. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. THE STATISTICAL STUDY OF VARIATION 35 From Fig. 15 it is evident that as n becomes larger tlie straight lines of the polygon more closely approximate the normal curve. The normal curve is perfectly symmetrical because it represents the distribution of an indefinitely large number of items and it assumes all causes to be of equal strength or value. It is assumed that certain biological frequency polygons should simulate this curve for these reasons. It is probable that the environment of any organis
. Genetics in relation to agriculture. Livestock; Heredity; Variation (Biology); Plant breeding. THE STATISTICAL STUDY OF VARIATION 35 From Fig. 15 it is evident that as n becomes larger tlie straight lines of the polygon more closely approximate the normal curve. The normal curve is perfectly symmetrical because it represents the distribution of an indefinitely large number of items and it assumes all causes to be of equal strength or value. It is assumed that certain biological frequency polygons should simulate this curve for these reasons. It is probable that the environment of any organism is made up of a large number of factors each of which may vary around a mean independ-. FiG. 15.—Polygons representing expansion of the binomials (a + b)* and (a + b)'" as compared with the normal curve. ently of the others. Now if a frequency polygon is to be made regarding a character of a population composed of individuals alike in zygotic constitution, such as a field of potatoes of the same variety, the differences found in the development of any character are due wholly to these en- vironmental factors. Hence it is likely that the mean of the distribution is made up of observations on individuals upon which an equal number of favorable and unfavorable forces have acted and the deviates are those upon which a greater or less number of favorable or unfavorable forces have acted. But in sexually reproduced allogamous species the in- dividuals are not alike in zygotic constitution. Moreover, the causes affecting a given character may have an unequal mass effect according to ecological conditions. Either of these factors may cause a high degree of asymmetry in a polygon of variation. Graphs in which the mode is rather far removed from the mean are called skew polygons or curves. Digitized by Microsoft®. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illust
Size: 1414px × 1766px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksu, booksubjectplantbreeding
