Consider the following dihybrid cross involving two of Mendel\'s genes in pea pl
ID: 191502 • Letter: C
Question
Consider the following dihybrid cross involving two of Mendel's genes in pea plants that assort independently and exhibit simple dominance (W-violet flowers; w white flowers. T-axial flower position; t -terminal flower position). A plant with white, axial flowers was crossed with a plant that had violet, terminal flowers. All F1 progeny have violet, axial flowers. F1 plants are selfed to yield: (5 points) 653 plants with violet, terminal flowers 1756 plants with violet, axial flowers 702 plants with white, axial flowers 234 plants with white, terminal flowers a. b. c. d. What is your expected phenotypic ratio for the progeny from this cross? How many individuals would you expect in each phenotypic class among the progeny? Calculate the chi-square value rounded to two decimals, and the degrees of freedom. Do the results observed differ significantly from those expected at pExplanation / Answer
1.What is the expected phenotypic ratio for the progeny from this cross?
Observed frequencies:
PHENOTYPE
FREQUENCY
Violet Axial
1756
Violet terminal
653
white Axial
702
white terminal
234
Total
3345
Expected ratios for unlinked traits:
TRAITS
RATIO
Violet Axial
9
Violet terminal
3
white Axial
3
white terminal
1
2. How many individuals would you expect in each phenotypic class among the progeny?
Violet Axial
Violet terminal
white Axial
white terminal
Total
Observed (O)
1756
653
702
234
3345
Expected (E)
1881.56
3345*9/16
627.187
3345*3/16
627.187
3345*3/16
209.06
3345*1/16
3345
3. Calculate the chi square value rounded to two decimals, and the degree of freedom.
Violet Axial
Violet terminal
white Axial
white terminal
Observed ( O)
1756
653
702
234
Expected (E)
1881.56
627.187
627.187
209.06
O-E
-125.56
25.813
74.813
24.94
(O-E)2/E
8.37
1.062
8.923
2.97
x2=(8.37+1.062+8.923+2.97)=21.325
Determine the degree of freedom (df)
In order to determine if the chi-squared value is statistically significant a degree of freedom must first be identified
The degree of freedom is calculated from the table of frequencies according to the following formula:
df = (m – 1) (n – 1)
Where: m = number of rows ; n = number of columns
For all dihybrid crosses, the degree of freedom should be: (number of phenotypes – 1)
4. Do the results observed differ significantly from those expected at p<0.05
Yes, the results observed differ significantly from those expected at p<0.05
PHENOTYPE
FREQUENCY
Violet Axial
1756
Violet terminal
653
white Axial
702
white terminal
234
Total
3345