Chapter Thirteen: How Populations Evolve

Questions:

1. What is the Hardy-Weinberg Principle?
2. What are the three main causes of evolutionary change?
3. d

Answers:

1. The Hardy-Weinberg Principle states that allele and genotype frequencies within a sexually reproducing, diploid population will remain in equilibrium unless outside forces act to change those frequencies. 
2. The three main causes of evolutionary change are natural selection, genetic drift, and gene flow.  If individuals differ in their survival and reproductive success , natural selection will alter their allele frequencies.  Genetic drift is a change in the gene pool of a population due to chance.  Gene flow is the movement of individuals between populations and can alter frequencies in a population.
3. d

Key Terms:
Biogeography- the study of the past and present distribution of organisms.
Homology- similarity in characteristics resulting from a shared ancestry.
Microevolution- a change in a population's gene pool over generations.
Mutation- a change in the nucleotide sequence of an organism's DNA.
Paleontologist- a scientist who studies fossils.
Natural Selection- The primary mechanism of evolution producing adaptation of organisms to their environment.
Comparative Anatomy- the comparison of body structures in different species.
Molecular Biology- comparisons of DNA and amino acid sequences between different organisms reveal evolutionary relationships.
Population- a group of individuals of the same species living in the same place at the same time.
Evolution- is the change in heritable traits in a population over generations.

Important Facts:

1. Natural selection can amplify or diminish only heritable traits.  Acquired traits cannot be passed on to offspring.  
2. Evolution is not goal directed and does not lead to perfection, and favorable traits vary as environments change. 
3. Chromosomal duplication is an important source of genetic variation.  If a gene is duplicated, then the new copy can undergo mutation without affecting the function of the original copy.
4. Directional selection acts against individuals at one of the phenotypic extremes.  It is common during periods of environmental change, or when a population migrates to a new and different habitat. 
5. Most animal species show sexual dimorphism, which is when males and females are distinctly different in appearance.