. Principles of modern biology. Biology. RESULT: IDENTICAL TRIPLETS (Always of same sex) /q\ Two separate sperms fertilize ^-^ two separate eggs. RESULT: Triplets, two of whom are really identical twins, the other a fra- ternal twin of theirs, of the same or opposite sex. (q) A third type, of "unmatched" triplets, can result from the ~ three separate sperms and three separate eggs. he union of Fig. 26-25. (From Scheinfeld, You and Hered/'/y. Permission of J. B. LippincoM Co.) MULTIPLICITY OF GENIC EFFECTS Each part and characteristic of an organ- ism is usually affected not by a sing
. Principles of modern biology. Biology. RESULT: IDENTICAL TRIPLETS (Always of same sex) /q\ Two separate sperms fertilize ^-^ two separate eggs. RESULT: Triplets, two of whom are really identical twins, the other a fra- ternal twin of theirs, of the same or opposite sex. (q) A third type, of "unmatched" triplets, can result from the ~ three separate sperms and three separate eggs. he union of Fig. 26-25. (From Scheinfeld, You and Hered/'/y. Permission of J. B. LippincoM Co.) MULTIPLICITY OF GENIC EFFECTS Each part and characteristic of an organ- ism is usually affected not by a single pair of genes, but by several or many pairs. There are, for example, at least 50 different genes that are known to have an influence upon the eye color of Drosophila; and under natu- ral breeding conditions, all these different genes cooperate in determining the eye color of the individual offspring. A cross between the red-eyed and white- eyed flies can be called a "one-factor cross" only when the original Pt stocks are homo- zygous and similar as to all other gene pairs having any influence on the eye color. Delib- erately, the stocks selected for most genetic experiments differ from each other by only one or two hereditary factors; and a long preliminary process of inbreeding is neces- sary to secure such stocks. In a sense, there- fore, the breeding experiments of the labora- tory geneticist, which yield such simple ratios among the offspring, are somewhat artificial and arbitrary. Wild flies, obtained directly from their natural habitat, tend to be hetero- zygous for many genes. Consequently many different recombinations appear among the offspring. Under these conditions, it is not possible to predict the results of a given mat- ing very accurately. Without the inbreeding technique, therefore, geneticists might not have been able to ascertain the mechanism of heredity, except among a minority of. Please note that these images are extracted from scanned page im
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