feathers (open circle) in poultry expresses itself only partially in females; so suggesting that the Y chromosome carries its non-barred allelomorph (filled circle). Where the basic pigmentation of the birds is brown, rather than black, this ctiect of the Y chromosome is clearly detectable by deeper colouration in newly hatched chicks. The combination of the gene for brown pigmentation and that for barring thus gives a true breeding strain of birds in which the sexes are distuiguishablc at hatching by the deeper intensity of down pigmentation, especially round the head, in females than in males. Such a breed is termed auto- scxine. Sometimes, however, as in certain fishes such as Lehistes and in man, the X and the Y chromosomes not only carry the same genes, but also exchange them by crossing-over. These genes, therefore, no longer show complete sex-linkage. Their association with the sex chromosomes is recognizable by the partial, rather than the com- plete, restriction of a particular allelomorph to a particular sex in. 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 Darlington, C. D. (Cyril Dean), 1903-; Mather, Kenneth. New York : Macmillan
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Keywords: ., bookcentury1900, bookpublishernewyorkmacmil, booksubjectgenetics
