humans and the environ 2 Flashcards
arch lec 4,5,6
what is evolution?
Evolution – change in the heritable characteristics of biological populations over successive generations and relies on the process of natural selection.
two main scales of evolution
macroevolution
microevolution
Darwin’s theory of evolution key points
overproduction variation event - that changes environ selection adaptation passing on of genes
what is natural selection?
The successful traits will spread through the population.
This change in the frequency of specific traits in the population underlies evolution
what are the pro’s of population variation?
Some of these variations (traits) will allow the organisms possessing them to survive and reproduce better than those without these particular traits.
What controls the observable traits (phenotype)?
the genotype (genes)
what is a gene?
gene is a segment of DNA containing the code which instructs cells to produce a certain protein, which in turn determine a certain trait.
how many chromosomes in a human cell?
Every human cell contains 23 pairs of chromosomes, for a total of 46 chromosomes
what are some ‘abnormal’ traits caused by?
Some traits are caused by abnormal genes that are inherited or that are the result of a new mutation.
what is an allele
one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.
dominant alleles
will be expressed in the phenotype
how do populations generally remain constant in size?
Despite this high potential fertility, natural populations usually remain constant in size, except for small fluctuations.
Not all of the potential offspring survive. - natural selections selects against certain individuals with unfav traits
what happens If there are not enough resources for all of the individuals?
there will be competition for those resources.
Survivors represent a small part of the individuals produced each generation.
what does it mean to say that variation is heritable
Some of the variation in traits between individuals in the population is heritable
.
Heritable traits can be passed down from one generation to the next.
what does it mean when a species adapts to a new environment?
The favoured traits have spread through the population.
Over time, these changes can lead to the formation of a new species.
what does environmental pressure cause?
special adaptations
A trait may be favored due to enhanced survival or reproduction when faced with a particular aspect of the environment.
what happens when species moves to new environ or current environ changes?:
species adapts to new environment
sometimes results in a new species
what is evolution measured as?
measured as changes in relative proportions of heritable traits in a population over several generations.
do individual evolves?
no, only populations evolve
does natural selection work on heritable or acquired traits?
heritable
what are acquired traits?
Acquired traits (developed through life, like knowledge, ideas, skills etc) are not heritable and are not subject to natural selection.
what are beneficial traits?
A trait that is beneficial in one place or time may be detrimental in another place or time.
traits that aid the survival of a species
is natural selection random?
No. It occurs in response to environmental pressures and results in adaptation.
Reproductive success:
What happens during reproductive success?
Their alleles are being passed to the next generation in frequencies that are different from the current generation.
ways other than natural selection that allele frequencies can change from one generation to the next.
genetic drift - random loss of alleles
mutation - new mutation can add alleles
nonrandom mating - inbreeding increases that number of homozygous traits
migration - gene flow, shuffles genes between populations, can prevent speciation
explain genetic drift
Variation in the relative frequency of different alleles in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce.
what is the bottleneck effect? explain
Sometimes a catastrophic event can severely reduce the size of a population.
The random assortment of survivors may have different allele frequencies.
This is a type of genetic drift called the bottleneck effect.
what is the founder effect? Explain
when a small group of individuals becomes separated from the main population and form a new population (e.g. Islands). The allele frequencies in their gene pool may be different than the original population.
