Questions about amino acids and their genetic codes, with partial answers

1.     When there are two codes for an amino acid, the two are either A or G, and C or U. They belong to the same groups. Why?

If it is purely due to randomness, this can’t be the case. There must be a reason for this. But what?

2.     Why some amino acids correspond to more codes than others?

It seems that amino acids with higher prevalence usually have more codes. An answer can be found at

https://www.reddit.com/r/askscience/comments/1ft19n/does_the_fact_that_some_amino_acids_have_multiple/

3.     It seems that for amino acids with multiple genetic codes, the differences in codes are concentrated on the last code of the three codes. Why?

One of the things that makes it possible is the third position of the codon. This is the position that is most likely to be variable. It’s often called the wobble position, as it the tRNA only reads the first two bases of the codon and balances, wobbling, on the third. I don’t know if this it true - somebody who knows more about tRNAs would have to tell you that.

Answer found at

https://www.quora.com/Why-do-some-amino-acids-have-more-than-one-codon-for-their-recognition?share=1

Reference:

Genetic code chart

https://www.genome.gov/genetics-glossary/Genetic-Code

Codon tables

https://en.wikipedia.org/wiki/DNA_and_RNA_codon_tables#Translation_table_1