Continuous and noncontinuous traits

Quantitative traits fall into two camps: those that vary continuously and those that don't:

1 Continuous quantitative characters: Quantitative traits often are continuously variable across some range. An example is adult height. Although you may consider yourself to be either tall or short, heights vary smoothly from the tallest to shortest.

1 Non-continuous quantitative characters: Although many multigenetic traits are continuous, some aren't — at least, not in the same way that continuous characters are. Take bristles on fruit flies, for example. Fruit flies have a discrete number of bristles that varies from some bristles to more bristles, but they don't have half a bristle. Your weight can vary by any fraction of a pound (or gram or stone), but a bristle or a pound is either "on" or "off." Some diseases or conditions (those that have two states: sick or not sick) are also non-continuous characters.

The environment has a big impact on many quantitative traits. Taller parents, for example, tend to have taller children, but environmental factors, such as nutrition, also affect adult height.

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