The symbols a, b, and c in the table below represent theE. coli lac system genes for the repressor (I ), the operator(O) region, and the β-galactosidase (Z), although notnecessarily in that order. Furthermore, the order inwhich the symbols are written in the genotypes is notnecessarily the actual sequence in the lac operon.Activity (+) or inactivity (−) of Z geneGenotype Inducer absent Inducer presenta- b+ c+ + +a+ b+ c- + +a+ b- c- - a+ b- c+/a- b+ c- + +a+ b+ c+/a- b- c- - +a+ b+ c-/a- b- c+ - +a- b+ c+/a+ b- c- + +a. Which symbol (a, b, or c) represents each of the lacgenes I, O, and Z ?b. In the table, a superscript minus sign on a gene symbolmerely indicates a mutant, but some mutant behaviorsin this system are given special mutant designations.Using the conventional gene symbols for the lac operon,designate each genotype in the table.
Gene Interactions
When the expression of a single trait is influenced by two or more different non-allelic genes, it is termed as genetic interaction. According to Mendel's law of inheritance, each gene functions in its own way and does not depend on the function of another gene, i.e., a single gene controls each of seven characteristics considered, but the complex contribution of many different genes determine many traits of an organism.
Gene Expression
Gene expression is a process by which the instructions present in deoxyribonucleic acid (DNA) are converted into useful molecules such as proteins, and functional messenger ribonucleic (mRNA) molecules in the case of non-protein-coding genes.
The symbols a, b, and c in the table below represent the
E. coli lac system genes for the repressor (I ), the operator
(O) region, and the β-galactosidase (Z), although not
necessarily in that order. Furthermore, the order in
which the symbols are written in the genotypes is not
necessarily the actual sequence in the lac operon.
Activity (+) or inactivity (−) of Z gene
Genotype Inducer absent Inducer present
a- b+ c+ + +
a+ b+ c- + +
a+ b- c- - a+ b- c+/a- b+ c- + +
a+ b+ c+/a- b- c- - +
a+ b+ c-/a- b- c+ - +
a- b+ c+/a+ b- c- + +
a. Which symbol (a, b, or c) represents each of the lac
genes I, O, and Z ?
b. In the table, a superscript minus sign on a gene symbol
merely indicates a mutant, but some mutant behaviors
in this system are given special mutant designations.
Using the conventional gene symbols for the lac operon,
designate each genotype in the table.
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