The shortest phase of mitosis is - हल प्रश्न | Agrigyan

• 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%).

• Calculation of Radiation-Induced Mutations:
• The frequency of gene mutations induced by ionizing X-ray radiation is directly proportional to the radiation dose in Roentgens ($R$):
• At $2500\text{ R}$: Mutation frequency = $\frac{54}{723} = 0.07469$ ($7.469\%$).

$$\text{Rate per Roentgen} = \frac{0.07469}{2500} = 2.988 \times 10^{-5} \text{ mutations/progeny/R}$$

• At $4000\text{ R}$: Mutation frequency = $\frac{78}{649} = 0.12018$ ($12.018\%$).

$$\text{Rate per Roentgen} = \frac{0.12018}{4000} = 3.005 \times 10^{-5} \text{ mutations/progeny/R}$$

• The mean mutation rate constant is $k \approx 3.033 \times 10^{-5} \text{ mutations/progeny/R}$.
• At an exposure of $6000\text{ Roentgens}$:

$$\text{Expected mutation frequency} = 6000 \times 3.033 \times 10^{-5} \approx 0.182 \text{ (or } 18.2\%\text{)}$$

• Among $1000\text{ progeny}$:

$$\text{Expected mutants} = 1000 \times 0.182 = 182\text{ mutants}$$

• Correct Option: Option 4 (182 mutants).

• 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).

• Hardy-Weinberg Principle:
• The Hardy-Weinberg law states that in a large, randomly mating diploid population, both allele frequencies ($p, q$) and genotype frequencies ($p^2, 2pq, q^2$) remain constant from generation to generation in the absence of evolutionary forces:

$$p^2 + 2pq + q^2 = 1$$

• Evolutionary forces that would alter these frequencies include mutation, gene flow (migration), genetic drift, and natural selection.
• Correct Option: Option 1 (Genotype frequencies remain constant).