10/10 Daily Catalyst. 1. Define allele frequency? 2. What causes evolution? 3. What is effected more by changes in allele frequencies?. 10/10 Daily Catalyst Answers. 1. Define allele frequency? How ofte n alleles appear in the population 2. What causes evolution?
FIVE Conditions of Hardy-Weinberg Equilibrium:
The population must be large.
Population must be isolated to prevent gene flow(No immigration or emigration).
No mutations occur.
Mating is completely random.
No natural selection (Every offspring has an equal chance of survival without regard to phenotypes).
Condition #4 can never be met. Mating is never random. Pollen from an apple tree in Ohio is more likely to pollinate a tree in Ohio than one in Washington state.
Condition #5 can never be met. There will always be variation. Variation can help organisms survive longer and/or reproduce more effectively.
Since 3 out of the 5 H-W conditions can never be met, evolution DOES occur and allele frequencies do indeed change.
Here we go with our frogs again! Let’s suppose that in a population of 100 frogs, 36 were green (CGCG), 48 were blue (CGCR) and 16 were red (CRCR) and there was total random mating.
Thus, it can be assumed that 60% of all the gametes (eggs and sperm) should carry the CG allele and 40% of the gametes should carry the CRallele.
A population Punnett square is shown above. It indicates that the next generation should have the following offspring distribution: 36% green (CGCG), 48% blue(CGCR), 16% red (CRCR). When the second generation gets ready to reproduce, the results will be the same as before.
So, the allele frequency remains at 0.40 CG and 0.60 CRthus no evolution is taking place.
Let’s suppose that there is an environmental change that makes red frogs more obvious to predators. How is the population affected and now the population consists of 36 green, 48 blue, and 6 red frogs?
Now, allele frequencies are changing and there is an advantage to being green or blue but NOT red. Evolution is indeed occurring.
Examine this Punnett square again. If p represents the allele frequency of CG (dominant) and q represents the allele frequency of CR (recessive) then two equations for a population in Hardy-Weinberg equilibrium can be derived where the following genotypes are represented by:
CGCG = p2CRCR = q2CGCR = 2pq
Mathematically then p + q = 0.60 + 0.40 = 1 (1st H-W equation)
So, the Punnett square effectively crossed (p + q ) (p + q ) which gives
p2 + 2pq + q2 = 1 (2nd H-W equation)