Powerpoint Feb 3

Learning Objectives

• Explain how non-random mating can also “select” for genetic changes in a population
• Explain what stops non-random traits from going “too far”
• Explain how gene flow introduces or excludes genes from a population and changes the gene frequency
• Explain how gene flow can change the genetic diversity of a gene pool

Sexual selection is a mode of natural selection where typically members of one biological sex choose mates of the other sex with whom to mate (intersexual selection)

• e.g. male peacocks and birds of paradise display for the females to try and attract a mate

OR competition between members of the same sex to sexually reproduce with members of the opposite sex (intra-sexual selection).

• e.g. male rams fight for access to females

Sexual selection (or non-random mating) also “selects” for certain alleles and traits in a population. However, unlike natural selection, the selection is not based on increasing the organism’s chances of survival, but increasing the organism’s chance of reproduction. Traits that are selected for should increase the organism’s fitness. The fitness of an organism is the reproductive success of the organism (the number of offspring that survive to reproductive age). Since these “sexual” traits also increase the organism’s chances at reproduction, the traits are selected for.

This is also why these sexual traits do not become too extreme. Sexual traits that are too extreme may increase the reproductive success, but decreases the chances of survival (e.g. a moose with a horn that is too large will likely be less likely to run away from predators, or it will take more energy to make the horns).

Gene Flow (immigration/emmigration) DOES NOT select for certain alleles and traits in a population. It is simply the movement of alleles from one population to the other. When individuals travel from one population to another, they carry the genetic information (alleles) with them, and adds to the existing alleles in the population (and gene pool). Therefore, the genetic diversity of the populations increase.

• e.g. Dandelion seeds scatter into the wind and carry with them their alleles to another population of dandelions
• e.g. Swedish individuals with alleles that code for blonde-hair and blue-eyes move to India and marry into an Indian family. By immigrating to India, and marrying into the population, the family has essentially contributed their genetic information to the Indian population and increased the genetic diversity.