Ch. 16, 17, 18 Evolution Flashcards
how do we know evolution exist?
by studies in anatomy, embryology, molecular biology, and biogeography
how evolution leads to natural selection
- some traits of an individual are more adaptive to changing environment
- more offspring are produced with favorable genes so the resources, reproduction and survival are limited
Charles Darwin
along with Wallace, came to the idea of natural selection around 1858
- published a controversial “On the Origin of Species”
adaptation
a heritable trait that helps the survival and reproduction of an organism in its present environment
the basis of variation
genetic variation
types of genetic variation
- dimorphic
- polymorphic
dimorphic trait
traits with 2 distinct forms: white or purple flowers on pea plants
polymorphic trait
traits with more that 2 distinct forms: ABO blood type in humans
basis of genetic variation
mutation (change in DNA pattern)
mutation types
- neutral: no effect on survival or reproduction
- lethal: ends in death
- beneficial: gives slight advantage toward survival and reproduction
sources of mutations
- random genetic changes
- crossing over in Meiosis I
- independent assortment in Meiosis I
- fertilization
gene pool
sum of all genes in a population
allele frequency
rate at which a specific allele is present within a population
microevolution
change in allele frequency in gene pool
-always occurring in natural populations due to mutations and/or natural selection
macroevolution
large scale evolutionary pattern above the species level
-ex. land plants evolving from algae, extinction of dinosaurs
the two main evolution types
- divergent evolution
- convergent evolution
divergent evolution
changes in body or form from a common ancestor
ex. homologous structures (limbs of vertebrate animals)
- flight in birds and bats
- flippers in penguins and porpoises
homologous structures
structures in organisms that share the same basic form
- same genes direct their development
- may be used for different purposes
vestigial structures
structures that exist in organisms but seem to have no apparent function
- -appear to be residual parts from a past common ancestor–
- ex. appendix in humans, pelvis on snakes, goosebumps
convergent evolution
when traits evolve similarly in species that do not appear to have a common ancestor
-have analogous structures
due to similar selection pressures
-may perform the same function because of environment pressures
analogous structures
structures that look alike but evolved independently
transitional soforms
an intermediate form of an organism linking two other organisms together
patterns of natural selection
- directional selection
- stabilizing selection
- disruptive selection
directional selection
an extreme trait is more favorable
stabilizing selection
an intermediate trait is more favorable
disruptive selection
extremely different traits are more adaptive and favorable
natural selection and diversity
sexual dimorphism different looking male and females
- due to sexual selection: traits to better attract mates
females either choose mate(s) or males compete for a group of females
balanced polymorphism and the heterozygote
two or more alleles continue circulating at a relatively high frequency in a population
- arises in nature favoring the heterozygotes
ex. sickle cell anemia and malaria resistance
the level of genetic variance
- are best maintained with sexual reproduction as genetically different parents create diverse children
- best to avoid asexual reproduction which leads to clones
non-selective evolution (evolution by “chance”)
- genetic drift
- fixed allele
genetic drift
random chance in allele’s frequency over time, brought by chance alone
-by chance to be in the right place at right time or wrong place wrong time
type of genetic drifts
- bottleneck: results in large part of the population getting wiped out
- founder effect: small group establishes a new population
fixed allele
individuals for allele are all homozygous
-common among small populations
gene flow
movement of alleles between populations
-can result in change or stabilization of allele frequencies
speciation
evolutionary process in which new species form
- occurs when populations cross breed (not interbreed)
- increase the number of genetic variation/differences
- over time they become so different we call them different species
types of speciation
- allopatric speciation
- parapatric speciation
- sympatric speciation
allopatric speciation
arises from physical separation between populations
- reproductive isolation
- geographic isolation
reproductive isolation
biological/physical barrier gene flow
- influenced by how an organism reproduces
- can prevent interbreed–even if populations meet again
- -have pre-zygotic and post-zygotic factors
geographic isolation
physical geographical barriers to gene pool
*influenced by how species travel
hybrid
cross between 2 different species that are similar
sympatric speciation
populations inhabiting same regions with no physical barriers between them
- can occur in single generations when chromosome number multiplies
-also occurs with no number change
more common in plants
parapatric speciation
adjacent populations speciated despite being in contact across common borders
- divergences spurred by local pressures are reinforced
ex. velvet walking worm - hybrids that are formed in contact zone are not better fit
adaptive radiation
organisms that do not go extinct may go under adaptive radiation
- key innovation
- co-evolution
key innovation
new trait that allows one organism to exploit a habitat more effectively
co-evolution
two species evolve jointly because of close ecological connection
