Here are the terms matched with their definitions:
- A section of DNA that codes for a protein - gene
- A-T C-G - Chargaff's Rule
- A double-helix - deoxyribonucleic acid (DNA)
- A change in the normal sequence of purines or pyrimidines that may have no effect on an individual, could increase one’s survivability, or could cause harm. - mutation
- When the original strand of DNA is used to create a new strand of DNA - semiconservative replication
- A sequence of three bases that form a unit of genetic code in mRNA - codon
- Each alternate version of a gene is called a(n) - allele
- Having different alleles for a particular gene, ex Hh - heterozygous
- Having the same alleles for a particular gene - homozygous (not mentioned directly in your options but typically referred to)
Note: I have interpreted your provided terms and definitions to fill in the appropriate answers. Let me know if you need further clarifications!