File:Genetics in relation to agriculture (1918) (20115997463).jpg

Title: Genetics in relation to agriculture
Identifier: cu31924001155310 (find matches)
Year: 1918 (1910s)
Authors: Babcock, E. B. (Ernest Brown), b. 1877; Clausen, Roy Elwood, 1891-
Subjects: Livestock; Heredity; Variation (Biology); Plant breeding
Publisher: New York, McGraw-Hill; (etc. , etc. )
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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MITTATIONS 273 rably associated with variegation. Correns lias pointed out that variegated Mirabilis plants cannot be considered mosaics of green and 'chlorina' types due to heterozygosis, since they do not segregate into chlorina and green, but into variegated and green. The same reasoning applies to variegation in the color of maize ears. Varicgated-eared plants do not throw reds and whites, but reds and variegates. The conclusion seems in-esistible that self-color occurring as a somatic variation is due to the change of a Mendelian factor for variegation into a factor for self-color. If this be granted, the behavior of these variations in later generations is a mere matter of simple )\Iendelian inheritance." If bud sports are caused by mutations and if most bud sports involve a change from the dominant to the recessive condition of a certain factor, it follows that the change in chemical constitution must affect both of the
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Fig. 112.^Bud sport and chimera in an ear of corn. This ear appeared in a field of white dent corn. The apparently white kernels, occupying about 3^ of the surface, wero actually variegated, being marked with "fine red lines, or streaks, radiating from the caps down the sides of the kernels." (After Hartley.) duplex factors present in the somatic cell in order that the recessive character may appear. To those who think of mutations as fortuitous events, this may seem an obstacle to the conception that bud sports are the result of factor mutations. But from the point of view that factor mutations are caused, probably by some specific internal condition, it would seem most natural for the cause to have the same effect on both factors. Obviously this conception assumes that in such cases the specific cause, whatever it is, has the same potentiality in all parts of the nucleo- plasm, and there is no a priori logical objection to such an assumption. At the same time there is good evidence that mutations do sometimes occur in only one of a duplex pair of factors. Hartley reports "a remark- able ear (Fig. 112) occurring in a field of white dent corn which had for many years been grown as a reasonably pure corn, but which occa- sionally, as many white corns do, produced a red ear." But this ear was only partly red since about one-fifth of its surface was occupied by varie- gated grains which appear to be white in the picture. Hartley tested all the grains on this ear and found tha^ the red grains produced a crop of 84 red ears and 86 pure white ears, while the variegated grains 18 Digitized by Microsoft®

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