Final answer:
Species relativity is determined by comparing amino acid sequence homology among species, indicating their evolutionary kinship and distance. Sequence alignment tools and databases like GenBank are used to analyze sequence homology and three-dimensional protein structures for phylogenetic relationships.
Step-by-step explanation:
To determine species relativity based on amino acid sequence, scientists compare the amino acid sequence homology among different species. Evolutionary kinship can be assessed by measuring the similarities or differences among various species' DNA or protein sequences. By comparing these sequences, one can infer the evolutionary distance and common ancestry of different organisms. For example, identical amino acid sequences in human and chimpanzee cytochrome c suggest a very recent common ancestor. In contrast, significant differences between human and yeast cytochrome c amino acid sequences indicate a more distant common ancestor.
Sequence alignment tools allow researchers to align and analyze sequences to determine the percentage of sequence homology. Factors such as percentage conservation, trends in conserved amino acid types (apolar, polar, charged), and topological differences in the three-dimensional structures of proteins provide insight into evolutionary relationships. The conservation of certain protein folds, despite sequence dissimilarity, reflects evolutionary pressures to maintain functional structures.
Finally, when studying molecules like tRNAs, specific bases or combinations thereof can be predictive of the evolutionary history of genes. Computational tools and databases like GenBank aid in the analysis, providing a means to compare sequences from different species and to understand their phylogenetic relationships.