How do scientists use protein sequences or DNA to construct cladograms? How do they find relationships between animals?
Scientists use protein sequences or DNA to construct cladograms, which are diagrams that depict the evolutionary relationships between different species or groups of organisms. These diagrams are based on the idea that species that share more similarities in their protein sequences or DNA are more closely related.
To construct cladograms, scientists follow a series of steps:
1. Obtaining and aligning protein sequences or DNA: First, scientists obtain protein sequences or DNA from different species. This can be done through various techniques, such as extracting DNA from tissue samples or retrieving protein sequences from databases. Once obtained, the sequences are aligned to ensure that corresponding regions are matched up accurately.
2. Determining genetic distances: Scientists then calculate the genetic distances between each pair of species. This is done by comparing the protein sequences or DNA and quantifying the differences. The genetic distance can be measured in terms of the number of nucleotide or amino acid substitutions required to transform one sequence into another.
3. Constructing a distance matrix: The genetic distances are then used to create a distance matrix, which is a table that shows the pairwise similarities between all pairs of species. This matrix helps in visualizing the genetic relationships between species.
4. Creating a tree using various algorithms: Scientists employ various algorithms to create a tree, also known as a phylogenetic tree or cladogram, based on the distance matrix. One widely used algorithm is the neighbor-joining method, which constructs a tree by iteratively grouping the closest species together based on their genetic distances.
5. Adding branch lengths: Once the tree is constructed, scientists add branch lengths to represent the genetic distances between the species. Longer branches indicate greater genetic differences, while shorter branches represent closer relationships.
By using these techniques, scientists can determine the evolutionary relationships and find similarities between different animals or organisms. These cladograms help in understanding the evolutionary history, common ancestors, and divergence of species over time.