A true breeding LARGE MOUTH bass (fish) was crossed with a true-breeding SMALL M

Question

A true breeding LARGE MOUTH bass (fish) was crossed with a true-breeding SMALL MOUTH bass. All of the offspring had SMALL MOUTHS. Answer the following based on crossing two of the SMALL MOUTH hybrids:

Assign letters to the alleles for each trait

Provide the genotypes for the following:

LARGE MOUTH parent

SMALL MOUTH parent

F1 Hybrid that had a SMALL MOUTH

Name the type of cross that is being performed when two hybrids are crossed.

Provide the PHENOTYPIC ratio for the F2 generation.(label your answer)

Provide the GENOTPYIC ratio for the F2 generation. (label your answer)

Explanation / Answer

Answer:

Since the F1 hybrids have small mouth, small mouth is dominant over large mouth.

a. Alleles for large mouth = m

Alleles for small mouth = M

b. Genotype of large mouth parent = mm

c. Genotype of small mouth parent = MM

d. Cross:

Parents: MM (Small) x mm (Large)

F1: Mm (Small mouth)

So, genotype of the F1 hybrid with small mouth = Mm

e. The type of cross that is being performed is monohybrid cross since only one trait is involved.

f. Cross: Mm (Small) x Mm (Small)

F2: MM (Homozygous Small), Mm (Heterozygous small), Mm (Heterozygous small), mm (Large)

So, phenotypic ratio for F2 generation:

Small mouth : Large mouth = 3 : 1

g. Genotypic ratio for F2 generation:

MM (Homozygous Small), Mm (Heterozygous small), mm (Large) = 1: 2: 1

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