Evolution is the change in characteristics of certain species over generations. Evolution keeps living things here on earth as they adapt to their physical environment based on natural selection.
With the mention of the vertebrate genome, the five classes of vertebrates come to mind, namely mammals, fish, reptiles, amphibians, and birds. The common characteristic in the vertebrates or phylum Chordata is they all have a backbone.
Vertebrate genome evolution began over 500 million years ago during the Cambrian explosion, whereby two genomes duplicated successively in a marine chordate lineage leading to a common origin of vertebrates. With the help of science, you can conduct experiments to understand development architecture and the impact of genome duplications on vertebrate anatomy.
Vertebrates are classified as a clade, meaning they have a common ancestor. Because the genesis of the clade is intertwined with the deeper sections of our evolutionary past, it should come as no surprise that the origin has different theories by anatomists, physiologists, embryologists, and paleontologists.
However, their common aim is to understand the relationship among the vertebrates and uncover their origin and evolution.
Some of the studies that support the evolution of vertebrates include:
Based on ChIP-seq and Chromatin Accessibility
ChIP-seq and chromatin accessibility is the level of physical compaction formed by DNA to identify functional similar cis in species. Following the Cambrian radiation, the architecture of the vertebrate body had an equivalent blueprint. The structures consisted of an axial notochord, ventral heart, pharyngeal gill slits, and a dorsal neural tube.
Studies suggest that the evolution was possible following the presence of specific cells like neural crest and ectodermal placodes. The vertebrates evolved with predatory jaws, a complex brain, sharper sensory organs, and an endoskeleton which enables the active predation lifestyle.
In addition, the sensory organs of the peripheral and central nervous system include the inner ear, nasal organs, eyes, and the lateral line in fish that makes them streamlined.
The 2R hypothesis suggests that vertebrates underwent two whole-genome duplications (WGD) related to the evolution of vertebrates. The theory further argued that on numerous occasions of gene duplication and sub-functionalization of duplicated gene copies serve as elements for the genesis of the evolutionary advances found in invertebrates.
However, some scientists oppose the 2R hypothesis arguing that anatomical analysis of vertebrate fossils is not enough to link the evolution based on WDG and chromatin accessibility.
Further, while there is morphological diversity in adult animals, as compared to embryonic forms, there is a significant reduction in variability.
Following this observation, the embryologist Ernst Von Baer developed the ‘Laws of Development,’ which explains organisms’ progress through acquiring first the most general traits of the clade to which they belong, and then the specific features of their respective species.
Based on the One-to-Four (-to-eight in fish) Rule
Vertebrate evolution is possible because of gene and genome duplications, as they provide a source of DNA for selection, mutation, and drift.
A growing body of evidence suggests that throughout the development of vertebrates from early deuterostome ancestors, whole genomes underwent two rounds of duplication (one-two-four Rule), leading to the modern appearance.
The second genome duplication is suggested to have occurred during the early Devonian period. However, recent evidence indicates that the fish genome was duplicated a third time later in the Devonian period, producing up to eight copies of the original deuterostome genome.
Based on Chromosome Evolution
Science can prove the evolution of vertebrates from their origin using DNA sequences and the evolution of chromosomes through the rebuilding of the order of genes from an ancient Amniota genome that is 326 million years old. Using duplicated chromosomes from the Amniota genome, you can create a list of duplicated genes resulting from the two whole-genome duplications (WGD).
Fusion took place following the divergence of the lineage of Gnathostomata (jawed vertebrates) from Cyclostomata (extant jawless fish), resulting in the formation of the primordial Euteleostomi (bony vertebrates) genome, which included 50 chromosomes.
Vertebrate Genome Evolution
Jawless fish were among the earliest vertebrates, and they lived about 600 million years ago. The jawless fish had a cranium without a vertebral column. The phylogenic tree gives an overview of the vertebrate evolution with jawless fish, cartilaginous fish, bony fish, amphibians, reptiles, birds, and mammals.
On the evolution of fish, the first hagfish developed a partial vertebral column. Then, about 450 million years ago, fish with a complete vertebral column made an appearance.
