4.3: Balancing Selection and Relative Fitness

balancing selection

a type of natural selection that maintains genetic diversity by favoring multiple alleles, allowing different traits to coexist in a population and prevents any single allele from becoming dominant

types of balancing selection

heterozygote advantage and negative frequency-dependent selection

negative frequency-dependent selection

the fitness of a phenotype or genotype decreases as its frequency in the population increases, essentially favoring rare variants and disfavoring common one

negative FDS example

lizards

• orange = aggressive and defends territory

• blue = less agg and little territory but guards females

• yellow = similar colour to females and sneak around

cycle between colours

• y common = b favoured = b increases

• b common = o’s aggression is advantage = o increases

• o common = y increases

heterozygote advantage

heterozygote individuals have a fitness advantage over homozygotes

relative fitness

describes the success of the most advantageous genotype in population relative to all other genotypes

• ranges from 0 to 1

example of heterozygote advantage

individuals with 1 sickle cell allele and 1 normal allele are more resistant to malaria than those with 2 normal alleles and not affected by severe sickle cell anemia like people with 2 sickle cell alleles

relative fitness vs fitness

relative = success of a genotype

fitness = success of an organism at surviving and reproducing