. Adventures with animals and plants. Biology. 470 Orgams?HS Are Products of Heredity and E7iviron?nent unit ix. Fig. 419 The guinea pigs at the left were the parents of those at the right. Were the parents pure black or hybrid? Explain, (castle's genetics and eugenics) Mendel's law of segregation is truly a law, for it holds for all of the plants and animals which have been studied. There are many. Among others tobacco, corn, Jimson weed, squash, and snapdragon have received much attention. Among animals studied extensively are rats, mice, cattle, rabbits, fowl, dogs, cats, horses, insects, f
. Adventures with animals and plants. Biology. 470 Orgams?HS Are Products of Heredity and E7iviron?nent unit ix. Fig. 419 The guinea pigs at the left were the parents of those at the right. Were the parents pure black or hybrid? Explain, (castle's genetics and eugenics) Mendel's law of segregation is truly a law, for it holds for all of the plants and animals which have been studied. There are many. Among others tobacco, corn, Jimson weed, squash, and snapdragon have received much attention. Among animals studied extensively are rats, mice, cattle, rabbits, fowl, dogs, cats, horses, insects, fishes, and man himself. But the animal with which most experiments have been performed is the fruit fly (Drosophila melanogaster). The famous fruit fly. The fruit fly is a tiny fly frequently found near ripe fruit. You can show by diagrams the results of one crossing of the fruit fly. See Exer- cise 13. Its heredity has been studied in laboratories all over the world because it is particularly suitable for such work. It is small, needs little food, and is easy to raise. Its life cycle takes only two weeks, so 25 generations can be studied in one year. There are about 400 ofi^- spring from one mating; these large numbers give us reliable ratios. Then, too, it has a relatively small number of chromosomes, only four pairs, each pair difi^ering from the others in size and shape. Biologists probably know more about the heredity of the fruit fly than of any animal or plant. Morgan and his students and fellow workers suc- ceeded in developing a map of its chro- mosomes, showing at which point each kind of gene must lie. Innumerable experiments with the fruit fly have shown that in the inher- itance of some characters there is domi- nance, in others there is blending inher- itance. But no matter which character is studied, the law of segregation holds. Can you explain the results indicated in Figure 422? See also Figure 420. (Optional) Two pairs of characters. Mendel asked himself this
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