. Animal biology. Biology; Zoology; Physiology. 290 ANIMAL BIOLOGY. Aside from his masterly foresight in realizing that success de- pended on simplifying the problem by dealing with definite al- ternative characters, Mendel's claim to fame lies chiefly in his P discovery of a simple principle by which the results may be ex- plained. Since the hybrids when inbred always give rise to hybrids and also to each of the parental types in a pure form, it must be ]? that the factors (genes) which de- termine the characters in question are sorted out, or segregated, in the ripe germ cells, or gametes. A
. Animal biology. Biology; Zoology; Physiology. 290 ANIMAL BIOLOGY. Aside from his masterly foresight in realizing that success de- pended on simplifying the problem by dealing with definite al- ternative characters, Mendel's claim to fame lies chiefly in his P discovery of a simple principle by which the results may be ex- plained. Since the hybrids when inbred always give rise to hybrids and also to each of the parental types in a pure form, it must be ]? that the factors (genes) which de- termine the characters in question are sorted out, or segregated, in the ripe germ cells, or gametes. Assuming for illustrative purposes that a single gene determines a given character, it follows that after segregation the genes are F2 distributed so that some gametes bear the gene for one character and other gametes bear the gene for the other character, but no gamete ever bears the genes for both characters. If the gametes of the Fig. 181B. — Diagram of a Men- . . _. , delian monohybrid. Results of cross- original tall parent contained the ing tall (S) and dwarf (s) Pea plants, gene for tallness (S), and those The circles represent the zygotes and of the dwarf Qt the for the characters ot the soma (pheno- x . type); the letters within the circles, dwarfness (s) - - then the hybrids the germinal constitution (genotype), will arise from a zygote which The letters outside the recombination combines both genes (&), and square represent the gametes. JNote . ° that each of the parents (P) repre- since tallness is dominant over sents a different phenotype and gen- dwarf ness all will be tall. Further, otype; all the F, (one shown) belong when the ceUg of thig h brfd to the same phenotype and genotype; while the F2 represent two pheno- (Ss) mature, and these genes are types and three genotypes. The rel- segregated SO that half of the ative number of individuals compos- gametes bear S and half bear S, mg the 12 phenotypes is 3 :1. ° . , then when such plants, each with this ge
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