Natural Selection

The members of a species that live in a specific area are known as a _____________. population

There are many different populations in a single ecosystem. Each population of organisms has a ______ to play in the ecosystem. It can be a _________ and eat another species, or it can be the _______ of another predator.

rolepredator

prey

It might recycle nutrients as a decomposer or create sugars as a producer at the foundation of a food chain.

Some organisms, like trees, provide shelter for many different communities.

The role that an organism plays in the ecosystem is

known as its ______.niche

Within a population of organisms, there are many versions of certain ________. There might be more than one version of the gene for hair color, so that some animals are _______ while others are ________ or _______. The different versions of a gene are known as ________.

genes

gray brownwhite

allelesSubject A Subject B Subject C

Genotype for Fur Color

GG Gg gg

Phenotype for Fur Color

Gray Fur Gray Fur White Fur

The ________________ refers to how common a certain allele (version of gene) is within a population. If almost all of the animals in a population have brown fur, than we would say the _______________ for brown fur is high.

frequency

frequency

Random changes in the frequency of an allele occur all of the time. This is known as _____________, and many different things can cause it.

genetic drift

1. Genetic drift can be the result of ________ mating. If a population of plants is mostly tall, it can become shorter and shorter simply by ________. The shift in the frequency of the tall allele is called _____________.

random

chance

genetic drift

2. _________ and ___________ can randomly affect the frequency of a gene. The number of animals in a population with gray fur might be decreased ___________ because of a new virus which killed a large number of animals with gray fur. This change in the frequency of the allele for gray fur is known as _____________.

Plagues epidemics

randomly

genetic drift

3. A small group of organisms from the population might ________ to a new location and start a new population. If the original population was mostly ________ hair, but the new population had an unusually high percentage of _______ haired individuals, then the new population will _______ towards a higher percentage of red hair. This form of genetic drift is known as the ______________.

migrate

brown

reddrift

founder effect

Some alleles make it easier for an organism to _________. Once random ________ has changed in the ___________ of the alleles, the organisms which have the alleles best _________ for the new environment will survive the longest and pass their genes down to their ___________.

survivechance

frequency

adapted

The process of organisms with the best _____________ surviving to pass their ________ down to their offspring is known as _________________.

adaptation genes

natural selection

The _________________ is a classic example of natural selection in action. Before the industrial revolution, the moths were mostly a light grey color which allowed them to hide from __________ by blending in with the bark of trees while dark moths were easily spotted and eaten.

peppered moth

predators

After the industrial revolution began, the _______ soot from the factories began to cover the trees. The grey moths were now easily spotted and eaten by birds, but the few ______ moths were now very well camouflaged.

black

dark

The variation or __________ of the moth community allowed them to survive. The dark moths were now the best adapted and were able to live and reproduce because of the process of ________________. Now most of the moths are _______ instead of the original light grey.

diversity

natural selection

dark

If two populations of the same species become __________ to different environments, the processes of _________________ and _____________ will cause them to change so much that the two populations will become different _________. The process two populations of the same species becoming two different species is known as _____________.

adaptednatural selection

genetic drift

species

speciation

____________ is the study of the relatedness of organisms. This is very closely related to the subject of ____________ which deals with placing organisms into kingdoms.

Phylogeny

taxonomy

Scientists examine organisms and _______ where the process of speciation has occurred. To show these conclusions, they create a diagram known as a __________________.

infer

phylogenetic tree

The organisms which are _________ to each other on a phylogenetic tree are the _______ related. The organisms which are __________ from each other on the tree are the ________ related.

closestmost

farthestleast

In order to draw their conclusions about the relatedness of animals, scientists often compare the _______ found in each organism. If the genes of two organisms are very similar, then the organisms are assumed to be very closely related.

genes

Since the genes in DNA are translated into __________, these are often compared as well as their physical structures or __________. The organisms which are most similar are considered to be the most closely _________.

proteins

anatomy

related

Orangutan Dog Swine Cattle Tapir Horse

Which two organisms are the most closely related? ___________________________________________How can you tell? __________________________________________

Organisms Q and Organism R

They have the most in common!

Most scientists believe that the great variety or ___________ of life on the planet is because of a combination of changes to DNA (called __________ ), changes in the frequency of alleles (called _____________) and the process of the organisms with the best adaptations surviving and having offspring (called _________________).

diversity

mutations

genetic drift

Photo © 2004 Richard Ling

The first life form was believed to be a ___________. This is where the name comes from since pro- is a prefix meaning ________.

prokaryotes

before

The processes of mutation, genetic drift and natural selection are believed by many to have begun with a simple prokaryote and continued over great amounts of time until all of the great variety or __________ of life was formed.

diversityPhoto by Luc Viatour

The theory that a series of random __________ coupled with the process of natural ___________ resulted in all of the life forms on the planet is known as ___________. The first scientist to popularize this idea was named _______________.

mutations

selection

evolution

Charles Darwin

This is why when an organism is very well adapted to a certain environment, scientists assume that it __________ in that environment. If a plant can tolerate snow, then they say that it _________ in a cold environment.

evolved

evolved

It is also why animals with similar characteristics are assumed to have evolved from a _________________. Birds, reptiles, amphibians and mammals are all considered ____________ because they all have a backbone. Scientists assume that all of these very different organisms evolved from a ________________ which had a backbone.

common ancestor

vertebrates

common ancestor