Question

(a) What is the difference between absolute fitness and relative fitness of an organism? [5 marks]

(b) Co-dominance is a type of non-Mendelian inheritance pattern that finds the traits expressed by the alleles to be equal in the phenotype. Give an example of a phenotype that is caused by co-dominant alleles in humans [5 marks]

(c) Coat colour in various animals is associated with their ability to hide from predator attacks. Animals with coat colours that match their environments more closely are more likely to survive than those with darker or lighter coats. What type of selection is this an example of? [5 marks] (d) In rural areas, peppered moths are almost all a very light colour. However, the same species of moths have a very dark in colour in industrial areas and very few mediumcoloured moths are seen in either location. What type of selection is this an example of?[5 marks]

Answer 1

a) Absolute fitness-  

The absolute fitness (W) of a genotype is defined as the proportional change in the abundance of that genotype over one generation attributable to selection.

For example, if n(t)n(t) is the abundance of a genotype in generation t in an infinitely large population, and neglecting the change in genotype abundances due to mutations, then for n(t+1)=Wn(t)n(t+1)=Wn(t). An absolute fitness larger than 1 indicates growth in that genotype's abundance; an absolute fitness smaller than 1 indicates decline.

Relative fitness

Whereas absolute fitness determines changes in genotype abundance, relative fitness (w) determines changes in genotype frequency.

If N(t) is the total population size in generation t, and the relevant genotype's frequency is p(t)=n(t)/N(t)p(t)=n(t)/N(t).

Relative fitnesses only indicate the change in prevalence of different genotypes relative to each other, and so only their values relative to each other are important; relative fitnesses can be any nonnegative number, including 0. It is often convenient to choose one genotype as a reference and set its relative fitness to 1. Relative fitness is used in the standard Wright-Fisher and Moran models of population genetics.

b) When two alleles for a trait are equally expressed with neither being recessive or dominant, it creates codominance. Examples of codominance include a person with type AB blood, which means that both the A allele and the B allele are equally expressed.

c) Hidden nicely against its background, an animal can escape its enemies for another day. The particular colors on an animals are determined partly by the genes its gets from its parents. That means that genes that hide animals can spread thanks to natural selection, leading to the evolution of exquisite camouflage.

d) This is an example of gene variation.

For the moths in industrial areas, the dark colouration developed because they were trying to hide.

In rural areas many moths are brightly colored because they're toxic. As an extra layer of protection, some vivid moths mimic the look of toxic ones, even though they're not poisonous themselves.

Most moths fly at night and sleep during the day, so they don't need the bright colors of butterflies. The dull colors help a moth camouflage himself as he rests during the day, allowing him to blend in as he sits on a tree branch or among the brush.

A colour variation arises during reproduction, so that there is one moth that is very dark in colour instead of medium coloured. This moth, moreover, can pass the colour on to its progeny, so that all its progeny are dark.