Matings between hairless & normal dogs always produce hairless & normal offspring in a 1:1 ratio. In matings of two hairless dogs, hairless & normal dogs are always produced in a 2:1 ratio. How can these results be explained?
The given results can be explained by the principles of genetics, specifically pertaining to the inheritance of a particular trait, in this case, the presence or absence of hair in dogs. To understand the explanation, we need to consider the concept of dominant and recessive traits.
In genetics, traits are determined by genes present on the chromosomes. Each gene has different forms called alleles. In the case of hairiness in dogs, let's assume that the gene controlling this trait has two different alleles: H for hairlessness (dominant) and h for the presence of hair (recessive).
When a hairless dog mates with a normal (hairy) dog, there are two possible scenarios. If the hairless dog is homozygous for the hairless allele (HH), meaning it possesses two copies of the hairless allele, and the normal dog is homozygous for the hairy allele (hh), meaning it has two copies of the hairy allele, then their offspring will always inherit one copy of the hairless allele (H) from the hairless parent and one copy of the hairy allele (h) from the normal parent. This results in a 100% hairless to hairy ratio in the offspring, meaning all the puppies will be hairless.
On the other hand, if the hairless dog is heterozygous for the hairless allele (Hh) and the normal dog is homozygous for the hairy allele (hh), then their offspring have a 50% chance of inheriting the hairless allele (H) from the hairless parent and a 50% chance of inheriting the hairy allele (h) from the normal parent. This results in a 1:1 ratio of hairless to hairy puppies.
Now, when two hairless dogs mate, both parents are homozygous for the hairless allele (HH). In this case, the offspring have a 66.7% (2/3) chance of inheriting the hairless allele (H) from one parent and a 33.3% (1/3) chance of inheriting the hairy allele (h) from the other parent. This results in a 2:1 ratio of hairless to hairy puppies.
Therefore, the observed results of hairless to hairy ratios in the given scenarios can be explained by the way the alleles for hairlessness and hairiness are inherited and the possible combinations that arise during mating between dogs with different genotype for the hairlessness trait.