Chapter 2, Problem 31P

Considering the yellow and green pea color phenotypes studied by Gregor Mendel:

a.	What is the biochemical function of the protein that is specified by the gene responsible for the pea color phenotype?
b.	A null allele of a gene is an allele that does not specify any of the biochemical function that the gene normally provides. Of the two alleles Y and y, which is more likely to be a null allele?
c.	In terms of the underlying biochemistry, why is the Y allele dominant to the y allele?
d.	Why are peas that are yy homozygotes green?
e.	The amount of the protein specified by a gene is roughly proportional to the number of functional copies of the gene carried by a cell or individual. What do the phenotypes of YY homozygotes, Yy heterozygotes, and yy homozygotes tell us about the amount of the Sgr enzyme (the product of the pea color gene) needed to produce a yellow color?
f.	The Sgr enzyme is not needed for the survival of a pea plant, but the genomes of organisms contain many so-called essential genes needed for an individual’s survival. For such genes, heterozygotes for the normal allele and the null allele survive, but individuals homozygous for the null allele die soon after the male and female gametes, each with a null allele, come together at fertilization. In light of your answer to part (e), what does this fact tell you about the advantage to an organism of having two copies of their genes?
g.	Do you think that a single pea pod could contain peas with different phenotypes? Explain.
h.	Do you think that a pea pod could be of one color (say, green) while the peas within the pod could be of a different color (say, yellow)? Explain.