• Definition of Penetrance:
• Penetrance: The proportion or percentage of individuals carrying a specific dominant or homozygous recessive genotype who actually express the corresponding clinical or morphological phenotype:

$$\text{Penetrance (\%)} = \frac{\text{Individuals showing phenotype}}{\text{Total individuals carrying genotype}} \times 100$$

• If $20\%$ of heterozygous individuals ($Pp$) do not express polydactyly (incomplete penetrance), then the proportion that expresses the trait is:

$$\text{Penetrance} = 100\% - 20\% = 80\%$$

• Correct Option: Option 4 (80%).

• Non-Epistatic Genetic Interactions:
• Complementary Gene Action: Occurs when two or more independent, non-allelic genes in distinct biochemical pathways each contribute essential functional products required to manifest a single specific phenotypic trait.
• Absence of the dominant allele at either locus halts the phenotypic pathway, producing a modified dihybrid ratio of $9:7$.
• Correct Option: Option 2 (Complementary gene action).

• Secondary Circulation in Fishes:
• The secondary vascular system in teleost fishes consists of a fine, low-pressure network of capillary vessels running parallel to the primary blood circulation, supplied through anastomoses from the primary system.
• Functions: Serves the external body surface, gills, fins, and eyes, mediating cutaneous respiration, heat exchange (counter-current rete mirabile), osmoregulation, and regional endothermy (eye warming).
• It does not function in non-respiratory nutrient transport, which is handled by the primary systemic vasculature and portal systems.
• Correct Option: Option 2 (Non-respiratory nutrient transport).

• Wild-Type Allele: The allele that occurs with the highest frequency in a natural, wild population is designated as the wild type. It is typically considered the standard or baseline functional allele responsible for the typical wild phenotype.
• Mutant Allele: Any alternative form of an allele that arises through spontaneous or induced mutation and is present at a significantly lower frequency.
• nalysis:
• (Wild type): Correct. Represents the predominant, naturally occurring allele in wild populations.
• (Carrier type): Refers to heterozygous individuals carrying a recessive allele without phenotypic manifestation.
• (Mutant type): A modified allele, typically rare.
• (Semi lethal type): Allele that causes mortality in a proportion of individuals possessing it.

Correct option: (2) Wild type