Introduction to Genetic Analysis 61

Introduction to Genetic Analysis 61 - 60 Chapter 2 Patterns...

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Unformatted text preview: 60 Chapter 2 Patterns of Inheritance which) would have white fat and the other yellow. Luckily, this was not done, and the same animals were bred again, leading to a very interesting, different result. Often in science, an unexpected observation can lead to a novel principle, and rather than moving on to some- thing else, it is useful to try to explain the inconsistency. So why did the 3:1 ratio disappear? Here are some pos- sible explanations. First, perhaps the genotypes of the parental animals had changed. This type of spontaneous change affecting the whole animal, or at least its gonads, is very unlikely, because even common experience tells us that organ- isms tend to be stable to their type. Second, in the repeat, the sample of 22 F 2 animals did not contain any yellow simply by chance (bad luck). This again seems unlikely, because the sample was quite large, but it is a definite possibility. A third explanation draws on the principle covered in Chapter 1 that genes do not act in a vacuum; they de- pend on the environment for their effects. Hence, the useful catchphrase Genotype 1 environment...
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