Energy & Proteins

• Wright's Coefficient of Relationship ($R$):
• Defined as the proportion of genes shared identical by descent between two relatives:

$$R_{XY} = \sum \left(\frac{1}{2}\right)^L$$

where $L$ is the number of steps in each genealogical path through a common ancestor.

• Single First Cousins: Share 2 common grandparents through 1 set of siblings:

$$R = 2 \times \left(\frac{1}{2}\right)^4 = \frac{2}{16} = 0.125$$

• Double First Cousins: Two siblings of one family marry two siblings of another family. Their children share all 4 grandparents through 4 independent paths:

$$R = 4 \times \left(\frac{1}{2}\right)^4 = \frac{4}{16} = \frac{1}{4} = \mathbf{0.25}$$

• nalysis:
• (0.25): Correct.

Correct option: (3) 0.25

• Dietary Cation-Anion Difference (DCAD) and Milk Fever Prevention:
• Parathyroid hormone (PTH) acts on bone and kidney to maintain plasma calcium homeostasis:
• Metabolic Acidosis (Acidotic state): Induced by feeding anionic salts (negative DCAD diets). Acidosis optimizes the conformation of PTH receptors, markedly increasing the sensitivity of bone osteoclasts to PTH and promoting bone calcium resorption.
• Metabolic Alkalosis (Alkalotic state): Induced by excess dietary cations ($K^+, Na^+$). Alkalosis induces a refractory state where bone receptors become insensitive to PTH, impairing calcium mobilization and precipitating hypocalcemia (milk fever).
• Therefore, the assertion that an alkalotic state increases bone sensitivity to PTH is scientifically false (not true).
• nalysis:
• Statement 1 is incorrect/not true, hence the correct answer.

• Photochemical Synthesis of Vitamin D:
• In animal skin, provitamin 7-dehydrocholesterol absorbs ultraviolet-B radiation ($290\text{--}315\text{ nm}$), which causes photolytic cleavage of the B-ring between carbon 9 and carbon 10, generating previtamin $D_3$.
• Previtamin $D_3$ undergoes spontaneous thermal isomerization to form cholecalciferol (vitamin $D_3$).
• During this rearrangement, an exocyclic methylene group is created with a double bond between carbon atoms 10 and 19 ($C_{10}=CH_2$).

Correct option: (3) 10 and 19