Ch 12: The Forces of Evolutionary Change (Exam 4) Flashcards
Evolution
descent with modification, inheritance changes in traits from generation to generation
Why does natural selection and evolution act on populations, and not individuals?
-because evolution is a change in allele frequencies, and individuals alleles do not change
Gene Pool
entire collection of genes and their alleles
Explain how Malthus’ ideas were incorporated by Darwin in his development of the concept of natural selection
-Thomas Malthus illustrated that populations produce many offspring and compete for resources-Darwin extended his theory suggesting that those individuals that are able to obtain resources best would be the most likely to survive and reproduce
Artificial Selection vs Natural Selection
Artificial Selection-a human chooses one or a few desired traits, and then allows only the individuals that best express those traits and qualities to reproduce
Natural Selection-occurs when individuals with certain genotypes, those who are best suited for the environment, have a greater reproductive success than other individuals
Explain how the concepts of individual variation in populations, and inertially of variable traits, were used by Darwin to formulate his idea of natural selection
-individual variation in populations mean that some individuals have traits better suited to the environment then others
-inertially of variable traits would be passed down by those who “win” the competition, reproduce, and pass the favorable traits onto the next generation
Adaptations
features that provide a selective advantage because they improve on organisms ability to survive and reproduce
What does it mean when a population is a Hardy-Weinberg Equilibrium?
Hardy-Weinberg Equilibrium-is the highly unlikely situation in which allele frequencies and genotype frequencies do not change from one generation to the next
This can only occur when:
-natural selection does not occur
-mutations do not occur, so no new alleles can arise
-the population is infinity large, or at least large enough to eliminate random changes in allele frequencies
-individuals mate at random
-individuals do not migrate into or out of the population
Contrast Directional, Disruptive, and Stabilizing Selection
Directional Selection-one extreme phenotype is fittest, and the environment selects against the others
Disruptive Selection-(sometimes called diversifying selection), two or more extreme phenotypes are fitter then the intermediate phenotype
Stabilizing Selection-(normalizing selection), occurs when extreme phenotypes are less fit then the optimal intermediate phenotype
Heterozygote Advantage
a circumstance that can maintain a balanced polymorphism, which occurs when an individual with two different alleles for a gene (heterozygote) has greater fitness then those whose alleles are identical (homozygotes)
Examples of sexually dimorphic traits in animals
Sexual Dimorphism- difference in appearance between males and females
Ex: -Female cardinals are brown and males are red
-only male deer have antlers
-only male lions have manes
Explain why increased genetic risk of cancer can only be passed on to offspring if the mutation is present in the parents gene cells
-for example, a cigarette smoker with lung cancer will not pass any smoking induced mutations to their children because her egg cells will not contain the altered DNA
Genetic Drift vs Natural Selection
GD-(sometimes called sampling drift), is a change in allele frequencies that occur purely by chance
NS-causes evolution on the basis of fitness, so it is not random, and it increases diversity
Founder Effect vs Bottleneck Effect
FE- cause of genetic drift that occurs when a small group of individuals leaves its home population and establishes a new isolated settlement
BE-cause of genetic drift that occurs when a populations size drops rapidly over a short period
Explain why low genetic diversity in populations of endangered species is concerning to conservation biologists
-it is concerning because it will reduce population fitness and interbreeding, and can increase extinction risk
-a single change in the environment could doom all species
