Based on the objective you should feel comfortable calculating expected genotype frequencies when given observed allele frequencies. You should also be able to compare expected genotype frequencies from HWE to observed frequencies and determine if evolution is occurring. Here's a sample problem. You can do this without a calculator!Let's take the noob gene, a gene with two known alleles that determines feather color in the eastern lark. The two alleles, let's call them delta and gamma, can be sequenced. In fact, looking at a population in southern GA, you discover that 60% of the alleles in the population are the delta allele.1. What is the percentage of the gamma allele in the population?2. Even more interesting, based on HWE what is the expected frequency of the population that is homozygous gamma? 3. Now, after surveying an isolated population of eastern larks, you find that 20% of the population is homozygous gama (gamma gamma), 65% heterozygous (gamma delta) and 10% homozygous delta (delta delta) and 5% of the population is a previously undescribed genotype - zeta zeta (homozygous zeta). What can you conclude about evolution in the population and why? If evolution is occurring, which mechanism(s) would be responsible?

Answer and Explanation:

60% of the alleles in the population are the delta allele

1. What is the percentage of the gamma allele in the population?

According to Hardy-Weinberg, the allelic frequencies in a locus are represented as p and q, referring to the allelic dominant or recessive forms. The genotypic frequencies after one generation are p² (Homozygous dominant), 2pq (Heterozygous), q² (Homozygous recessive). Populations in H-W equilibrium will get the same allelic frequencies generation after generation. The sum of these allelic frequencies equals 1, this is p + q = 1.

In the same way, the sum of genotypic frequencies equals 1, this is

p² + 2pq + q² = 1

Being

According to the sum of the allelic frequencies

p + q = 1

1 equals 100%

100% 1

60%0.6

40%0.4

The percentage of gamma allele in the population is 40%.

2. what is the expected frequency of the population that is homozygous gamma?

The genotypic frequencies, F, after one generation are p² (Homozygous dominant), 2pq (Heterozygous), q² (Homozygous recessive).

F(gamma)= p²= 0.4²=0.16 =16%

F(delta)= q²= 0.6²=0.36 = 36%

F (gamma-delta) = 2xp2q= 2 x 0.4 x 0.6 = 0.48 = 48%

3.  20% of the population is homozygous gama (gamma gamma), 65% heterozygous (gamma delta) and 10% homozygous delta (delta delta) and 5% of the population is a previously undescribed genotype - zeta zeta (homozygous zeta). What can you conclude about evolution in the population and why? If evolution is occurring, which mechanism(s) would be responsible?      

20% gamma-gamma

10% delta-delta    

65% gamma-delta  

5% zeta-zeta  

This population has different genotypic frequencies with respect to the population in southern GA:

The gamma genotypic frequency is a little bit higher in the isolated population (16% vs 20%)

The delta genotypic frequency is considerably lower in the isolated population (36% vs 10%)

The heterozygotic genotypic frequency is also higher in the isolated population (18% vs 64%)

It appeared a new phenotype in the isolated population, probably due to a mutation in one of the genes. We can assume that this is a new mutation because its frequency is still low (5%).

Maybe, the mutation occurred in an individual of the isolated population, and with time, this mutation increased its frequency, up to a point of being phenotypically visible. This could be a case of a bottleneck example.

The founder effect is a special case of genetic drift, where a few organisms of one population settles down in a new area carrying the genes of the original population.  

Genetic drift is the random change in the allelic frequency in a population, from one generation to the other. The magnitude of this change is inversely related to the size of the original population. These changes produced by genetic drift accumulate in time, and eventually, some alleles get lost, while some other might get set.      

Founder effect refers to the consequences that occur from the origin of a new population that derives from a small number of founder individuals that come from an ancestral bigger population. This small group shows poor genetic variation and a high possibility of expressing a peculiar allelic composition. Some mutation might occur and it can accumulate in time.

enzyme speed up the reactions