natural selection Flashcards
whats The basis for Natural Selection
-Better adapted individuals survive longer and mate more frequently so leave more offspring
-Poorly adapted individuals die sooner or fail to mate so leave fewer offspring
what are the 3 conditions necessary for selection
1) Variation- individuals vary in most traits
2) Heritability - variation is passed on via inheritance
3) Competition & fitness - individuals compete for limited resources
variation and how its involved with natural selection
-It is commonly observed that there is variation within a species – not all individuals are alike and there is even variation between parents and offspring
what are the different types of variation
-continuous
-discrete
-Biston betularia - discrete colour morphs- controlled by 1 or 2 genes
-Cepaea nemoralis – continuous range of variation in banding intensity- body and colour variation and body size can be controlled by many different genes
heritability and how its involved with natural selection
-Individuals inherit their characteristics from their parents
-The basis for this inheritance is genetic
-i.e. variation is not completely random, but has a deterministic genetic basis
does mendelian inheritance lead to evolution
- no because it doesnt change the gene frequency
-It does not produce a directional change in gene frequency
-P generation:
S= 0.5, s=0.5
-F1 generation :
S= 0.5, s=0.5
-F2 generation :
S= 0.5, s=0.5
how is competition and fitness involved with natural selection
-There is a finite amount of resource available to members of a species and this means that some individuals are successful and others are not
-Consequently not all individuals in a population are able to survive to reproduce
how is competition involved in natural selection
-Ecological competition is the consequence of limited amounts of resources
-Resources can include food, water, shelter, space or mates
-There is a direct relationship between amount of resource captured and fitness
how is fitness involved in natural selection
-Fitness: this is a measure of the reproductive success of an individual
-If an individuals pass on copies of 100% their genes to the next generation, on average, then fitness = 1.0
-Note though: to achieve fitness = 1.0, diploid organisms need to produce at least 2 offspring
natural selection with Biston betularia – peppered moth
-black- occurs widely natural state before industrial resistance
-white- after industrial resistance- blend in better, more successful by default
-black moths die because they get eaten
competition for mates
-Ecological competition is the consequence of limited amounts of resources
-Resources can include food, water, shelter, space or mates
-There is a direct relationship between amount of resource captured and fitness
whats sexual selection
fitness- survival
fitness- reproduction- fecundity( natural selection) and number of mates (sexual selection)
when does selection occur
-when genotypes differ in their ability to pass genes on to the next generation
-if a genotype is successful its genes will increase frequency
-if a genotype is unsuccessful its genes will decrease in frequency
types of natural selection
-Directional selection: Selection generates a long-term change in a trait, Directional selection leads to long-term evolutionary trends in the evolution of traits
-Stabilizing selection: Selection agains extreme trait values, Stabilizing selection leads to reduction in the range of trait values
-Disruptive selection: Selection for multiple optimum trait values, Disruptive selection leads to multi-modal distributions of traits
examples of stabilising selection
-e.g. Bicyclus anynana
-Eyespots provide defence against predators
-Selection against eyespots that are too large or small
