. La biologie et l'homme. Biologie ; les êtres humains. 100- 90 Les droits de taille 80 70 60 50 40 30 20 10 0 D-. B D E FACTEURS multiples dans la stature d'une personne à l'héritage est représenté, sur une échelle de pourcentage, de la somme de quatre seg- ments, la longueur de chacune d'elles devant être déterminé par indépendamment des facteurs héréditaires. Les proportions moyennes d'^le jour segments sont indiqué en A. Les extrêmes pour le segment de tête-cou sont indiqués à l'B, ceux de l'agrégation sur C, et ainsi de suite. On n'hérite pas six agilité, ou même tallness ou essoufflement, comme un simple trait. Plusieurs facteurs indépendants l'un hérite qui, agissant ensemble, r

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. Biology and man. Biology; Human beings. Human stature 100- 90 80 70 60 50 40 30 20 10 0 d-. B D E MULTIPLE FACTORS IN INHERITANCE A person's stature is represented, on a percentage scale, as the sum of four seg- ments, the length of each being determined by independently inherited factors. The average proportions of ^the Jour segments are shown at A. The extremes for the head-neck segment are shown'at B, those for the trunk at C, and so on. One does not inherit six-footedness, or even tallness or shortness, as a simple trait. One inherits several independent factors which, acting together, result in a man's being 5 feet 6 inches or 6 feet 1 inch. (Based on data from C. B. Davenport) When Mendel made his experiments, little was known about the nucleus of cells, and nothing about the behavior of chromosomes during cell-division. To explain his findings, however, Mendel made certain suppositions, or guesses, about what probably goes on as eggs and sperms are being formed. And his suppositions turned out to agree in some ways remarkably well with the facts (see illustration opposite). Nuclear Division We have already seen that when germ cells (eggs and sperms) are being formed, the number of chromosomes becomes reduced to half the number present in each body cell. When a sperm cell unites with an egg cell in fertilization, the resulting zygote contains the full number of chromosomes. Half of these came from the male parent and half from the female parent (see illustration, p. 376). If we suppose that the chromosomes bear Mendel's assumed "determiner", the behavior of the chromosomes fits in astonishingly with the facts found by Mendel and other experimenters. This was pointed out by an American biologist, W. S. Sutton. The facts of 484. 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 work.. Grue

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