Genetic diversity

Natural selection:

This is the process by which certain inherited traits make it easier for organisms to survive and reproduce changing the genetic makeup of populations overtime.

How does natural selection works?

• seperation in population e.g. geographical isolation 
• mutation ----> variation 
• selective pressure for different traits
• the best adapted survive and reproduce/breed 
• pass on their alleles
• changes in allele frequency 
• speciation 

• In order for species to continue their survival, they need to reproduce more. The concept refers to when mates particularly males have to mate with females more often. 

They can do that in the following ways:

• they can become more attractive to the females. For example, the bigger and prettier the peacock, the more likely the peacock would find a mate. 
• intimidating the other same sex rivals. Bigger, stronger mates are choosen 

Artificial selection:  this is when humans encourage and discourage selection of certain traits. 

There are three modes of selection:

• Directional selection: when favoured trait is at one extreme end of the spectrum such as black or white. overtime leads to distinct change in the frequency of the expressed trait in a  population when a single trait is favoured.

• Stabilizing selection: which selects against extreme phenotyoes and instead favours the majority of the well adapted to the environement. 
• E.g: baby weight ----> small- can't survive, large are too dificult to deliver so emedium sized babies are choosen 

• Disrutive selection: when extreme traits at both ends of the spectrum are selected whilst selecting against common traits. 
• In 2008 ---> lake full of crustacians called Daphnia----> yeast parasite. After half dozens of generations, a varience had emerged in Daphnia's response to parasite. some were less suseptible to the yeast but were smaller and had fewer offsprings whilst others were larger and had more offsprings but were more susepticble to the yeast parasite