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beardy beardy
wrote...
Posts: 166
10 years ago
You discover a population of aye ayes. You notice variation in ear color. It turns out the E gene determines ear color, and that there is incomplete dominance. EE individuals have black ears, ee individuals have grey ears, and Ee individuals have brown ears. There are 200 individuals with blacks, 400 with brown ears and 400 with grey ears. Does this population appear to be evolving? Use a Chi-Square test to determine if your observed frequencies fit your expected frequencies. This is the formula for Chi-squared:



Even though there are three phenotypes, the degrees of freedom is 1. Use a Chi-squared table (http://www.medcalc.org/manual/chi-square-table.php) and assume that any Chi-squared value over the critical value for 0.05 is significant. Show your work.
Looking at the actual observed vs. expected frequencies, can you speculate on what is going on evolutionarily.
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Replies
wrote...
Donated
Valued Member
10 years ago
Out of 2000 alleles,
800 E, 1200 e
p = 0.4, q = 0.6

Expected:
(.42*1000) 160 Black,
(2(.4)(.6)*1000) 480 Brown,
(.62*1000) 360 Grey.

Chi-Square:
(200-160)2/160 + (400-480)2/480 + (400-360)2/360 = 27.77....

Since 27.77 > 3.841 we reject the null hypothesis, and conclude that evolution can be working on this population. 

My guess is that the brown heterozygotes are underrepresented because brown ears do not have an advantage (black/grey ears are preferable for camouflaging, eg.).  That part is a total guess though.  Let me know how this question turns out if you find the right answer.
Pretty fly for a SciGuy
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