A ________ ________ is the combined genetic information of all the members of a particular population. It contains 2 or more alleles for each inheritable trait. The ____________ _____________ of an allele is the number of times that allele occurs in a gene pool compared with the number of times other alleles occur.
The 2 sources of genetic variation are ______________ & ___________________ that results from sexual reproduction.
Natural selection on single-gene traits can lead to changes in _____________ ______________ & thus to evolution. Environmental changes can lead to shifts in gene frequency.
The model of evolution in which gradual change occurs over a long period of time is called _______________. Some biologists believe that there are periods of rapid change in species separated by periods of little or no change. This model is called _____________________ _____________________.
Selection that acts in opposite directions is called _________________ selection. This occurs with the sickle cell gene in Africa. It eliminates variation. ____________________ selection favors one extreme or the other (sickle cell in America). _________________ selection selects against the average & favors extremes (squirrels & acorns).
_______________________ evolution leads to mimicry & occurs when different animals develop similar traits (polar animals). ___________________ evolution leads to speciation & occurs oftentimes when animals are geographically isolated (bears). Coevolution occurs when 2 species evolve together – ex. = ________________.
________________________occurs when there are changes in an individual species over time & ________________________ occurs when several species change (usually due to changes in world climate).
A random change in allele frequency is called ______________ __________. In small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population. This often happens with new habitats. A situation in which allele frequencies change as a result of migration is known as the _______________ _______________.
The ________________________ principle states that allele frequencies in a population will remain constant unless 1 or more factors cause those frequencies to change. This is called _________ _________________. Five conditions are required to maintain this from generation to generation:
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SPECIATION
The formation of new species is called ____________. A species is a group of organisms that breed with 1 another & produce fertile offspring.
As new species evolve, populations become reproductively isolated from each other. When the members of 2 populations cannot interbreed & produce fertile offspring, _________________ ____________ has occurred. The populations then have separate gene pools. There are 3 types of reproductive isolation:
1. ________________ _____________ - 2 populations can interbreed but have differences in courtship rituals or behavior (meadowlarks)
2. ________________ ______________ - 2 populations are separated by geographic barriers (rivers, mountains)
3. _______________ ______________ - 2 species reproduce at different times