Lesson Four Flashcards
who developed the theory of evolution by natural selection?
Charles darwin
what does fitness mean in natural selection?
defined as the relative genetic contribution of individuals for future generations
what are adaptations?
an evolutionary process that changes anatomy, physiology or behaviour resulting in a populations increased ability to live in that particular environment
what is phenotypic variation?
occurs when the expression of a gene is changed in response to the environment (combined effects of genes and environment
What is a phenotype?
a set of observable characteristics of an individual
what is phenotypic plasticity?
this is when an organism has the ability to change their phenotype without altering their genes, this is in response to the environment
what is trai evolution?
the process by which the characteristics of a species change over time due to DNA mutations, this is on a short time scale
what is evolutionary change?
the process by which organisms heritable traits change over generations allowing them to better adapt to their environment
what does evolution by natural selection depend on?
the heritability of traits
what can cause some sources of genetic variability?
mutations in the genome, new alleles forming, chromosome break repairs may invert a fragment reversing the fragments gene sequence and changing expression.
what does the Hardy-Weinberg principle state?
In a population at random in the absence of evolutionary forces, allele frequencies will remain constant. variations in allele frequencies over time leads to microevolution
what causes macroevolution?
natural selection and random processes such as genetic drift if accumulated can lead to genetic divergence leading to speciation aka macroevolution
what is stabilizing selection?
Stabilizing selections tends to favour the average phenotype. (largest/smallest individuals have the lower rate of survival/reproduction) The population tends to sustain the same average phenotype over time, decreasing the frequency of extreme phenotypes. They may be challenged by environmental causing directional change. A population matched well to the environment may maintain stable traits.
what is directional selection?
Directional selection favours an extreme phenotype over the average. As a consequence differences in survival and reproduction alter the average phenotype (most phenotypes have a lower reproductive and survival compared to the exceptional phenotypes). This selection occurs when an individual has an extreme advantage over others. Several extremes may have advantaged leading to a more diversified population
what is disruptive selection?
disruptive selection favours two or more extreme phenotypes over the average. change depends on genetic influence over the phenotype. The rate of evolution due to natural selection may vary. some selective pressure require rapid evolution, others are more subtle.
what is genetic drift?
it is a change in the frequency of an existing gene variant in a population due to a random chance. (with a finite number of individuals producing a finite number of offsprings, gene frequency will change)
what is one dominant factor influencing the rate of evolution?
population size, with drift causing a more rapid evolutionary change in smaller populations. Loss of genetic variation (particularly rare alleles), through drift is a significant concern for small populations such as endangered species and isolated habitats
what is the founder effect?
a decrease in genetic diversity associated with the formation of a new small population.
what is speciation?
physical/ecological processes interact with selection and drift to produce a new species
morphological species concept
a classification of organisms belonging to the same species based on conserved morphological (anatomical) features. This concept may be useful when organisms do reproduce sexually or are extinct.
biological species concept
where populations of organisms able to interbreed and produce viable, fertile offsprings are classified as belonging to the same biological species
what is ecoline, or cline?
gradual change in a genotype/phenotype of a species over a large geographical region. individuals of a species on opposite ends may appear quite different from each other with no specific location at which individuals “became” different
what is reproductive isolation?
a set of barriers that prevent different species from breeding and producing healthy offspring’s. (this is a critical requirement of species is reproductive isolation between populations)
What is prezygotic isolating mechanisms?
this is a part of reproductive isolation, and this prevents two individuals from forming a zygote
what is postzygotic isolating mechanisms?
This is a part of reproductive isolation and occurs after the zygote has been formed
ecological isolation
two individuals physically separated such that they are unable to encounter each other (Prezygotic)
Temporal isolation
individuals are fertile at different times (prezygotic)
behavioural isolation
many animals require specific behaviours by one or both partners prior to mating. even if both are fertile and in the same location, they may not mate if the proper behavioral cues have not been received by one or both individuals (prezygotic)
Mechanical isolation
(Physical intimacy) two individuals have genitalia that simply do not fit together, inability to penetrate/.deliver sperm or use of different pollinators (prezygotic)
Hybrid inviability
results if zygotic development is abnormal and the developing hybrid dies prior to sexual maturity (postzygotic)
hybrid sterility
occurs if the hybrid develops normally but is unable to produce viable gametes (postzygotic)
what are the three causes of speciation?
allopatric (geographic) - single groups spatially subdivided. Parapatric - population expands into a new habitat within the pre existing range of the parent species. Sympatric - single parent population forms genetically distinct subpopulations by natural selection without isolation.
Sympatric speciation
Sympatric speciation is that a disruptive selection for a trait causes groups of individuals, even within a single population to differ greatly in phenotype. Usually accompanied by assortative mating genetic differences can occur. evolving into reproductive isolation
what is assortative mating?
individuals choose mates similar to themself (positive assortative mating) or mates that are different (negative assortative mating) Positive assortative mating is likely to cause sympatric mating
what is parallel evolution?
sometimes different isolated species in similar habitats evolve similar traits. this is called parallel evolution. similar environmental pressures leads to the selection of similar traits.
