A genetic survey revealed that a population of spruce trees contained 2 alleles
ID: 218688 • Letter: A
Question
A genetic survey revealed that a population of spruce trees contained 2 alleles (B and b) for a gene affecting color of the needles. The survey of 10,000 individuals found the 3 possible genotypes in the following abundances:
(a) What are the frequencies of alleles B and b in this sample?
(b) How many of each genotype class would have been found if the population effectively
approximated the Hardy-Weinberg equilibrium?
(c) Estimate the value of the inbreeding coefficient (F) for this population given these data.
Genotype BB Bb bb Number found 4428 3604 1968Explanation / Answer
a) Allele frequency estimation:
Genotype
Freequency
Allele B
Allele b
Total
BB
4428
8856
0
8856
Bb
3604
3604
3604
7208
bb
1968
0
3936
3936
Total
10000
12460
7540
20000
Allele frequency = Number of individual alleles/Total number of alleles…
Allele B
= 12460/20000
0.62
Allele b
= 7540/20000
0.38
b) Expected frequency estimation:
BB
=0.62*0.62 = 0.388
*10000= 3881
Bb
= 2 * 0.62 * 0.38 = 0.470
*10000= 4697
bb
= 0.38 *0.38 = 0.142
*10000= 1421
c) inbreeding coefficient = (# of Expected Heterozygotes - # of observed Heterozygotes) / (# of Expected Heterozygotes
= 4697-3604 / 4697 = 0.232
Genotype
Freequency
Allele B
Allele b
Total
BB
4428
8856
0
8856
Bb
3604
3604
3604
7208
bb
1968
0
3936
3936
Total
10000
12460
7540
20000
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