Unit 3 Flashcards
Evolution
xwhat are the 5 sources of evidence of evolution
- Fossil record
- Biogeography
- Anatomy
- Embryology
- DNA
- Evidence from the fossil record
provides evidence
- fossils closer to the surface are more similar to species that are alive today compared to those deeper
- fossils appear in chronological order in rock layers
TRANSITIONAL FOSSILS: show intermediary links between groups of organisms
- this helps scientists better understand evolution and relationships between organisms
- transitional fossils link the past with the present
- Evidence from Biogeography
- study of the past and present geographical distribution of organisms
- geographically close environments are likely to be populated by related species than similar environments that are separate
Evidence from Anatomy
- vertebrate forelimbs can be used for flying, running, and swimming
- although they have different functions, they all have the same set of bones all organized similarly
- the basic vertebrate forelimb originating from a common ancestor is plausible
-homologous structures: structures with similar structural elements and origin but may have different functions
Analogous structures: body parts that perform similar functions, not evolved from the same ancestors
- structural composition is normally very different
- Evidence from Embryology
study of early pre-birth stages of the development of an organism
- it can be used to determine evolutionary relationships between animals
- the embryos of different organisms exhibit similar stages of embryonic development
Evidence from DNA
- evolutionary relationships between species can be found in DNA since it carries genetic information
- 2 species have similar patterns in the DNA which can indicate they are from the same ancestors
Adaptations
make organisms ideal for their habitat
- structural behavior or physiological process that helps an organism survive and reproduce in a particular environment
Examples of Adaptations
Hibernation: physiological adaptation
- allows organisms to survive harsh climates
Migration: behavioural adaptation
- seasonal or annual migration changes the habitat of animals
- maximizes breeding and feeding potential
Camouflage: structural adaptation
Variation
structural, functional, or physiological differences between individuals
- not all variations become adaptations
–> determined by environmental factors for it to be positive, negative, or no effect
Explain how mutations might lead to genetic variation
mutations: changes in genetic material of an organism
- mutations such as ultraviolet radiation, are environmental agents that can also cause mutations in DNA
Selective advantage
- genetic advantage of one organism over its competitors
- over time it causes the organisms to be favoured in survival and reproduction in changing environmental conditions
natural selection?
the process that results when the characteristics of a population of organisms change over many generations
- very situational: some times can have no impact but others can help individuals survive and reproduce
selective pressure?
abiotic environmental conditions select for certain characteristics while. it selects against others
fitness
the contribution an individual makes to the gene pool of the next generation by producing offspring that survive long enough to reproduce
high fitness = surviving and reproduce
low fitness = low/no viable offspring
sexual selection
natural selection for mating based on competition between males or through displays and choices made by females
types of natural selection
- stabilizing selection
- favours an intermediate phenotype
- acts againsed extreme varients of the phenotype
- most common phenotype is made more common in the population
- extreme forms of the phenotype are removed
- occurs when environment conditions are constant
2.Directional Selection
- favours phentypes at one extreme
- common during times of envionrmental change
- when a population migrates to a new habitat that have differnet enviornmental conditions
- Distributive selection
- also called diversifying selection
- when extremes of range of phenotypes are favoured over intermediate ones
- intermediate phenotypes cna be eliminated from the population
artificial selection
- selective pressure exerted by humans on populations in over to improve or modify particular desirable traits
- eg: selective breeding
natural selection: due to enviornment
artificial selection: due to humans
what are some consequences of artificial selection?
- genetic engineering introduces new genetic information into domesticated organisms
- reduces genetic diversity because the main goal of domesticating organisms is to produce similar ones
- artificially selected crops normally have increased nutritional value and less pests
- plants bred to grow cannot tolerate bad soil conditions
- in animals it can cause problems in respiratory system
allele frequencies
the number of copies of an allele compared to the total number of alleles in a population
factors that change allele frequencies in population
5 factors that lead to evolutionary changes
- mutation
- gene flow
- non-random mating
- genetic drift
- natural selection
mutations
- mutation randomly introduces new alleles into a population
- change in DNA of an individual
- can effect the entire gene pool
- ## the greater diversity, the greater chance for selective advantage for some individuals
gene flow
- occurs between 2 different interbreeding populations that have different allele frequencies
- it is the net movement of alleles from one population to another as a result of migration of individuals
- population A to population B
non-random mating
- interbreeding
- when closely related indivudals breed together
- homozygous genotype frequencies are increased since close relatives share similar genotypes
- can lead to harmful recessive alleles being expressed (deformities and health problems)
genetic drift
- random change in genetic variation from generation to generation due to chance
- the smaller the population, the less likely the parent gene pool will be reflected in the next generation compared to a larger population
2 situations that lead to significant genetic drift
- the founder effect
- a change in gene pool that occurs when a few individuals start a new isolated population
- few individuals form a new population - population bottleneck
- change in gene distribution that results from a decrease in population size
- (starvation, disease, human activities, natural disasters)
- survivors only have a fraction of alleles before so the gene pool will loose diversity quickly.
speciation
formation of new species from existing species
- when new species are formed and seen it is called macroevolution
- when members of a sexually producing population can change so much that they can no longer produce viable offspring with original population
pre-zygotic isolating mechanisms
- impedes mating between species or prevent fertilization of the eggs if individuals from different species attempt to mate
5 types:
(prevention of mating)
1. behavioural isolating mechanisms - any special signals or behaviours specific to the species that prevent interbreeding
(songs of birds)
- Habitat Isolating Methods
- 2 species living in the same region but different habitats so they don’t encounter each other - temporal isolating mechanism
- same habitat but different mating or flowering times
(different times of day/seasons/years)
(prevention of fertilization)
4. mechanical isolating mechanisms
- anatomically incompatible (fail to fertilize)
- different species genitals will not fit together
- gametic isolating mechanisms
- the sperm in one species will not fertilize
- rarely form a zygote
post-zygotic isolating mechanisms
rare occasions when the two species can successfully fertilize –> there are barriers that prevent the hybrid zygotes from developing into a viable and fertile offspring
- 3 types:
1. hybrid inviability: - genetic incompatibility of the species maybe stop developing the hybrid zygote
- prevents normal mitosis
- hybrid sterility (infertility)
- two species can sometimes mate and produce hybrid offspring
- offspring cannot further reproduce after that - hybrid breakdown (morality)
- sometimes the first generation of hybrids are fertile but not of the second generation
types of speciation
- sympatric speciation
- speciation in which populations within the same areas diverge and become reproductively isolated - allopatric speciation
- population is split into 2 or more isolated groups by a geographical barrier - adaptive radiation
- the diversification of a common ancestral species into a variety of differently adapted species - divergent evolution
- species that were once similar to an ancestral species diverge or become extremely different - convergent evolution
- similar traits arise because different species have independently adapted to similar environmental conditions