These fish possessed jaws as well and were possibly related to extant sharks. A bony skeleton would be able to support the enormous body weight. Ray-finned and lob-finned fish are descendants of the first bony fish that existed.
The evolution of the other vertebrates took place after the evolution of fish. It involved;
- For the amphibians, they evolved from lobe-finned fish ancestor approximately 365 million years ago. They were the first vertebrate to dwell on land like the apes, but they had to return to the water to reproduce. Reproduction necessitated the need for them to live near water bodies.
- Reptiles descended from amphibians at least 300 million years ago. When reproducing, they produced amniotic eggs, which were then fertilized internally. They were the first vertebrates to breed without the need to return to the water and might potentially live almost anyplace.
- Mammals and birds descended from reptile-like predecessors at some point in their evolution. According to fossil evidence, the earliest mammals appeared approximately 200 million years ago, and the earliest birds appeared roughly 150 million years ago.
Genome Evolution Explained
Before the evolution of vertebrates, they were mammals, and birds were ectothermic. Ectothermy is the ability to control body temperature from outside in relation to behavior. For example, when it’s hot and sunny, an ectotherm will find shade to keep cool. In addition, their metabolic rate is influenced by external temperatures.
Mammals and birds evolved to endothermy. Endothermy is the ability to control body temperatures from inside the body based on metabolic and physical processes.
For example, on a chilly day, an endotherm will produce extra heat by increasing its metabolic rate, which will help it stay warm. On a hot day, the animals will expel the excess heat by increasing blood flow to the skin’s surface.
Keeping the body’s temperature consistent permits cells to operate at peak efficiency. In addition, with consistent temperatures, the animal maintains a high metabolic rate and physical activity level regardless of the external temperatures. Maintaining a constant body temperature demands more energy and food.
During the Mesozoic era, Parareptilia and synapsid amniotes were abundant. The bony fishes took over as the main species in the sea.
The birds first appeared during the Jurassic period, and they were derived from a dinosaur known as Paraves.
In the late Triassic Period, therapsid amniotes evolved into mammals as a result of the evolution and the mammals spread across the world.
Experiment on Gene Families in Fugu and Humans
It is possible to conduct science experiments to identify gene families in Fugu and humans or other vertebrates. Fugu or pufferfish is seven times smaller than the human genome but contains a similar amount of genes. Thus, the use of Fugu in genome sequencing is a potent and cost-effective technique for predicting gene order in the human genome and elucidating the structure of human genes, particularly for large-scale projects.
Materials required for the experiment include;
- Fugu scaffolds
- Predicted protein sequences from the human genome
- Protein-protein BLAST
- Drosophila or Ciona sequences
Phylogenetic trees of larger gene families are not included in the experiment since they frequently provide difficulties in sequence building—instead, only families with two-ten paralogous genes. Following the identification of the various gene families, the generation of alignments with the CLUSTALW 1.82 program.
When experimenting, the sequences with a gap of more than 10% is deleted from the dataset. The deletion helps reduce the likelihood of including misaligned amino acids in the alignment. In addition, remove all positions in the alignment left or right of the gap until you find a column in the sequence alignment which conserves the residues across all the genes included in the analysis.
After that, a medium value is determined using the other values. Only alignments preserved for phylogenetic analysis are those with over 50 alignments. Phylogenetic relationships divide the animals into ranks and illustrate the relationships between species in the form of a phylogenetic tree.
In conclusion, the Cambrian explosion led to an increase in the diversity of organisms. Vertebrates appeared about 500 million years ago, with Myllokunmingia as the oldest known vertebrate species. The vertebrate anatomy included a notochord, primitive vertebrae, and a delineated head and tail during the Cambrian period.
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At Modern Biology Inc, we offer high-quality educational materials and activities to assist students and instructors in learning about the evolution of the vertebrate genome and other key science topics. Although scientists have long disagreed over the giant panda’s taxonomic classification, new DNA hybridization tests clearly indicate that this species is more closely linked to bears than to raccoons.
These crucial principles are shown in our experiment, in which students compare DNA sequences from salmon, turkey, chicken, and cow using a dot-blot hybridization technique.
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