The Fascinating World of Genetic Crosses
What is the phenotypic ratio of the offspring when crossing two Mexican hairless dogs?
Given a phenotypic ratio of 1/3 hairy and 2/3 hairless, can you draw a Punnett square for this cross and indicate the phenotype for each possible offspring?
Predicted Genotypes and Phenotypes of Offspring:
From the Punnett square:
- Phenotypes: 1/3 hairy (Hh), 2/3 hairless (Hh or hh)
- Genotypes of the P1 dogs: heterozygous (Hh)
- Genotypes of the F1 dogs: 1/3 hh; 2/3 Hh
The genetic cross of two Mexican hairless dogs results in a phenotypic ratio of 1/3 hairy and 2/3 hairless offspring. This indicates that the hair phenotype is controlled by a single gene (monogenic) with a lethal allele (H allele).
In this scenario, designing a true-breeding cross to yield an all hairless offspring is not feasible due to the presence of a lethal allele. The homozygous HH genotype is lethal, making it impossible to have all hairless individuals.
Lethal alleles, like the H allele in this case, result in the death of organisms when present in a homozygous state. Heterozygous individuals survive and may display a normal or altered (non-lethal) phenotype.