Question

Define what is meant by the statement “relative fitness of genotype aa” as related to population genetics.

Answer 1

Solution:-

The relative fitness (w) , as the term suggests, is the fitness expresses relate to survival rate and/or reproductive rate .

Survival rate

The percentage (%) of individuals born that survive to reproductive age.

Reproductive rate

The average number of offspring born per individual.

Relative fitness (of genotype)

It can be defined as the survival and or reproductive rate of a genotype relative to the maximum survival and or reproductive rate of among genotypes.

Calculation if Relative fitness

Consider three genotypes in a population such as, AA, Aa and aa.

1) First scenario

• The Survival rate differs and reproductive rate are all equal for this three genotypes.
• The relative fitness calculated by dividing each survival rate of genotypes by highest survival rate.

	AA	Aa	aa
Survival rate	20%	20%	40%
Reproductive rate	8	8	8
Relative fitness (w)	20/40= 0.5	20/40=0.5	40/40=1

2) Second scenario

• The Reproductive rates are different and Survival rates are same.'
• The relative fitness calculated by dividing each reproductive rate of genotypes by highest reproductive rate.

	AA	Aa	aa
Survival rate	20%	20%	20%
Reproductive rate	8	8	4
Relative fitness (w)	8/8= 1	8/8 = 1	4/8 = 0.5

3) Third scenario

• Both Reproductive and Survival rates are different

	AA	Aa	aa
Survival rate	20%	20%	30%
Reproductive rate	8	6	4
Survival rate x Reproductive rate	0.2x8=1.6	0.2x6=1.2	0.3x4=1.2
Relative fitness	1.6/1.6=1	1.2/1.6=0.75	1.2/1.6= 0.75

Interpretation of fitness

• Relative fitness (w) =1 means the genotype is the most fit, most successful of the three other genotypes in that particular environment and time.
• If the relative fitness of "AA" genotype waa=1 means, AA genotype is the most fit and successful genotype.
• The relative fitness of "aa" genotype waa=0.75 means "aa" genotype produce offspring on average at 75% of the rate of individuals with most successful genotype with relative fitness of w=1.