Question

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

1. It is an historical accident, of no mechanistic importance.
2. There were originally more than 27 tool monomers, but some have been 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 means that they must have an even number of monomers (2, 4, 6, etc).

15. When an organism has two copies of each piece of design information, we refer to this state by which of the following terms? (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 the gamete. This chromosome is chosen at random from the two copies this parent has – one received, in turn, from its father and one from its mother (the “grandparents” here). This process of choosing one of these two chromosomes is referred to specifically by which of the following technical terms?

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

Answer 1

14.Ans. (c) double-stranded nucleic acids (like DNA double helix ) wouldn't be stable with only three bases.

Explanation: There is stability in double stranded DNA molecule which has the genes. Stability is maintained by four complementary opposite base pairing between C and G, A and T i.e. between one purine and one pyrimidine. If only three bases were there, there would have not been such exactly compatible and opposite base pairing and hence wouldn't been stable.

15.Ans. (b) diploid

Explanation: Two are two sets of chromosomes in a diploid individual; one coming from mother and other set coming from father. Each h homolog of homologous chromosome pair contain allele for each gene ( sequence of nucleotides controlling traits/characters in organisms).

16.(c) independent assortment

Explanation: This involves random separation of genes independent of one another. One set of chromosomes contain one allele and another set of chromosome (homologous pair) contain one allele of a gene and these alleles get separated independent of one another at the time of gamete formation.