Natural selection

Question 1

What is Natural Selection?

Answer 1

Better adapted individuals survive longer and mate more frequently so leave more offspring

Question 2

Continuous variation

Answer 2

type of genetic variation in which individuals in a population show a range of intermediate phenotypes for a particular trait, rather than clustering around distinct, discrete categories e.g. height

Question 3

Discrete variation

Answer 3

type of genetic variation in which individuals in a population fall into distinct, non-overlapping categories for a particular trait e.g. blood group

Question 4

The basis for natural selection

Answer 4

Variation

Heritability - individuals inherit characteristics from their parents, variation has a deterministic genetic basis
-Mendelian inheritance - no change in gene frequency

Competition and fitness - finite amount of resources available to members of a species, some individuals successful, some not. Not all individuals in a population survive to reproduce
-Competition consequence of limited amounts of resources
-Fitness - measure of the reproductive success of an individual
—–If individuals pass copies of 100% of genes, fitness = 1.0

Question 5

Types of selection

Answer 5

Selection occurs when genotypes differ in their ability to pass genes on to the next generation
-Genotype successful = gene frequency increase
-Genotype unsuccessful = gene frequency decrease

Natural selection - the differential survival and reproduction of individuals due to differences in phenotype
-Directional selection
—–Leads to long-term evolutionary trends in the evolution of traits
—–Shift in the mean population phenotype
-Stabilising selection
—–Leads to reduction in the range of trait values
—–Selects against extreme trait values(extreme phenotypes disfavoured)
-Disruptive selection
—–Leads to multi-modal distributions of traits
—–Favours both extremes of the population (mean phenotypes selected against)