Natural selection quiz

Natural selection

The process in which organisms better adapted to their environment tend to survive and reproduce more offspring.

Selective pressure

A factor that either increases or decreases the reproductive success of individuals in a population.

Mutation

A random change in an organism’s DNA sequence.

Allele

One of two or more versions of a gene. For example, there are multiple alleles for the eye color gene. For each gene, an individual inherits one allele from mom and one allele from dad.

Allele frequency

The proportion of a specific allele (variant of a gene) present in a population, essentially indicating how common that allele is within that population.

Genotype

The specific genetic makeup or unique DNA sequence of an organism, representing the particular set of genes or alleles it has inherited from its parents. It defines the potential for traits (ex, BB, Bb, or bb for eye color).

Phenotype

The set of observable traits/the physical expression of an organism’s combination of alleles (ex. eye color, a dog’s herding instinct, blood type, etc).

Adaptation

A) The process by which a species (not individuals) becomes better suited to its environment.

B) A heritable trait that has evolved through the process of natural selection.

Evolution

The process by which the traits of a population of organisms change over generations, driven by natural selection. It results in new traits and potentially new species over time.

Fitness

A measure of an individual’s ability to survive and reproduce in a particular environment.

Gene pool

The combination of all the genes present in a reproducing population. A large gene pool=lots of allele diversity and small gene pool=very little allele diversity. A larger gene pool is also better able to withstand environmental challenges.

Trait

A specific characteristic of an individual determined by genes.

Directional selection

One extreme trait is favored over others in natural selection. The peak shifts to one side of the graph. (Ex. the environment gets colder and animals with lots of fur survive more than animals with no fur).

Disruptive selection

Traits of both extremes are favored, while the middle trait isn’t. Looks like two peaks on each end of the graph. (Ex. food begins growing only on high trees and deep in the ground and animals with either really short or really long necks survive more than animals with middle-length necks).

Stabilizing selection

The middle/average trait isn’t favored, while the extreme traits aren’t. Looks like the peak gets taller and narrower. (Ex. average baby weight is less likely to cause complications than extremely underweight or overweight babies).

Explain how selective pressures make certain alleles more common than others?

1. Population has a variety of genes present (large gene pool).

2. Selective pressure is introduced (drought, new predator, temp. shift, etc).

3. Some individuals have traits made by certain alleles that give them a better chance at surviving the selective pressure.

4. The individuals with these traits survive and reproduce, creating offspring with the same alleles.

5. Over generations, allele frequency shifts and the favored trait becomes far more common than before natural selection.

6. The population looks or acts different because of this change in allele frequency.

Why do non-beneficial alleles not always disappear entirely from a population?

Individuals with one favored allele and one non-favored allele still survive and reproduce, which means they can pass down both the favored and non-favored allele to their offspring. This is how the non-beneficial (non-favored) allele can still survive natural selection, even if it becomes less common.