During the Summer at Hogwarts, Hagrid passes his time by breeding Hungarian Horn

Question

During the Summer at Hogwarts, Hagrid passes his time by breeding Hungarian Horntail dragons. When he bred together two black parents, he obtained yellow, black, and brown dragons in the ratio. 4 yellow : 9 black: 3 brown.

a. How many genes control colour in these dragons? Why?

b. Use symbols to explain the phenotypes of the parents, and for each phenotypic category in the offspring.

c. Dumbledore is especially fond of the brown variety. What is the probability that any single brown dragon will be true-breeding?

Explanation / Answer

Two genes each with two alleles control dragon color.
It is a dihybrid cross between AaBb X AaBb parents
where,
A_B_ = 9 = Black
aa_ _ = 4 = Yellow
_ _bb = 3 = Brown

Brown phenotype is seen in 2 genotypes: They are,
AAbb = 1/16 = Homozygous at both loci (You can consider this as pure breeding)
Aabb = 2/16
Total = 3/16

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