Question

A new mutation arises in a population of size 10,000 diploid individuals and then quickly increases to a frequency of 20% in the population. The mutation then stays at frequency 20% for 1,000 generations before becoming lost. Describe one scenario of finesses that could give rise to these trajectories. Note, you are allowed to have fitness change over time.

Answer 1

Suppose in a area, there is population of 1000 white flower tree. They are pollinated only through air because insects are not attracted with their white petal colour. The white colour of petal is due to a pigment (protein). Now, after a mutation in the white pigment producing allele, the allele is transformed into a red pigment producing allele. The tree with red flower (air + insect pollination) will have more fitness in comparison to the tree with white flower (only air pollination). So, the frequency of the red pigment producing allele gradually increases as they are selected by nature more frequently.

Now, the insects are eliminated due to environmental pollution. So, the red allele don't get any extra advantage. So, the frequency of red allele will decrease gradually.