If CTT is the normal sequence of nucleotides on DNA, what is the resulting mRNA codon? What amino acid does this code for? When a point mutation changes the DNA sequence to CAT, how is the mRNA codon affected? What amino acid does this code for? What is T?

The normal DNA sequence CTT corresponds to the mRNA codon GAA. This is derived from the base pairing rules where C pairs with G and T pairs with A. The amino acid coded for by the mRNA codon GAA is glutamic acid.

When a point mutation occurs and the DNA sequence changes from CTT to CAT, the resulting mRNA codon becomes GUA. This happens because the base A in CAT pairs with U in the corresponding mRNA. The amino acid that GUA codes for is valine.

Regarding the last part of your question, T refers to thymine, one of the four nucleotides in DNA. It is not present in RNA, where uracil (U) replaces thymine. Therefore, in RNA, A will pair with U instead of T.