Download Variation One of Darwin`s biggest observations was that individuals

One of Darwin’s biggest observations was that individuals in a population are varied.
This means that they are unique and have different physical and behavioral
characteristics that make them different from each other.
Variation: the differences among parents and offspring in a population
Adaptation- traits or characteristics that
enhance survival. The need to be inheritable in
order to considered a species adaptation
Causes
Gene mutations

Migration- new alleles enter a population

Interbreeding- alleles are emphasized in
a population, increase in recessive phenotype
appearance

Recombination of chromosomes during
crossing-over in meiosis
Mimicry-to copy the appearance of another
Camouflage- to blend in
The process of become two distinct species from one original species
Species- a group of organisms that can interbreed
Reasons/causes of speciation:
Reproductive Isolation: the members of two populations cannot produce fertile
offspring
Behavioral Isolation: different mating rituals such as mating dances or coloration
Temporal Isolation: reproduction takes place at different times (day vs. night, spring
vs. fall)
Geographic Isolation: populations are physically separated by a land mass or water
feature and therefore do not interact
Gene Pool: all the genes present in a population
Relative frequency: the number of times an allele shows up in a population
Genetic Drift-random change in the allele frequency of a
population. This affects small populations the most. It can be
due to mutation, death, migration, or any other RANDOM
occurrence. Genetic drift is not predictable and not necessarily
toward the overall fitness of the population.
Bottleneck Effect- change in the allele frequency in which
A diverse large population undergoes a catastrophic
reduction in numbers due to natural hazards, disease
etc. Only the survivors alleles can then be passed on
to the next generation, creating a much smaller gene
pool and dramatic relative frequency of allele
changes
Founder EffectLarge decrease in gene pool due to an isolated
colony being formed. Recessive traits get a higher
relative frequency.
Types of Selection
Directional Selection: The original “average “ of a
Particular trait within a population is shifter to favor
one end of the spectrum.
Example: when only large seeds are available
the birds with larger beaks are more successful so
the allele for larger beaks is selected and the
populations allele frequencies shift to have higher
occurance of the favored allele.
Stabilizing Selection:
the individual with the
“average” version of the trait has the greatest
Fitness. Those at the ends of the spectrum are
less fit and therefore are less likely to survive to
reproduce. The allele frequency of the “average”
increases.
Example: in dandelions the smallest do not
survive due to lack of nutrients and the largest are
at greatest risk of parasitism.
Disruptive Selection:
The individuals with the
Extreme version of the trait are most fit and will
have greater ability to survive and reproduce and
therefore pass on their traits. The “average”
individual will be less likely to pass on the trait.
Example: in a particular butterfly population
The drabbest coloration mimics an unpalatable (gross tasting) species and is
therefore not eaten. The boldest colored mimics another unpalatable species and is
therefore not eaten, those that are in the middle of the spectrum do not mimic
another species and are therefore eaten and die.