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; (b) platinum coat color?

Short answer

Answer: The phenotypic ratio in the offspring when platinum foxes are interbred is 1:2:1 (lethality:platinum:silver). The P allele is considered dominant in causing lethality and incompletely dominant in causing the platinum coat color.

Step-by-step solution

Determine the genotypes of the platinum foxes to be crossed

The platinum foxes have the genotype Pp, as mentioned in the exercise.

Set up a Punnett square

A Punnett square is a table that helps to predict the genotypes of offspring from a particular cross. In this case, we are crossing two platinum foxes with the genotype Pp. Create a 2x2 table with P and p along the top representing one parent and P and p along the side representing the other parent.

Fill in the Punnett square

Fill in the Punnett square by combining the alleles from each parent. The top-left cell combines the "P" from the top and "P" from the side, resulting in "PP". The top-right cell combines the "P" from the top and "p" from the side, resulting in "Pp". The bottom-left cell combines the "p" from the top and "P" from the side, resulting in "Pp". The bottom-right cell combines the "p" from the top and "p" from the side, resulting in "pp".

Determine the genotypic ratio

The genotypic ratio is the ratio of the different genotypes in the offspring. To determine this ratio, count the number of each genotype in the Punnett square: - PP: 1 offspring - Pp: 2 offspring - pp: 1 offspring So the genotypic ratio is 1:2:1.

Determine the phenotypic ratio

The phenotypic ratio is the ratio of the different phenotypes in the offspring. According to the exercise, PP results in lethality, Pp results in a platinum coat, and pp results in a silver coat. Count the number of each phenotype in the Punnett square: - Lethality: 1 offspring (PP) - Platinum coat: 2 offspring (Pp) - Silver coat: 1 offspring (pp) So the phenotypic ratio is 1:2:1 (lethality:platinum:silver).

Determine the dominancy behavior for lethality and platinum coat color

(a) Lethality: The P allele results in lethality when it is present in the homozygous state (PP). This means that the P allele behaves dominantly in causing lethality, as it is sufficient for it to be present in a homozygous state to cause the lethal phenotype. (b) Platinum coat color: The platinum coat color is observed in the offspring when the genotype is heterozygous (Pp). This indicates that the P allele behaves incompletely dominantly in causing the platinum coat color since it needs to be present with the p allele to produce the platinum coat phenotype.

Key concepts

Genotypic Ratio

Understanding the genotypic ratio is a cornerstone in grappling with inheritance patterns. It provides a numerical relationship between different genotypes resulting from a particular genetic cross.

For example, let's consider a cross between two platinum-coated foxes with genotypes Pp. Upon setting up a Punnett square for this cross, we observe the formation of offspring with the genotypes PP, Pp, and pp. The count for each type yields a genotypic ratio, in this scenario, of 1:2:1. This tells us that for every one offspring with genotype PP, there are two offspring with genotype Pp, and one with genotype pp.

This ratio is imperative for predicting the likelihood of an offspring inheriting a particular combination of alleles. Thus, knowing the genotypic ratio can help foretell the diversity within a population, informing selective breeding strategies and genetic counseling.

Phenotypic Ratio

While genotypic ratios illustrate the genetic blueprint of an organism, the phenotypic ratio reveals the observable characteristics, or phenotypes. This ratio indicates the frequency of distribution of traits among offspring.

In the fox example, the genotype PP results in lethality, thus they don't contribute to the phenotypic ratio as they do not survive. The genotype Pp leads to a platinum coat, and pp results in a silver coat. Our Punnett square analysis provides us with a phenotypic ratio for the surviving offspring of 2:1, representing platinum to silver coats, respectively.

This information is critical for breeders or researchers who wish to understand the visual outcome of certain genetic crosses, and it is also useful for teaching Mendelian inheritance where certain alleles lead to dominant or recessive phenotypes.

Allele Dominance

Allele dominance describes how different forms of a gene, or alleles, interact to produce a particular phenotype. An allele can be dominant, recessive, or exhibit incomplete dominance or co-dominance.

In our exercise, two inheritance patterns are distinct:

• The allele causing lethality, P, is dominant as it induces death in the homozygous condition (PP).
• Conversely, for the platinum color phenotype, the P allele displays incomplete dominance. Here, the presence of both P and p alleles (heterozygous state Pp) is necessary to manifest a platinum coat.

Becoming familiar with allele dominance is invaluable in predicting the possible traits of offspring and is integral to the study of genetics in medical, agricultural, and ecological contexts.

Inheritance Patterns

Inheritance patterns explain how traits and characteristics are passed down from parents to offspring through their genetic codes. The mode of inheritance can vary widely, depending on whether a gene is located on a sex chromosome or an autosome, and whether it’s dominant, recessive, or exhibits other forms of dominance such as incomplete or co-dominance.

In the case of the fox population, we see a classic Mendelian inheritance where alleles are either dominant or show incomplete dominance. The interbreeding of platinum foxes (Pp) unveils such patterns where different combinations of P and p alleles result in various phenotypes, a fundamental aspect in understanding genetics.

Grasping the nuances of inheritance patterns lays a foundation for uncovering more complex genetic interactions and can be pivotal in fields like genetic therapy, conservation biology, and evolutionary studies.