The codon shows how different combinations of mRNA nucleotides code for various amino acids what two amino acids are coded for by an mRNA segment reading GAG GAC

Glutamic acid and Aspartic acid.

Explanation:

Using the information obtained from a genetic code chart (an example can be seen in the attached image), the mRNA codon GAG translates to an amino acid named Glutamic acid while the mRNA GAC translates to an amino acid named Aspartic acid.

Hence, the two amino acids are coded for by an mRNA segment reading GAG GAC are Glutamic acid and Aspartic acid respectively.

1. The three boxers met at the gym. Simple subject is a part of the sentence which tells us who or what performs the action in a sentence. Simple predicate tells as what subject does in a sentence. I've put simple subject and simple predicate in this sentence in bold. The tree boxers is a subject, because it tells us who performed the action and tells us what the subject did.

2. Amy took her dog to the veterinarian. Amy is the simple subject because it tells us who did something in the sentence without and it doesn't include any modifiers, took is the simple predicate because it tells us what Amy did and it also doesn't include any modifiers.

3. Luke boarded the airplane. According to the rule mentioned in the first question, Luke is the simple subject because it answers the question who performed the action and there are no modifiers; boarded is the simple predicate which answers the question what the subject did and there are no modifiers.

4. Rachel redecorated her dining room. Rachel is the simple subject, because it tells us who redecorated the dining room; decorated is the simple predicate because it tells us what Rachel did and there are no modifiers. 

5. The lightning struck Bill’s house. The lightning is the simple subject because it answers the question what struck Bill's house; struck is the simple predicate because it answers the question what the lightning did to the Bill's house and there are no modifiers.