Genetics and Chi-square analysis 1. A trait in garden peas inv olves the curling
ID: 267651 • Letter: G
Question
Genetics and Chi-square analysis 1. A trait in garden peas inv olves the curling of leaves. A dihydrid cross was made involving a plant with yellow pods (yy) and curling leaves (cc) to a wild-type plant with green pods (YY) and normal leaves (CC). All the F1 offspring had green pods and normal leaves. The F1 plants were crossed to plants with yellow pods and curling leaves, the phenotypes and number of offspring of each phenotypes are indicated in the following, 200 green pods, normal leaves 250 yellow pods, curling leaves 50 green pods, curling leaves 55 yellow pods normal leave a. Conduct a Chi-square analysis to see if these two genes are linked, X2 (p=0.05, df-3)-7.82 (Hint: if these two genes are not linked, it will follow the law of independent assortment) b, if these two genes are linked, what are their genetic distance?Explanation / Answer
Answer:
a).
yy cc (yellow pods & curling leaves) x YY CC (green pods & normal leaves) ---Parents
YyCc (green pods & normal leaves) -------------------------------------------------------F1
YyCc (F1) x yycc ---------------------------Test cross
If the genes are not linked the progeny would be 1:1:1:1. It means that tha all progeny would be in equal (555/4 = 138.75) proportions.
It means that each expected phenotype number is 138.75
Chi-square value = 223.56
Degrees of freedom = 4-1 = 3
A chi-square of 223.56 is greater than the critical value (7.81), so we CAN reject the null hypothesis. Genes are linked.
b).
Hint: Recombinant progeny are less in number than non-recombinant progeny. So the recombinant progeny are green pods, curling leaves and yellow pods, normal leaves.
Recombination frequency = (no. of recombinants / Total progeny) 100
= (105 / 555)100
= 18.92%
Recombinantion frequency (%) = Distance between the genes
The two genes are linkes and the distance between the genes = 18.92 map units
Phenotype Observed(O) Expected (E) O-E (O-E)2 (O-E)2/E geen pods, normal leaves 200 138.75 61.25 3751.56 27.04 yellow pods, curling leaves 250 138.75 111.25 12376.56 89.20 geen pods, curling leaves 50 138.75 -88.75 7876.56 56.77 yellow pods, normal leaves 55 138.75 -83.75 7014.06 50.55 Total 555 555.00 223.56Related Questions
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