Question

Theo wants to breed and sell stegosaurus dinosaurs. They went to Jurassic park and captured a homozygous purple stegosaur and a homozygous pink stegosaur. A scientist at the park told them the pink color was an autosomal recessive trait.

Describe how Theo could use their two dinosaurs to breed a population of all pink stegosaurs to sell. Include the phenotypic and genotypic ratios of offspring in each generation (F1, F2, etc.)

Answer 1

Theo can use the principles of Mendelian inheritance to selectively breed stegosaurs with the desired pink colour. Let's denote the purple colour as "P" (dominant) and the pink colour as "p" (recessive).

Note: that with Mendelian genetics, the recessive trait will only express itself in pairs of 2 recessive alleles. In other words, the dominant allele will be observed as the dominant phenotype.

1st Generation

• Theo breeds homozygous purple stegosaur (PP) with homozygous pink stegosaur (pp).
• The offspring (F1 generation) will all be heterozygous (Pp), and phenotypically, they will be purple.
• Genotypic ratio: 100% Pp
• Phenotypic ratio: 100% Purple

Second generation

• Theo breeds two F1 heterozygous stegosaurs (Pp) together.
• The possible genotypes of the F2 generation are PP, Pp, and pp. However, only those with the pp genotype will exhibit the pink phenotype.
• Genotypic ratio: 25% PP, 50% Pp, 25% pp
• Phenotypic ratio: 75% Purple, 25% Pink

Third generation and beyond

• To ensure a population of all pink stegosaurs, Theo needs to selectively breed individuals with the pp genotype.
• Breeding two pink stegosaurs (pp) together will always produce pink offspring (pp).
• Genotypic ratio: 100% pp
• Phenotypic ratio: 100% Pink