Biology A2 · Selection and evolution. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Members of one species differ from each other. These differences in phenotype come from their genes, from their environment, or from both acting together. Blood group is set by genes alone. Body mass depends on genes and on diet.
In discontinuous variation individuals fall into a few clear groups with nothing in between. It is caused by one gene or a few genes, and the environment has little effect. In continuous variation there is a full range of values between two extremes. It is caused by many genes that each add a small effect, and the environment often changes the result.
The t-test tells you whether the means of two samples are really different or differ only by chance.
Students use s instead of s2 in the t-test formula. Square each standard deviation before dividing by its sample size.
Answer: t = 2.83, so the difference between the means is significant at p = 0.05.
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