In a plant, two genes have cumulative influence on the weight of fruits. Each dominant allele adds $10$ g to a minimum basic weight of $30$ g. In a cross between dihybrid plants having fruits weighing $50$ g each, what percentage of the offspring would have fruits weighing $40$ g?

12.5 %

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25 %

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37.5 %

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50 %

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Solution

The correct option is A $25 %$
Gametes AB Ab aB ab
AB AABB=70g AABb=60g AaBB=60g AaBb=50g
Ab AABb=60g AAbb=50g AaBb=60g Aabb=40g
aB AaBB=60g AaBb=50g aaBB=50g aaBb=40g
ab AaBb=50g Aabb=40g aaBb=40g aabb=30g
Let the weight be controlled by two genes A and B having recessive allele as a and b.
Minimum basic weight is provided to be 30g so genotype of such fruit bearing plant will be all recessive(aabb).,
Since we know each dominant allele adds 10g to the base weight of 30g. So, for a plant to have a fruit of 50g it is required to have 2 dominant alleles. Since it is mentioned to us that the plant is dihybrid so one dominant allele of both the genes will be present in the parent plant having fruit weight of 50g. So, the genotype of parent plant comes out to be-AaBb
A dihybrid cross between AaBb X AaBb gives following results as shown in the table:
So, after evaluation of all the weights of fruits in progeny pkants we find that 4 plants out of 16 will give fruits of 40g weight.
So, the percentage will be = 4/16 x 100 = 25%.

So, the correct answer to the question is '25%'.

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Gametes	AB	Ab	aB	ab
AB	AABB=70g	AABb=60g	AaBB=60g	AaBb=50g
Ab	AABb=60g	AAbb=50g	AaBb=60g	Aabb=40g
aB	AaBB=60g	AaBb=50g	aaBB=50g	aaBb=40g
ab	AaBb=50g	Aabb=40g	aaBb=40g	aabb=30g

In a plant, two genes have cumulative influence on the weight of fruits. Each dominant allele adds 10g to a minimum basic weight of 30g. In a cross between dihybrid plants having fruits weighing 50g each, what percentage of the offspring would have fruits weighing 40g?

In a plant, two genes have cumulative influence on the weight of fruits. Each dominant allele adds $10$ g to a minimum basic weight of $30$ g. In a cross between dihybrid plants having fruits weighing $50$ g each, what percentage of the offspring would have fruits weighing $40$ g?