What is the probability that a sighted dog carries the gene for blindness if it is crossed with one that does? - briefly
The probability that a sighted dog carries the gene for blindness can be determined by examining its parentage and genetic history. If the dog's lineage includes ancestors known to carry the recessive gene responsible for blindness, the likelihood increases significantly. However, without such familial information, it is challenging to ascertain the exact probability.
What is the probability that a sighted dog carries the gene for blindness if it is crossed with one that does? - in detail
The probability that a sighted dog carries the gene for blindness when mated with another dog that carries the gene can be understood by examining the genetic principles governing inheritance patterns in dogs, particularly focusing on the genes responsible for vision.
In many species, including dogs, eye color and certain visual impairments are determined by autosomal recessive genes. This means that an individual must inherit two copies of a recessive gene (one from each parent) to exhibit the trait. For blindness, let's denote the normal vision allele as "B" and the blindness allele as "b". A dog can have one of three genotypes: BB (homozygous dominant), Bb (heterozygous), or bb (homozygous recessive). Only dogs with the bb genotype will be blind.
When a sighted dog (BB or Bb) is mated with a blind dog (bb), we need to determine the probability that the sighted dog carries the gene for blindness, i.e., it has the Bb genotype. To do this, we use Mendelian inheritance principles and consider the potential outcomes of such a mating:
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If the sighted dog is homozygous dominant (BB): It does not carry the gene for blindness. All offspring will be heterozygous (Bb) and will have normal vision, as the recessive trait is masked by the dominant one.
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If the sighted dog is heterozygous (Bb): It carries one copy of the gene for blindness. In this case, there is a 50% chance that any given offspring will also be heterozygous (Bb) and thus carry the gene for blindness.
To determine the probability that the sighted dog carries the gene for blindness, we need to consider the frequency of each genotype in the population. Generally, the frequency of homozygous recessive individuals (bb) is low due to the rarity of double recessive alleles in a large population. Therefore, it is more likely that a sighted dog carrying the gene for blindness has the Bb genotype rather than BB.
In summary, if a sighted dog is mated with one that carries the gene for blindness (bb), there is a high probability that the sighted dog itself carries the gene for blindness and has the Bb genotype. The exact numerical probability would depend on the specific allele frequencies in the population, but generally, it can be considered highly likely.