14-9.    Back in the good old days, virtually all mosquitoes were killed by DDT.  Nowadays, most mosquitos are resistant to the insecticide.  If we stop using DDT today and wait 10 years it is likely most mosquitos will again be sensitive.


A.  How did the mosquitoes become resistant?


B.  Why will they probably be sensitive 10 years from now?



14-10.   The order of genes on the Y chromosome was figured out a few years ago. In an article reporting the arrangement of genes on the Y chromosome, a researcher is quoted as saying "This is the first glimpse we have had that the human genome was thrown together with some forethought." I assume (hope?) the researcher meant it looks like it was thrown together with some forethought. Why, according to the theory of evolution by natural selection, should the genome appear to be "thrown together with some forethought" if it really got that way as a result of random mutations?



14-11.   Enzyme X is an essential enzyme containing 1 polypeptide 100 amino acids long.  You can isolate enzyme X from 10 different species of bacteria and compare the amino acid sequences.  You find that amino acids 14-49 are the same in all 10 species, but the remaining amino acids vary from one species to the next.


A.  Why are amino acids 14-49 always the same?  (Is there selection or no mutation or what?)


B.  Suppose you can sequence the part of the DNA coding for amino acids 14-49 in all 10 bacterial strains.  Will the DNA sequences be identical?



14-12.   You have 2 alleles of the same gene. You compare the proteins made by the two different alleles, then you compare the 2 DNA's of the two alleles themselves and finally you compare the cDNA's derived from the mRNA's made by the two different alleles.

The proteins coded for by the two alleles are very similar -- about 1% of the amino acids are different and the proteins are the same length. The cDNA's are less similar than the two proteins -- about 5% of the bases are different. If you compare the two alleles, they are even less similar -- about 15% of the bases are different.

The differences in the cDNA's are spread out, but many (although not all) of the differences are found in positions along the chain that are multiples of 3 bases apart, say at position 152, 167, 170, 290 etc. The differences in the genes are not spread out evenly -- some sections have lots of differences and some have only a few.


A. Why are the cDNA sequences more different than the protein (amino acid) differences, and why is there a pattern to where the variation occurs?


B. Why are the genes more different than the cDNA's?


C.  If you measure the mistakes made by DNA polymerase in a test tube, the enzyme makes mistakes at random and any base is equally likely to be altered. Why do differences tend to cluster in certain areas of the cDNA or genes (since DNA polymerase makes mistakes all over)?