In the nematode, Caenorhabditis elegans, there are two mutations, dumpy (dmp) an

ID: 312823 • Letter: I

Question

In the nematode, Caenorhabditis elegans, there are two mutations, dumpy (dmp) and uncoordinated (unc). These animals have two sexes, male and hermaphrodite. Hermaphrodites will reproduce by self-fertilization. A heterozygous hermaphrodite dmp* dmp unc* unc is allowed to self-fertilize and her offspring are examined. The data are shown in Table 1. Do these two genes appear to assort independently? Calculate a x^2 value to answer this question. Justify your answer. Assort independently (circle correct answer) Yes No Justification______ _____ _____ _____

Explanation / Answer

Assume that, dmp+ = A; dmp = a; unc = B; unc = b.

The self-cross of heterozygotes will have the progeny in the ratio of 9:3:3:1.

Total number of offspring is = 1600

The expected frequencies are,

Aa Bb -à 1600 *9/16 = 900

Aa bb -à 1600 *3/16 = 300

aa Bb -à 1600 *3/16 = 300

Aa bb -à 1600 *1/16 = 100

CHI - SQUARE (X2):

X2 = (O - E)2 / E

Where O = Observed frequency

E = Expected frequency

Phenotype

(O-E)

(O-E)^2

(O-E)^2/E

AaBb

864

900

-36

1296

1.44

Aabb

339

300

1521

5.07

aa Bb

311

300

1.5

2.25

0.155172

aa bb

100

-14

196

1.96

6.665172

The chi-square value is = 6.665

Degrees of freedom is = n-1 = 3

The calculated P value is 0.083378, which is not significant at p< 0.05. So, we accept the null hypothesis.

The difference between the expected an observed phenotypic ratios is not significant and the genes are assorting independently.