Species members have different gene-allele combinations and so have different trait combinations {variation, species}|.
causes
Mutations or allele recombinations cause genetic variation. Sex increases variation by increasing gene combination.
causes: selection
Evolution typically changes population allele ratios. Climate changes increase variation by increasing environment variety. Isolation increases variation by increasing environment variety.
amount
On average, 6% of vertebrate genes vary from wild type. On average, 15% of plant and invertebrate genes vary from wild type.
effects
Most changes are not adaptive. Species with greater genetic variation evolve faster, because they can use more environmental niches.
effects: duplication
Gene duplication and body part duplication allow duplicates to perform new functions, while originals perform old functions.
effects: whole body
Isolated changes can happen, but, to be adaptive, changes must work together with whole body, which then evolves in response to changes. For example, brain and body evolved together. Finger muscles, bone, nerves, blood supply, and brain motor-and-sensory finger regions evolved together, because dexterity required linked development.
Populations have gene-frequency changes {microevolution}. Microevolution includes gene flow, mutation pressure, and segregation distortion.
natural selection
Natural selection causes most gene-frequency changes. Natural selection can cause adaptations in constant environments or make new genes in fluctuating environments. Natural selection typically stabilizes gene frequencies and decreases homozygote percentage. New species arise from microevolutionary changes by accumulated changes in one direction {progressive evolution}.
drift
Random gene-splicing errors can cause heterozygosity loss by genetic drift, but this factor only affects small populations with inbreeding and consanguinity.
Allele mutations can negatively affect other alleles {canalizing}.
Immigrations into populations {gene flow} have major and fast gene-frequency effects, mainly through hybridization.
Strain combinations {hybrid}| generally show the good results of outbreeding {hybrid vigor}.
Bluish pigmented areas {Mongolian spot} {Mongol spot} {blue spot}, near spine bases, are present at birth in some Asian, south European, American Indian, and black infants and typically disappears during childhood.
Minor gene-frequency-change factors {mutation pressure} include differing allele-mutation rates.
Minor gene-frequency-change factors {segregation distortion} {meiotic drive} include unequal allele production by heterozygous parents.
Males typically have larger size and different shape than females {sexual dimorphism}|.
Trait presence depends on making trait {proximate factor} and keeping trait during reproduction. Trait survival in species members depends on environment, reproduction accuracy, and protection from change {ultimate factor}.
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Date Modified: 2022.0225