A true breeding strain of squash that produced disk-shaped fruits was crossed to
ID: 13295 • Letter: A
Question
A true breeding strain of squash that produced disk-shaped fruits was crossed to a true-breeding strain that produced long fruits. All the plants in the F1 have disk-shaped fruits. The progeny from a self-fertilized F1 plant showed a new phenotype , spherical fruits. The number of plants with each phenotype in the F2 is:
Long fruits: 32
Spherical fruits: 178
Disk fruits: 270
The phenotypic ratio: AB : aaB : Abb : aabb
Disc : sphere : sphere : Long
9 : 3 : 3 : 1
i.e. 9 (disc) : 6 (sphere) : 1 (long)
So, the resulted F2 generation are in 9 : 6 : 1 indicating that alleles with A-bb and aa-B has same appearance and the dominant alleles i.e. A & B are semi-dominant epistatic.
1. So, the question is: Use a chi-square test to test your hypothesis( i.e does the observed distribution of phenotypes match what you would expect based on your predictions?)
Explanation / Answer
OBSERVED
EXPECTED
O-E
(O-E)^2
(O-E)^2/E
Long fruits
32
30
2
4
0.13
Spherical fruits
178
180
2
4
0.13
Disk fruits:
270
270
0
0
0
480
0.26
CALCULATED VALUES
0.26
ARE LESS THAN TABLE VALUE AT 5% --- 3.18 , SO
ACCEPT THE HYPOTHIES
alleles with A-bb and aa-B has same appearance and the dominant alleles i.e. A & B are semi-dominant epistatic
OBSERVED
EXPECTED
O-E
(O-E)^2
(O-E)^2/E
Long fruits
32
30
2
4
0.13
Spherical fruits
178
180
2
4
0.13
Disk fruits:
270
270
0
0
0
480
0.26
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