Chapter 27 (A) Flashcards
gene flow
is the movement of alleles between populations.
Gene flow mixes genetic diversity.
Gene flow also keeps the gene pools of two or more populations similar.
Geological timescale as evidence for evolution
History of Earth is divided into eras, periods, and then epochs.
> Fossil record has helped determine the dates.
Two methods are used: Relative dating method & Absolute method
Biochemical evidence for evolution
Evolution is a theory, supported by a large number of observations and experiments
Almost all organisms use the same basic biochemical molecules, including DNA, ATP, and many enzymes.
> Organisms use the same DNA triplet code for the same 20 amino acids in their proteins.
> Humans share many genes with much simpler organisms.
> The diversity of life is due to only a slight difference in many of the same genes.
> The more similar the DNA sequences, the more closely related the organisms are.
gene pool
the sum total of all alleles of all genes in a population.
Relative dating method
Determines the relative order of fossils and strata but not the actual date.
transitional link
Some fossils serve as transitional links between groups.
> Fossils of Archaeopteryx that lived 165 million years ago serve as an example.
>They display an intermediate form between dinosaurs and birds.
> The fossils of Archaeopteryx are similar to other transitional fossils in that they have some traits like their ancestors and others like their descendants, rather than intermediate traits.
founder effect
occurs when a few individuals form a new colony and their collective genes represent only a fraction of the original gene pool.
vestigial structures
Anatomical structures fully functional in one group and reduced or nonfunctional in another.
Example: snakes have no use for hindlimbs, and yet some have remnants of hindlimbs in pelvic girdle and leg.
mutations
are genetic changes that are the only source of new variation in a population.
New mutations can cause allele frequencies in a population to change.
Without mutations, there would be no new inheritable genetic diversity.
Mutations are random events.
Some are beneficial (provide a survival advantage), and some are harmful.
Fossil evidence for evolution
Fossils are remains and traces of past life or any other direct evidence of past life.
> Hard body parts most often preserved: shells, bones, teeth.
»Soft parts can be buried quickly so decomposition is never completed.
>Traces include footprints, burrows, casts.
>Majority of fossils embedded in sedimentary rock.
>Deposited in layers called strata.
Some fossils serve as transitional links between groups.
Fossils of Ambulocetus natans suggest that whales had a terrestrial ancestor.
The five conditions of Hardy-Weinberg Equilibrium and the corresponding deviations from the condition (Table 27.2)
No mutations - mutation
No genetic drift - genetic drift (bottleneck & founder effect)
No migration (gene flow) - immigration/emigration
Random mating - nonrandom mating
No selection - selection
theory of natural selection
Individual organisms in a species exhibit variation that can be passed from one generation to the next.
> Heritable variation.
Organisms compete for available resources.
> Malthus essay that population growth is kept in check due to limits of environment.
Individual organisms within a population differ in terms of their reproductive success.
> Some individuals in a population have favorable traits that enable them to better compete for limited resources.
» Can devote more energy to reproduction and have more offspring.
Organisms become adapted to conditions as the environment changes.
> Natural selection through differential reproductive success shapes traits.
> The result of this descent with modification is adaptation.
Absolute method
Radioactive dating techniques are used to assign an actual date to a fossil.
Technique is based on the half-life of radioactive isotopes.
microevolution
is the change in allele frequencies in a population over time.
Natural Selection
is a process that allows some individuals with an advantage over others to produce more offspring.
Main Types:
stabilizing
directional
disruptive
adaptation
Darwin called the process of adaptation “evolution by natural selection.”
Any evolved trait that helps an organism be more suited to its environment.
population
all members of a species occupying a particular area at the same time and that interbreed and exchange genes.
homologous structure
Anatomically similar because they are inherited from a common ancestor.
Example: human arm and whale forelimb.
continental drift
The positions of continents and oceans have shifted through time.
The distribution of fossils and existing species provides evidence of former positions of continents.
bottleneck affect
occurs following a natural disaster that kills a large proportion of a population.
Evolution
is all the changes that have occurred in living organisms due to differential reproductive success in living organisms over geological time.
Lamark’s proposal of the inheritance of acquired characteristics
The environment can bring about an inherited change
Epigenetic inheritance: chemical modifications to the DNA that occur in one generation may be passed on to later generations.
genetic drift
is a change in allele frequencies of a gene pool due to random meeting of gametes in fertilization.
Genetic drift has greater effects in smaller populations due to fewer gametes assorting.
Bottleneck and Founder Effect
embryological development structure
At some time in development, all vertebrates have a tail and paired pharyngeal pouches.
Reflects common ancestry.
Hardy-Weinberg Equilibrium describes a population in which allele frequencies do not change over time which are never achieved in wild populations.
Allele frequencies in a gene pool will remain at equilibrium, thus constant, in each generation of a large, sexually reproducing population as long as the five conditions are met
Hardy and Weinberg used the equation: p2 + 2pq + q2 to describe the genotype and allele frequencies in a population.
> p2 = frequency of DD genotype.
> 2pq = frequency of Dd genotype.
> q2 = frequency of dd genotype.
theory of evolution
Charles Darwin
This process, called evolution, proposes that species arise, change, and become extinct due to natural, not supernatural forces.
Darwin’s theory of evolution by natural selection explains both the unity and diversity of life on Earth.
> How all living organisms share a common ancestor.
> How species adapt to various habitats and ways of life.
allele frequency
the proportion of each allele in a population’s gene pool.
analogous structures
Serve the same function but not constructed similarly and do not share a common ancestry.
Example: wing of bird and wing of an insect.
Biogeographical evidence for evolution
The first cells evolved in water.
Organisms are composed of 70% to 90% water.
Water is a polar molecule.
Water molecules form hydrogen bonds, which cause them to cling to one another.
Anatomical evidence for evolution and structures (4)
Common descent offers explanation for anatomical similarities among organisms.
homologous
vestigial
embryological
analogous
