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.
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DNA gene |
TAC |
AGC |
TTT |
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mRNA codon (No thymine in RNA!) |
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tRNA anticodon (No thymine in RNA!) |
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Amino acid Use the mRNA with the Genetic Code. |
Use the mRNA with the Genetic Code.
Answer the questions below.
Questions
- How many
nucleotides would be needed to code for a protein that has 100 amino acids?
- Using the Genetic Code in Table 6.3, write all of the possible codons that signal the start and end of a gene.
- Start:
- End:
- An amino acid sequence of a protein molecule includes methionine, lysine, serine and glycine. Show each different codon that could result in each of these amino acids. You will have more than one codon for all of them except methionine.
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Amino Acids |
All Possible Codons |
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Methionine |
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Lysine |
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Serine (Look carefully. There are six possibilities) |
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Glycine |
- Question 3 illustrates the redundant nature of the genetic code. Can you think of an advantage of having several codons that all code for the same amino acid?
- Procedure 6.3: Mutations. Read about mutations in this procedure. Fill in Table 6.4 to show the different outcomes for the defective cystic fibrosis gene.
Table 6.4: Outcome of mutation. Use the mRNA with the Genetic Code.
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A normal CF gene |
A defective CF gene |
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DNA |
TAA TAG AAA CCA CAA |
TAA TAA CCA CAA |
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mRNA codons (No thymine in RNA!) |
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tRNA anti-codons (No thymine in RNA!) |
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Amino acids (There should be 5 amino acids in the first column and 4 amino acids in the second column, one for each mRNA codon.) Use the mRNA with the Genetic Code. |
NOTE: The first amino acid is coded for twice—so you should write it twice.
Use the mRNA with the Genetic Code.
Answer the questions below.
Questions
- Examine the differences in the normal and defective CF gene (in the DNA).
- Is the mutation an addition, deletion, or substitution?
- Name the exact nucleotides that have changed in the DNA. (Nucleotides are the letters, A, T, C, or G)
- How did the changes in the DNA sequence affect the results of transcription and translation?
- Transcription, (i.e., what is different in the resulting mRNA?):
- Translation, (i.e., what is different in the resulting amino acids?):
- Read about cystic fibrosis in your lab book. How does this mutation affect the transmembrane protein that is involved in cystic fibrosis?
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