In carrying out crosses with the nematode Caenorhabditis elegans, a geneticist h
ID: 187023 • Letter: I
Question
In carrying out crosses with the nematode Caenorhabditis elegans, a geneticist hypothesizes that the allele for dumpy body shape (dpy) is recessive to the allele for normal body (dpy+), and the allele for uncoordinated (unc) is recessive to the coordinated body movement allele (unc+). Moreover, she hypothesizes that these two genes are unlinked (i.e., they assort independently). In a mating between a normal bodied, coordinated worm and a dumpy, uncoordinated worm, all of the F1 worms were normal bodied and coordinated in their movements. Selfing these F1's (it should be noted here that C. elegans are capable of self- fertilization) yielded an F2 generation with the following phenotypes:
o normal body, coordinated 95
o normal body, uncoordinated 21
o dumpy body, coordinated 19
o dumpy body, uncoordinated 25
TOTAL 160
a. What is the expected ratio and number of each class of F2 worms for this cross?
b. Determine the Chi-square (X2) value for the observed data under the proposed hypothesis.
c. What is the probability value for this Chi-square value?
d. Do these data support the hypothesis that these loci are unlinked? Explain.
Explanation / Answer
Answer:
Based on the given information:
F1: dpy+ unc+ x dpy unc
Progeny are all: dpy+ dpy unc+ unc
F2 Self cross: dpy+ dpy unc+ unc x dpy+ dpy unc+ unc
Punnett Square for F2 cross:
Phenotype:
Phenotypic ratio 9:3:3:1
Chi Square Test:
Degree of freedom = number of categories - 1 = 4 - 1 = 3
P-Value corresponding to Chi square value of 29.511 with 3 degree of freedom is P-Value is < 0.00001.
The result is significant at a significance level of 0.05. Therefore Null Hypothesis is rejected. Based on the evidence, there is significant difference in observed frequency from expected frequency.
dominant recessive normal body dpy+ dpy dumpy body coordinated body movement unc+ unc uncoordinated body movementRelated Questions
drjack9650@gmail.com
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.