Q. 18 - Biology

Question

Imagine you are trying to test whether a population of flowers is undergoing evolution. You suspect there is selection pressure on the color of the flower: bees seem to cluster around the red flowers more often than the blue flowers. In a separate experiment, you discover blue flower color is dominant to red flower color. In a field, you count $600$ blue flowers and $200$ red flowers. What would you expect the genetic structure of the flowers to be? 

Step-by-Step Solution

Answer

Flowers have $200$ homozygous blue flowers, $400$ heterozygous blue flowers, and $200$ red flowers in their genetic structure.

Step 1 : Hardy- Weinberg principle :

The Hardy- Weinberg equilibrium, model, theory, or rule is also known as the Hardy- Weinberg principle. In the absence of evolutionary effects, the frequencies of alleles and genotypes in a population will, on average, remain constant from generation to generation.  

Step 2 : Explanation :

Hardy-Weinberg equation :  

$p^2+2pq+q^2=1$

where,

$p^2$ is frequency for homozygous genotype AA.

$q^2$ is frequency for homozygous genotype aa.

$2pq$ is frequency for heterozygous genotype Aa.

For all alleles at the locus, the overall allele frequencies must equal $1$.

For a population in equilibrium genetically: 

$$\begin{gathered} p+q=1.0 \\ q=0.5 \\ p=1-q=0.5 \end{gathered}$$

Red is recessive.

Hence, the total number of homozygous recessive is;

$q^2=\frac{200}{800}=0.25$

Total number of homozygous dominant.

$p^2=0.25$

Total number of heterozygous dominant.

$2pq=0.5$