lecture 2 Evolution: Species and Adaptations Flashcards
6how does Evolution by Natural Selection occur?
1.Individual variations within a population -morphology, physiology, behaviour
2.Variation is heritable
3.Some forms are more successful at surviving and reproducingthan other in a given environment
Differential reproductive success based on the traits of the organism
what is the definition of evolutions, alleles, populations and mutations??
-Change in the frequency of alleles in a population over time
-A variant of a gene or trait
-A localized group of organisms which belong to the same species
-Mutations : change in the sequence of an organism’s DNA
what is the founder effect?
*Founder effect: Few individuals start a new population with a different allele frequency than the original.
define gene flow?
Gene flow, also known as gene migration or allele flow, is the transfer of genetic material (alleles) between separate populations. This process occurs when individuals from one population migrate to another and interbreed, introducing new alleles into the gene pool of the recipient population. Gene flow is an important mechanism of evolution as it can affect the genetic diversity and the evolutionary trajectory of populations.
what is evolution by genetic drift?
Evolution by genetic drift is a process through which allele frequencies within a population change over time due to random sampling effects. Unlike natural selection, which involves differential survival and reproduction based on traits, genetic drift is driven by chance events that influence which individuals reproduce and pass on their genes
what are the different ways in which evolution can occur?
-Mutations
*Sexual reproduction
*Genetic drift
-Founder effect
-Gene flow
define species
(Biological def.) individuals with the potential to interbreed and produce fertile offspring in nature
define population
A localized group of organisms which belong to the same species
what is the problem with the species definition?
-Difficult to apply to fossils
-Asexual organisms don’t fit the criteria
-Horizontal gene transfer
why is appearance not everything for species?
Western and Eastern meadowlark: *appear identical
*their ranges overlap
*distinct songs prevent interbreeding
Other birds (fairy wrens; north cardinals) show a drastic sexual dimorphism but they are the same species
what is speciation?
lineage-splitting event that produces two or more separate species
Geographic isolation -Allopatric speciation (allo-‘other’+ patra ‘fatherland)
*probably most vertebrates
*species occupy areas separated by time or space
what is allopatric speciation?
Allopatric speciation is a process through which new species arise due to the geographic separation of populations. This type of speciation occurs when a population is divided into two or more isolated groups by physical barriers such as mountains, rivers, or distance, preventing gene flow between them. Over time, these isolated populations evolve independently through mechanisms like mutation, natural selection, and genetic drift.
what is sympatric speciation?
Sympatric speciation (Sym‘together’+ patra‘ fatherland)
*especially plants and insects
*species occupy the same place at the same time
Apple maggot flies: Gene flow has been reduced between flies feeding on different food
Sympatric speciation is a process through which new species arise from a single ancestral species while inhabiting the same geographic region. Unlike allopatric speciation, where geographic isolation is key, sympatric speciation occurs without physical barriers to gene flow. Instead, it involves reproductive isolation due to genetic, behavioral, ecological, or other factors.
what is Sympatric speciation by polyploid
Sympatric speciation by polyploidy is a specific mechanism of sympatric speciation in which new species arise due to changes in chromosome number within a single population, without geographic isolation. Polyploidy occurs when an organism has more than two complete sets of chromosomes, and it can lead to reproductive isolation and the formation of new species.
Polyploidy Event: Polyploidy can occur through various mechanisms, such as errors during cell division (e.g., nondisjunction), hybridization between closely related species, or whole genome duplication. These events result in individuals with more than two complete sets of chromosomes (triploid, tetraploid, etc.).
Reproductive Isolation: Polyploid individuals often experience reproductive isolation from their diploid counterparts due to differences in chromosome number. When diploid and polyploid individuals mate, their offspring, known as triploid hybrids, are often sterile due to difficulties in meiosis and chromosome pairing. This sterility acts as a reproductive barrier, preventing gene flow between diploid and polyploid individuals.
Polyploid Establishment: Despite the initial sterility of triploid hybrids, some polyploid individuals may undergo self-fertilization or mate with other polyploids to produce fertile offspring with the same chromosome number. This establishes a new, reproductively isolated lineage within the same geographic region as the diploid population.
Genetic Divergence: Over time, the polyploid population accumulates genetic differences from the diploid population due to factors such as natural selection, genetic drift, and mutation. These genetic differences can lead to adaptations to specific ecological niches or habitats, further reinforcing reproductive isolation.
Speciation: Eventually, the genetic divergence between the diploid and polyploid populations becomes significant enough to classify them as separate species. They are reproductively isolated due to differences in chromosome number, and they may also exhibit ecological or behavioral differences that contribute to their distinctiveness.
Sympatric speciation by polyploidy is particularly common in plants, where it can occur rapidly and lead to the formation of diverse species within the same habitat. It provides a mechanism for speciation without the need for geographic isolation and underscores the importance of chromosomal changes in driving evolutionary processes.
what are ring species?
Population of a single species encircle an area of unsuitable habitat
*At the end, the populations have expanded so far that the ends cannot mate
*Salamander Ensatinaeschscholtziiin California
