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.
You wish to find the cis-acting regulatory DNA elements responsible for the transcriptional responses of
two genes, c-fos and globin. Transcription of the c-fos
gene is activated in response to fibroblast growth factor
(FGF), but it is inhibited by cortisol (Cort). On the other hand, transcription of the globin gene is not affected
by either FGF or cortisol, but it is stimulated by the
hormone erythropoietin (EP). To find the cis-acting
regulatory DNA elements responsible for these transcriptional responses, you use the following clones of
the c-fos and globin genes, as well as two “hybrid” combinations (fusion genes), as shown in the diagram below. The letter A represents the intact c-fos gene, D
represents the intact globin gene, and B and C represent the c-fos–globin gene fusions. The c-fos and globin
exons (E) and introns (I) are numbered. For example,
E3(f) is the third exon of the c-fos gene and I2(g) is the
second intron of the globin gene. (These labels are provided to help you make your answer clear.) The transcription start sites (black arrows) and polyadenylation
sites (red arrows) are indicatedYou introduce all four of these clones simultaneously into
tissue-culture cells and then stimulate individual aliquots
of these cells with one of the three factors. Gel analysis of
the RNA isolated from the cells gives the following resultsThe levels of transcripts produced from the introduced
genes in response to various treatments are shown; the
intensity of these bands is proportional to the amount of
transcript made from a particular clone. (The failure of a
band to appear indicates that the level of transcript is
undetectable.)
a. Where is the DNA element that permits activation
by FGF?
b. Where is the DNA element that permits repression
by Cort?
c. Where is the DNA element that permits induction by
EP? Explain your answer.
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