Apopulation of fish in an enclosed lagoon was threatened with overpopulation and a stressed food supply until a number of predators discovered the population. after a time, there were fewer fish, but the average swimming speed of the population of fish had increased. this is a good illustration of .

This is a good illustration of Natural Selection.

Explanation: Also known as (a.k.a.) "survival of the fittest". The fish who are more alert and faster swimmers, will naturally escape capture by the various predators, and continue to live and breed, passing along their genes and characteristics. The slower fish are caught and eaten and are, therefore, unable to breed to pass on their own genes and characteristics. Over time, the concentration of the characteristics that make the fish faster swimmers, is enhanced in the genes of the population, as there is less "watering down" of these genes by the slower swimmers.

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.