17- selection+evolution Flashcards
genetic variation caused by
- mutations: changes to genes+chromosomes that may be passed on
- meiosis: new combinations of alleles in gametes formed
- random fertilisation: produces new allele combs in sexual reproduction
- random mating
polygene:
diff genes at diff loci all contributing to a particular aspect of phenotype
genetic diversity + how it leads to variation
total number of DIFF ALLELES in pop
diff combinations of alleles result in diff PROTEINS being produced->diff CHARACTERISTICS
allele
different version of a gene
prezygotic reproductive barrier
prevents fertilisation+formation of zygote
acts before fertilisation of egg
postzygotic reproductive barrier
produces as result of hybridisation(diff species), reduces viability/reproductive potential of offspring
sympatric speciation
(less frequent in animals)
ecological/behavioural separation leads to groups becoming reproductively separated with no gene flow between->forms separate species
why is genetic diversity important for a population, and why is lack of genetic diversity in small populations dangerous
genetic diversity->variation within population = essential in process on natural selection, allowing population to adapt to changes over time
small pops can’t adapt to change as easily+more likely to become extinct
genetic drift
change in allele frequency due to chance- not natural selection
likely when small number population separated from rest of large pop
genetic drift leads to
loss of genetic variation- certain alleles lost due to chance
founder effect
extreme genetic drift where small populations arise due to establishment of new colonies by few ISOLATED individuals
founder effect leads to
smaller gene pools+less gen diversity within population
rare alleles in OG pop have higher frequency
bottleneck effect
large reduction in pop size lasting at least 1 gen
greatly reduces gene pool+diversity
conditions for Hardy Weinburg
no mutations,
pop isolated,
no selection,
large pop,
mating within population is random
Which factors contribute to the emergence of new species
reproductive isolation of populations
genetic divergence driven by natural selection
genetic drift
t-test measuring variation
comparing means of 2 sets of data
Follow normal distribution, continuous data,
Equal variance/SDs
Samples independent of each other
environmental factors limiting populations
Competition for food
Competition for mates
Supply of water
temp
types of selection
directional
stabilising
disruptive
directional selection
Increases for one extreme, normal shifts in direction of favoured extreme
stabilising selection
Increases allele frequency for the average phenotype, decreases allele frequency for extremes, curve narrows
disruptive selection
Increases for multiple extremes, decreases for intermediates
Curve shifts into M shape, 2 peaks either side of OG peak
Processes causing allele change
Natural selection
Founder effect
genetic drift
bottleneck effect
natural selection
Selection pressures result in gradual change in allele frequency over several generations
founder effect
Changes in allele frequencies occur in diff direction for newly isolated small pop in comparison to larger pop- due to CHANCE
genetic drift
Gradual change in allele frequencies in small pop due to chance, not natural selection
bottleneck effect
Reduction in gene pool of pop due to dramatic decrease in pop size
artificial selection
- Select a population that displays variation.
- Select individuals with desired traits, (high milk production)
- Selectively breed individuals together that display desired traits.
- Grow and test the offspring for the desired traits.
- Repeat the selection process across many generations
Evolution
formation of new species from pre-existing species OVER TIME
variation: Change of characteristics of species due to allele frequency changes
natural selection / selective advantage for survival / survival of the fittest
Speciation
organisms w/ same features, interbreed to produce fertile offspring, reproductively isolated from other species
morphological
structural features
physiological
metabolic processes in living organisms
biochemical
base sequence in DNA molecules + a.a. Sequences
Molecular comparisons between species
- compare a.a. sequences of proteins. more sim sequence=more closely related
- Nucleotide sequences of mtDNA
Characteristics of mtDNA
- Circular, doesn’t cross over
- Mutations occur at constant rate- molecular clock
- mtDNA mutates faster than nuclear DNA- changes only arise through mutation, aren’t repaired. Not associated with histones.
- Smaller, fewer genes->quicker mtDNA analysis
- mtDNA passed from mother to offspring, all descendants of 1 female have identical mtDNA
explain how variation in ecosystems contributes to biodiversity
- diff habitats
- diff niches
- diff selection pressures
- genetic diversity
- adaptation
- diff climates
