BIO 263 Lecture Notes - Lecture 12: Directional Selection, Birth Weight, Pleiotropy
Document Summary
Type of selection which most people think of when national selection is mentioned. Something occurs which leads a change in average value. In this case this leads to lowering variation instead of increasing variation like which is normally believed. However the mean would increase instead of decreaseing. This form of selection can allow a single gene allele to even become fixed or lost over time. Example of this selection is in cliff swallows. A shortage in population lead to the decrease in bird population where it happened to be that the larger body size ones lived compared to the smaller sized swallows. Decreases the population on both extremes when compared to normal distribution. Example is found in our own species in case of birth weight. Average baby weight size has the lowest mortality therefore this leads to most babies being born much more near the average than compared to the extremes.
