File:Heredity and sex (1913) (14578194789).jpg

Identifier: hereditysex00morg (find matches)
Title: Heredity and sex
Year: 1913 (1910s)
Authors: Morgan, Thomas Hunt, 1866-1945
Subjects: Heredity Sex
Publisher: New York, N.Y. : Columbia University Press
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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n YiG 61 — I. Diagram of five pure lines of beans (A, B, C, D, and E)and a population formed by their union, A-E. II. Diagrams illustrating apure line of beans and two new biotypes derived from it. 1 he upperdiagram indicates the original biotype; the second and third diagram in-dicate the elongated (narrower) and shorter (broader) type of beans Xindicates the average class of the original biotype. (After Johannsen.) SECONDARY SEXUAL CHARACTERS 123 taken for granted that by selecting a particular kindof individual the species will move in the directionof selection. A few examples will bring the matter before us. Ifwe take a peck of beans and put all of those of one sizein one cylinder and those of other sizes in other cyl-inders, and place the cylinders in a row, we get a resultlike that in Fig. 61, A-E. If we imagine a Une joining
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v3d Fig. 62. — The normal binomial curve or the ideal curve of distribu-tion. At the base line, the directions from the average value (o) areindicated with the standard deviation (o) as unity. (After Johannsen.) the tops of the beans, the line gives a curve like thatshown in Fig. 62. This is known as the curve of prob-ability. The curve can be, of course, most readilymade by making the measurements directly. Mostindividuals of such a population will have the charac-ter developed to the degree represented by the highestpoint in the curve. Now if two individuals standingat one side (let us say with the character in questionbetter developed than the average) become the parent 124 HEREDITY AND SEX of the next generation, their offspring will make a hewcurve that has moved, so to speak, in the direction ofselection (Fig. 63). If again two more extreme individuals are selected,another step is taken. The process is assumed to goon as long as the selection process is maintained. So the matt

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