Question

why DNA is a genetic material cannot be RNA in human beings. and why RNA is a genetic material in other organisms.

Answer 1

Because DNA is chemically stable and RNA is not. A solution of DNA in salt water will not degrade substantially in 1000 years, let alone a lifetime. An equivalent solution of RNA will degrade substantially in a few days. This is because the extra hydroxyl group in RNA is, by far, the most reactive part of RNA and it isn't present in DNA. Other organusm have such tyoe of phusiology fir RNA