14. Contemporary organisms on planet earth encode their designinformation using nucleic acids polymers that have fourdifferent monomers. These monomers are read three at a time toproduce tool polymers – made up of a different kind of monomer.[This is a straightforward case of combinatorial coding ofinformation.] This means that the number of different monomers inthe tool polymer could, in principle, be 64. In practice,this number is actually 20 – because different nucleic acid monomertriplets (called “codons”) are read as NOT different. [Such codonsthat are not distinguished from one another are said to be“degenerate”.] If nucleic acids had three differentmonomers instead of four, triplet codons could encode 27 differenttool monomer units, in principle. This would be plenty of codingcapacity for the 20 different tool monomers that are actually used.In view of this, which of the following is the most likelyexplanation for the fact that contemporary organisms use four NOTthree nucleic acid monomers?

1. It is an historical accident, of no mechanisticimportance.
2. There were originally more than 27 tool monomers, but some havebeen lost in the evolution of contemporary organisms.
3. Double stranded nucleic acids (like the DNA double helix)wouldn’t be stable with only three different bases.
4. The requirement that nucleic acids replicate themselves meansthat they must have an even number of monomers (2, 4, 6, etc).

15. When an organism has two copies of each piece of designinformation, we refer to this state by which of the followingterms? (Choose the most specific term.)

1. haploid
2. diploid
3. asexual
4. somatic

16. When an adult sexual organism (“parent” here) makes a gamete(egg or sperm) she/he places one copy of each chromosome into thegamete. This chromosome is chosen at random from the two copiesthis parent has – one received, in turn, from its father and onefrom its mother (the “grandparents” here). This process of choosingone of these two chromosomes is referred to specifically by whichof the following technical terms?

1. crossing over
2. recombination
3. independent assortment
4. random mating