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.