Answer:
a. Montezuma phenotype is given by a dominant allele.
b. 8 MmFf : Montezuma and normal fins (1/2) and 8 mmFf: green body and normal fins (1/2)
c. 9/16 Montezuma and normal fin, 3/16 Montezuma and ruffled fin, 3/16 Green body and normal fin, 1/16 Green body and ruffled fin.
Explanation:
a. Montezuma is a single-gene trait, and according to the description, after a cross of two heterozygous fishes offspring showed these phenotypic ratios:
- 2/3 montezuma
- 1/3 wild-type
If parentals are heterozygous and the vast majority of the progeny has the montezuma phenotype, it is probable that montezuma phenotype is related to a dominant allele. If M is montezuma allele and m wild-type, this cross can be seen in the first Punnett Square, and the progeny is:
- 1/4 MM Montezuma
- 2/4 Mm Montezuma
- 1/4 mm wild-type
These proportions are the same that reported ones. Therefore, montezuma is inherited in a dominant way.
b. The fin phenotype is given by F/f gene, where F: normal fin, f: ruffled fin. If a montezuma fish homozygous for normal fins (MmFF) is crossed with a green, ruffled fish (mmff), the progeny will be:
- 8 MmFf : Montezuma and normal fins (1/2)
- 8 mmFf: green body and normal fins (1/2)
This cross is explained in the Punnett Square 2.
c. Montezuma fishes from part b are MmFf. They have montezuma body color and normal fins.
If two individuals MmFf are crossed, it will produce the following offspring (as it is shown in the final Punnett Square):
- 9/16 Montezuma and normal fin
- 3/16 Montezuma and ruffled fin
- 3/16 Green body and normal fin
- 1/16 Green body and ruffled fin.
