The Dna

Friedrich Miescher discovered DNA in 1869, isolating "nuclein" from pus cell nuclei.

Key points:

• Watson and Crick: Discovered DNA's double-helix structure.
• Rosalind Franklin: Contributed to structural discovery via X-ray diffraction.
• Griffith: Demonstrated DNA as genetic material through transformation experiments.

Therefore, Friedrich Miescher is credited with the initial discovery of DNA.

The correct Option is : 3

Step 1: Griffith's experiment overview.
Frederick Griffith, in 1928, conducted experiments with two strains of Streptococcus pneumoniae

S-strain: Virulent, with a polysaccharide coat, causing disease.

R-strain: Non-virulent, lacking the polysaccharide coat.

Step 2: Discovery of the transforming principle.
Griffith observed that heat-killed S-strain bacteria, when mixed with live R-strain bacteria, could transform the R-strain into the virulent S-strain. This transformation indicated the presence of a "transforming principle" capable of transferring genetic information.

Step 3: Explanation of options.
Option (A): Incorrect. Proteins were later ruled out as the transforming principle by experiments conducted by Avery, MacLeod, and McCarty.

Option (B): Incorrect. The polysaccharide coat is not responsible for transformation but is a characteristic of the S-strain.

Option (C): Correct. The transforming principle is a substance (later identified as DNA) that can transfer genetic material from one bacterium to another.

Option (D): Incorrect. Lipids are not involved in bacterial transformation.

Step 4: Conclusion.
The transforming principle in Griffith's experiment was identified as a substance capable of transferring genetic material, which laid the foundation for the identification of DNA as the genetic material.

Step 1: Overview of Down syndrome.
Down syndrome is a genetic disorder caused by trisomy of chromosome 21. It is associated with a variety of physical, developmental, and physiological abnormalities.

Step 2: Characteristic symptoms.
Common symptoms of Down syndrome include Heart defects, such as heart murmurs. Flattened facial profile and upward slanting eyes. Intellectual disability and developmental delays.

Step 3: Analysis of options.
Option (A): Incorrect. Abnormal hair growth is not a characteristic symptom.

Option (B): Correct. Heart murmurs are commonly associated with congenital heart defects in individuals with Down syndrome.

Option (C): Incorrect. Skin rash is not a typical symptom.

Option (D): Incorrect. Eye color changes are unrelated to Down syndrome.