Females heterozygous for the recessive second chromosome mutations px, sp, and cn are mated to a male homozygous for all three mutations.The offspring are as follows:
$\begin{array}{|l|r|}
\hline p x s p c n & 1461 \
\hline p x s p c n^{+} & 3497 \
\hline p x s p{+ c n} & 1\
\hline p x s p^{+} c n+ & 11 \
\hline p x^{+} s p c n & 9 \
\hline p x^{+} s p c n+ & 0 \
\hline p x^{+} s p+ c n & 3483 \
\hline p x^{+} s p+ c n+ & 1539 \
\hline & 10,000 \
\hline
\end{array}$
-What is the coefficient of coincidence in this region?
A)0
B)0.16
C)0.33
D)0.5
E)0.66

Question

Females heterozygous for the recessive second chromosome mutations px, sp, and cn are mated to a male homozygous for all three mutations.The offspring are as follows:
 $\begin{array}{|l|r|}
\hline p x  s p  c n & 1461 \
\hline p x  s p  c n^{+} & 3497 \
\hline p x  s p{+ c n} & 1\
\hline p x  s p^{+}  c n+ & 11 \
\hline p x^{+}  s p  c n & 9 \
\hline p x^{+}  s p  c n+ & 0 \
\hline p x^{+}  s p+ c n & 3483 \
\hline p x^{+}  s p+ c n+ & 1539 \
\hline & 10,000 \
\hline
\end{array}$
-What is the coefficient of coincidence in this region?
A)0
B)0.16
C)0.33
D)0.5
E)0.66

Quizplus · Accepted Answer

The coefficient of coincidence (COC) is calculated as the observed double recombinants divided by the expected double recombinants. The observed double recombinants are the offspring that show recombination for both traits, which are the ones with low counts (1 and 11), totaling 12. The expected double recombinants can be calculated by multiplying the recombinant frequencies of each gene pair. The recombinant frequency for px-sp can be found by adding the recombinants for these genes (11+1)/(10,000) = 0.0012, and for sp-cn by adding their recombinants (3483+1539)/(10,000) = 0.5022. Multiplying these gives an expected frequency of 0.0012 * 0.5022 = 0.0006. The total expected double recombinants would be 0.0006 * 10,000 = 6. The COC is then 12 observed / 6 expected = 2. However, this calculation seems to misunderstand the question's intent, which is to calculate the COC as the observed double recombinants over the expected based on independent assortment frequencies. The correct approach involves calculating the expected double recombinants based on the single recombination frequencies between each gene pair, not directly from the observed counts. Given the misunderstanding in the calculation, let's correct the approach:To calculate the coefficient of coincidence (COC), we first need to determine the expected number of double recombinants if crossing over events were independent. The COC is defined as the ratio of the observed number of double recombinants to the expected number of double recombinants.The expected number of double recombinants can be calculated by multiplying the frequencies of the single crossovers and then by the total number of offspring. However, without clear single crossover frequencies provided directly, and given the misunderstanding in the initial explanation, we cannot accurately calculate the COC without the correct formula and data interpretation.The correct calculation involves understanding the genetic distances between the genes and using them to estimate the expected number of double recombinants. Since the initial explanation led to a confusion rather than a clear answer, and without re-calculating based on the correct genetic distances and frequencies, the selection of "B) 0.16" as the correct answer was premature and not based on a correctly outlined calculation process here. For a precise calculation, one would typically use the formula: COC = (Number of observed double recombinants) / (Number of expected double recombinants based on independent assortment). The expected number is often calculated from the product of the distances between genes (as probabilities), but without these distances or a clear method to calculate them from the provided data, the correct COC calculation process was not accurately described. Given the data and the typical approach to calculating COC, a reevaluation of the calculation method is necessary for an accurate answer.

Females Heterozygous for the Recessive Second Chromosome Mutations Px, Sp