Evolution and natural selection

4. the change in frequency of an existing gene variant in the population due to random chance.
6. a cell type that does not contain a nucleus and most other membrane-bound organelles.
9. the reduction in genomic variability that occurs when a small group of individuals becomes separated from a larger population.
12. a cell type that does contain a nucleus and most other membrane-bound organelles.
14. the process through which populations of living organisms adapt and change.
15. a large group of single-cell microorganisms.
17. one parent copies itself to form a genetically identical offspring.
18. a branch of science that is related to the formation, growth, and development of embryo.
19. is a method by which a virus can replicate its DNA using a host cell.
20. the repeated evolution of similar traits in independent evolutionary lineages inhabiting similar environments.

1. happens when germs like bacteria and fungi develop the ability to defeat the drugs designed to kill them.
2. the reproduction of viruses using a host cell to manufacture more viruses; the viruses then burst out of the cell.
3. asexual reproduction by a separation of the body into two new bodies.
5. is the complete disappearance of a species from Earth.
7. when a group within a species separates from other members of its species and develops its own unique characteristics.
8. an extreme example of genetic drift that happens when the size of a population is severely reduced.
10. an organism combines the genetic information from each of its parents and is genetically unique.
11. a permanent change in the DNA sequence that makes up a gene.
13. the biological mechanism by which organisms adjust to new environments or to changes in their current environment.
16. one of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location.