Natural Selection in genes

Single-Gene Traits- Natural selection on single-gene traits can lead to changes in allele frequencies changes in phenotype frequencies.

Polygenic Traits- Natural selection on polygenic traits can affect the distributions of phenotypes in three ways:

1- directional selection- A mode of natural selection in which an extreme phenotype is favored over other phenotypes, causing the allele frequency to shift over time in the direction of that phenotype.

2- stabilizing selection- The population mean stabilizes on a particular non-extreme trait value.

3- disruptive selection- Describes changes in population genetics in which extreme values for a trait are favored over intermediate values. In this case, the variance of the trait increases and thhe population is divided into two distinct groups.


A lizard has extra sticky feet- The places a lizard moves and travels to causes the feet to change over time. Because of its ability to stick to walls and trees it has adapted to the environment with more stick to its foot.

A shrimp that has lost its sight- Over many many years of living in the dark this shrimp has lost its ability to see. It has its other senses to help it navigate.

Owls are changing color- Over many years of hiding from preditors these owls have changed color to blend with their environment

Bedbugs with stronger bodies- These bugs have adapted to resist harsh chemicals.

Mice that resist poison- This mouse now resists the poison Warfarin. This would cause more mice to get into homes.


Trees- Trees have changed in size depending on the environment and animals that eat them.

Tomatoes- The way we grow tomatoes has changed. We now can grow more at a time

Corn- Over the years humans have chemically effected the way corn grows. It now has more nutrition and we can grow more at a time.

Apples- It is thought that the apples we eat today were made from hybridization of other organisms.

Orange- It is a hybrid between pomelo and mandarin. It is thought to have originated from areas in India and China.


Drug Resistant Tuberculosis- Some cases of Tuberculosis have been resistant over the years. One example is in Russia. The persion infected doesn't take the proper amount of medication the infection gets more and more resisrant.

Fungi- Developed in aquatic biotypes, originally from eukaryotic, single-celled organisms called protists. Fungi have no real relation to plants.

Bacteria- Over time bacteria has become resistant to drugs that are used to kill them. Because of this we use stronger doses of the drug that kills them.

Protozoa- These are found as fossils in rocks. The have been extinct for awhile now. They have been described as animal like unicellular eukaryotic organisms.

Viruses- They may have evolved from parts of DNA or RNA that left the genes of a larger organism. They could have also evolved from complex molecules of protein and nucleic acid before cells first appeared on earth.

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