Consider statements about genetics: 1. A gene is a segment of DNA that codes for a protein. 2. Alleles are alternative forms of a gene. 3. The phenotype is the genetic makeup of an organism. Which are correct? MCQ with Answer and Explanation

Explanation:
Frederick Sanger determined the amino acid sequence of insulin in 1955, showing proteins have a specific sequence. Banting and Best isolated insulin, Hodgkin determined its 3D structure.

Explanation:
PCR involves repeated cycles of high-temperature denaturation (around 94°C) to separate the DNA strands. Normal DNA polymerases would be destroyed at these temperatures. Therefore, a thermostable DNA polymerase is required. Taq polymerase, isolated from the thermophilic bacterium Thermus aquaticus found in hot springs, is the most commonly used enzyme because it can withstand the high denaturation temperatures without losing its activity, eliminating the need to add fresh enzyme after each cycle.

Explanation:
The 'ozone hole' is a severe, seasonal thinning of the stratospheric ozone layer that occurs most prominently over the Antarctic region during the Southern Hemisphere's spring (September to November). This is due to the unique meteorological conditions in the Antarctic stratosphere, including the formation of Polar Stratospheric Clouds (PSCs) during the dark, cold winter, which provide surfaces for chemical reactions that release active chlorine from CFCs, rapidly destroying ozone when sunlight returns.