Lecture 3: Natural Selection pt 2 Flashcards
Three ways natural selection works
- it can be directional
- It can be stabilizing
- It can be disruptive selection
direction selection
it favors smaller individuals and will if the character is inherited, produce a decrease in average body size
Stabilizing selection
example: the average members of the populaiton, with intermediate body sizes, have higher fitness than the extremes
disruptive selection
Both extremes are favoured relative to the intermediate. types
why disruptive
in an environment with a bimodal distribution of certain traits, can increase the genetic diversity of a population
No relation between fitness and the character
there is no natural selction
Variation in natural populations is widespread`
The extent of variation, particularly in fitness, matters for understanding of evolution
Variation
exsits in morphological, cellular, such as chromosomal, biochemical, such as in enzymes, and genetic character
Morphological Leve
at the morphological level the individuals of a natural population will be found to vary for almost any character we may measure
continuous variation
In some characters, like body size, every individual differs from every other individual (decimal points)
discrete variation
some morphological characters like sex or gender. some individuals of a population being female, others being male
Polymorphism
A population that contains more than one recognizable form is polymorphic. There can be any set of relative frequencies
Number of forms in the population increases
the polymorphic, categorial kind of variation blurs into the continuous kind of variation
Cellular level
variation can be found in cellular character such as the number and structure of the chromosomes
Inversion
banding pattern and the order of genes in a region of the chromosomes is inverted
