Random mutations occur in DNA at a high frequency, although most are re paired q

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Random mutations occur in DNA at a high frequency, although most are re paired quickly and do not alter the DNA sequence in germ cells (sperm an egg cells). However, occasionally a DNA mutation will occur in the germ line and be passed on to the next generation through mating. Explain why most variations in DNA sequence between individuals of the same species are found outside of the protein-coding regions of genes. Explain how proteins encoded by paralogous genes can be less similar to each other in structure and function than corresponding proteins encoded by orthologous genes. The amino acid sequence of a protein determines its three-dimensional structure, which in turn determine its function. The amino acid sequences of the bacterial and mouse ribonucleotide reductase proteins shown Figure 1.30a are ~20% identical, and both proteins the same structure and function. Moreover, the

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7. The mutations occur randomly in nature. The mutations which occur in the DNA sequence during replication and during stresses conditions are repaired to the maximum extent. Some of the mutations survive and get passed on to next generation. The mutations which occur in the coding region of a gene, if not repaired will alter the activity of the respective protein and many such mutations can alter the phenotype of the organism. The organism is constantly under natural selection. Any such mutation which reduces the fitness of an organism is dangerous for the species. Hence such mutants get eliminated in the due course of time. But if the mutation has occurred in the noncoding part of the genome, then it is likely that such mutations remain in the population; because noncoding mutations do not directly alter any protein structure nor the phenotype. Hence its chance of getting eliminated by natural selection is far less as compared to mutations in the coding region. Hence we find more variation in the noncoding region among individuals of same species.

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