Post on 04-Jan-2016
CHAPTER 23Torpey White
SMALLEST UNIT OF EVOLUTION Natural selection- a process in which
organisms with certain inherited characteristics are more likely to survive.
Natural election acts on individuals, but populations evolve.
Evolution is caused by genetic variation.
SMALLEST UNIT CONT. Microevolution- changes in allele
frequencies over generations. Mutations and sexual reproduction
contribute to variations in individuals in a population.
23.1 MUTATION AND SEXUAL REPRODUCTION Gregor Mendel- theorized that traits
were passed on through genes Traits differ from person to person. Genotypic properties are passed down,
not phenotypic.
VARIATION IN POPULTIONS Heritable variation is caused by the
passing of quantitative characters. Quantitative characters- heritable
features in populations that vary based on environmental factors and multiple genes accounting for one phenotypic expression.
Measured with average heterozygosity- the average percent of loci that are heterozygous.
Cline- gradual changes of phenotypes that changes with geography
VARIATION BETWEEN POPULATIONS geographic variation- differences in the
genetic composition of separate populations.
Mutations alter genes and in turn alters phenotype. Can be a positive or negative mutation.
Mutations occur at random. Point mutation- the change of one base
in a sequence Large mutations are usually harmful.
SEXUAL REPRODUCTION Variation in populations that reproduce
sexually results from the combinations of genes between parents.
This variation is caused by shuffling, crossing over, independent assortment, and fertilization.
23.2 HARDY WEIN-BERG
GENE POOLS AND ALLELE FREQUENCIES Population- localized group of
individuals that are capable of having viable offspring
Gene pool- the compiled genetic information of a population
Hardy Wein-berg problems deal with allele frequencies in populations.
640 red flowers in a population of 1000, frequency of allele would be .8
HARDY WIEN-BERG PRINCIPAL Used to study the genetic makeup of a
population that is not evolving. Used to track evolution. 5 conditions need to be met
No mutations Random mating No natural selection Extremely large populationNo gene flow
23.3 NATURAL SELECTION,
GENETIC DRIFT, AND GENE
FLOW
GENETIC DRIFT Genetic drift- flocculation of gene
frequencies from one generation to the next.
Genes can be lost randomly through genetic drift.
Two types of genetic driftFounder effectBottleneck effect
FOUNDER EFFECT Founder effect- when a few individuals
become isolated from a larger population
Gene pool of smaller group is normally not representative of the larger population.
BOTTLENECK EFFECT Bottle neck effect- when a drastic
change in environment reduces the gene pool of a population
Same results as the founder effect
GENE FLOW Gene flow- the movement of alleles
among populations Alleles are transferred through gametes Gene flow makes populations more
similar Gene flow is more likely to cause
variation than a mutation
23.4 NATURAL SELECTION
CAUSING EVOLUTION
RELATIVE FITNESS “Survival of the fittest” is misleading,
implies that natural selection is a direct competition.
Natural selection is caused by sexual reproduction, not competition.
Relative fitness- contribution one individual makes to the next generation. How effectively they passed on their genes.
NATURAL SELECTION Directional selection- selecting at one
end of the phenotypic range Disruptive selection- selecting at both
ends of the phenotypic range Stabilizing selection- selecting in the
middle of a phenotypic range
SEXUAL SELECTION Sexual selection- a form of natural
selection where mates are picked for exhibiting specific traits
Sexual dimorphism- marked differences between sexes.
Intrasexual selection- individuals competing for mates. Male v male or female v female
intersexual selection- individuals chose mates vs. competing.
THE ONE EXPERIMENT IN THE CHAPTER Female frogs preferred long calls over
short calls. The genetic makeup of the genes for calls were compared. Info for short calls was put with eggs that had long call info. It was shown that lc individuals had a better chance for survival. They concluded lc gene allowed for better survival.
BALANCING SELECTION Balancing selection- when natural
selection maintains two forms in a population.
Includes heterozygous advantage Heterozygous advantage- when
heterozygotes have a greater fitness than either homozygote.
FREQUENCY DEPENDANT SELECTION Frequency dependant selection- when
the fitness of an allele declines when it becomes too popular.
PRACTICE HARDY WIEN-BERG In a population of moose, lime green fur
is dominant over orange fur. Out of 500 individuals, 370 have, and are homozygous for, lime green fur. Calculate the frequency of each allele and estimate the number of individuals who are heterozygous and homozygous recessive.