Question

In foxes, two alleles of a single gene, \(P\) and \(p,\) may result in lethality \((P P),\) platinum coat \((P p),\) or silver coat \((p p) .\) What ratio is obtained when platinum foxes are interbred? Is the \(P\) allele behaving dominantly or recessively in causing (a) lethality; platinum coat color?

Short answer

Answer: The ratio obtained when platinum foxes are interbred is 1:2:1 for lethality:platinum:silver. The P allele behaves recessively in causing lethality and dominantly in causing platinum coat color.

Step-by-step solution

Set up the Punnett square

To set up the Punnett square, we list the possible gametes from the two platinum foxes (\(Pp\)) along the top and side margins of the square. In this case, each platinum fox can produce two types of gametes: \(P\) and \(p\).

Fill the Punnett square with the offsprings' genotypes

Now, we can fill the square with the offspring genotypes by combining gametes. The Punnett square for this cross would look like: | | P | p | |---|---|---| | P | PP | Pp| | p | Pp | pp|

Find the resulting ratio

Identify the offspring genotypes from the Punnett square and count the instances of each genotype to find the resulting ratio. We have: 1 \(PP\) (lethality) 2 \(Pp\) (platinum coat) 1 \(pp\) (silver coat) Therefore, the ratio obtained when platinum foxes are interbred is 1:2:1 for lethality:platinum:silver.

Determine whether the P allele behaves dominantly or recessively in causing lethality and platinum coat color

(a) Lethality: The \(P\) allele causes lethality only in the homozygous \(PP\) condition, which means it behaves recessively in causing lethality, as it needs another \(P\) allele to exhibit the lethal trait. (b) Platinum coat color: The platinum coat occurs in the heterozygous \(Pp\) condition. In this case, the \(P\) allele is behaving dominantly, as the presence of one \(P\) allele is enough to produce a platinum coat color, and it masks the effect of the \(p\) allele.