Unit 7 AP Bio Study Guide

evolution: change in populations species, or group of species, or the process of which the frequency of heritable traits in a population changes from one generation to the next.

alleles is one of several varieties of a gene, as individuals inherit alleles that code for traits the establish morphology (form or structure), physiology, or behavior. The change of allele frequencies in a population is evolution.

EVIDENCE FOR EVOLUTION:

Paleontology: provides fossils that reveal the prehistoric existence of extinct species (can tell how long a specie has been around) —> C-14 dating, natural decay rate of a radioactive isotope of carbon is used to determine the age of the fossil

Biogeography: use biography to describe the distribution of species, reveals unrelated species in different regions of the world look alike when found in similar environments

Embryology: reveals similar stages in development, help establish evolutionary relationships (phylogeny)

Comparative anatomy: describes the two kinds of structures that contribute to the identification of evolutionary relationships among species

  • Homologous structures (homologies): body parts that resemble on another in different species because they have evolved from a common ancestor.

  • Analogous structures (analogies): body parts that resembles one another in different species, not because they are from a common ancestor, but they evolved independently as adaptations to to their environments.

Molecular Biology: examines the nucleotide and amino acid sequences of DNA and protiens from different species and compare them.

NATURAL SELECTION: the differences in survival and reproduction among individuals in a populations as a result of their interaction with the environment. Some organisms inherit traits called adaptations to the environment that helps them increase their fitness, which is the ability to reproduce.

Natural selection are used by these following arguments:

  • Populations possess an enormous reproductive potential

  • Population sizes remain stable

  • Resources are limited

  • individuals compete for survival

  • there is variation among individuals in a population

  • much variation is heritable

  • only the most fit individuals survive

  • evolution occurs as favorable traits accumulate in the population

stabilizing selection: natural selection favors the intermediate trait

directional selection: natural selection favors the one extreme

disruptive selection: natural selection favors both extremes

sexual selection: a form of natural selection where traits that increase an individuals ability to attract a mate and reproduce, male competition leads to contests of strength that award mating opportunities, while female choice leads to traits or behaviors in males that are attractive to females. Sexual selection often leads to sexual dimorphism, differences in the appearance of males and females.

artificial selection: a form of directional selection carried out by humans when they sow seeds or breed animals that possess desirable traits

SOURCES OF VARIATION:

Mutations: provide the raw material for new variation, can cause different traits to be beneficial

Sexual Reproduction: create individuals with new combinations of alleles, they orginate from three events during sexual reproductive process:

  • Crossing over, exchange of DNA between non-sister chromatids of homologous chromosomes

  • Independent assortment of homologues during metaphase causing daughter cells

  • Random joining of gametes during fertilization

Diploidy: is the presence of two copies of each chromosome in a cell

Outbreeding: mating with unrelated partners, increases the possibility of mixing different alleles and creating new allele combinations

Balanced Polymorphism: the maintenance of different phenotypes in population

  • Heterozygote advantage: occurs when the heterozygous conditions bears a great selective advantage than either homozygous condition, heterozygous has more fitness than homozygous

  • Hybrid vigor (heterosis): describes the superior quality of offspring resulting from crosses between two different inbred strains of plants. basically, the hybrid is more genetically superior than its parents

  • Frequency-dependent selection (minority advantage): Occurs when the least common phenotypes have a selective advantage, but the common phenotypes are selected against.

  • neutral variation: genetic mutations that have no significant impact of an organism’s fitness or reproductive success (ex: fingerprints)

  • Monocultures: the agriculture practice that reduces genetic variation by cultivating large areas dedicated to one crop

  • overuse of antibiotics: reduces variation in bacterial populations by eliminating those individuals that are susceptible to the antibiotics.

CAUSES OF CHANGES IN ALLELE FREQUENCIES:

Natural Selection: is the increase or decrease in allele frequencies due to the impact of the environment

Mutations: introduce new alleles that may provide a selective advantage. In general, however, most mutations are deleterious, or harmful

Gene Flow: describes the movement of individuals between populations, resulting in the removal or alleles from a population when they leave or the introduction of alleles when they enter

Genetic Drift: is a random increase or decrease of alleles

  • the founder effect: occurs when allele frequencies in a group of migrating individuals are, by chance, not the same as that of their population of origin

  • bottleneck: occurs when a population undergoes a dramatic decrease in size, most likely with a natural event

Nonrandom mating: occurs when individuals choose mates based upon their particular traits

  • Inbreeding: occurs when individuals mate with relatives

  • Sexual Selection: occurs when females choose males based upon their attractive appearance or behavior or their ability to defeat other males in contests

HARDY-WEINBURG EQUILIBRIUM:

  1. All traits are selectively neutral (no natural selection)

  2. Mutations do not occur

  3. The population must be isolated from other populations (gene flow)

  4. The population is large (no genetic drift)

  5. Mating is random

SPECIATION: the formation of new species, occurs by the following processes

Allopatric speciation: begins when a population is divided by a geographic barrier so that interbreeding between the two resulting populations is prevented.

Sympatric speciation: is the formation of new species without the presence of a geographic barrier

  • balanced polymorphism: occurs when multiple genetic alleles or phenotypes are maintained within a population at stable frequencies

  • Polyploidy: the possession of more than the normal two sets of chromosomes found in diploid cells. this often occurs in plants.

  • Hybridization: occurs when two distinctly different forms of species mate and produce progeny alone a geographic boundary called a hybrid zone.

Adaptive radiation: relative rapid evolution of many species from a single ancestor. this occurs when the ancestral species is introduced to an area where diverse geographic or ecological conditions are available for colonization.

MAINTAINING REPRODUCTIVE ISOLATION:

prezygotic isolating mechanisms: mechanisms that prevent fertilization

  • habitat isolation: occurs when species do not encounter one another

  • temporal isolation: occurs when species mate or flower during different seasons or at different times of the day

  • behavioral isolation: occurs when a species does not recognize another species as a mating partner because it does not perform the correct courtship rituals, display the proper visual signs, sing the correct mating songs, or release the proper chemicals

  • mechanical isolation: occurs when male and female genitalia are structurally incompatible or when flower structures select for different pollinators

  • gametic isolation: occurs when male gametes do not survive in the environment of the female gamete or when female gametes do not recognize male gametes

postzygotic isolating mechanisms: mechanisms that prevent the formation of fertile offspring

hybrid inviability: occurs when the zygote fails to develop properly and aborts, or dies, before reaching reproductive maturity.

hybrid sterility: occurs when hybrids become functional adults, but are reproductively sterile

hybrid breakdown: occurs when hybrids produced offspring that have reduced viability or fertility

PATTERNS OF EVOLUTION:

divergent evolution: describes two or more species that originate from a common ancestor and become increasingly different over time

covergent evolution: describes two unrelated species that share similar traits, but not become of a common ancestor, but because each species has independently adapted to similar ecological conditions or lifestyles.

parallel evolution: two related species or two related lineages that have made similar evolutionary changes after their divergence from a common ancestor.

coevolution: the process where two or more ecologically interdependent species reciprocally influence each others developments and adaptations