5. On your Spring Break in Mexico, you take a break to count the starfish in a t

Question

5. On your Spring Break in Mexico, you take a break to count the starfish in a tidal pool. You notice that there is a rare recessive trait that causes the starfish to have 6 legs instead of 5. Of the 27 starfish you can find, only 1 has 6 legs. What are the allele frequencies for this population? Two years later, you return to the same beach and count the starfish again. This time you find 4 starfish out of 31 that have 6 legs. Are the genotype frequencies the same as two vears earlier? Test using Chi square. If it is not, calculate the new allele frequencies. Given that the current mutation rate is O and that there is no natural selection acting on these starfish, what is this random change in allele frequency called?) Seven years later, you come back to the beach. This time you can find no starfish with 6 legs. Given the most recent allele frequencies you know, is this what you would expect? (What is the complete loss of a allele called

Explanation / Answer

Given that in total 26 starfish are normal and 1 has 6 legs.

Genotypic frequency of 6 legs is 1/27 =0.037

Genotypic frequency is always 1 and is given by p2 +2pq +q2 =1

q2 = 0.037

q = 0.19

Allelic frequency = p+q =1

So

Frequecy of p = 1-0.19 = 0.81

After 2 years.

Chi-square value

So Ch-square - value is 0.112527

Genotypic frequency of 6 legs is 4/31 =0.129

q2 = 0.129

q = 0.35

P =1-0.35= 0.65

So new allelic frequency for 6 legs is 0.35

New allelic frequency for 5 legs is 0.65

This random change of allelic frequncy is called as genetic drift.

After seven years-

There is no starfish which has six legs. It might be due to fixation.

Fixation is a phenomenon where only one of the allele present in the population and other one is extinct from the population

Observed Expected O-E (O-E)2 (O-E)2/E 5 leg 0.81 0.65 0.16 0.0256 0.039385 6 leg 0.19 0.35 -0.16 0.0256 0.073143 0.112527

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