U4 AOS2 Topic 8: Phylogenetic Tree and Relatedness

Structural morphology is the study of physical structures to establish relatedness.

Features that are present in more than one species and they may look different and function differently, but they are derived from a common ancestor, this is known as the homologous structures.

Divergent evolution is the process in which a common ancestor evolves into more than one descendant species.

Analogous structures features present in more than one species with the same function but they are not originated from a common ancestor.

convergent evolution the process in which distantly related species evolve similar traits over time

vestigial structures features that have lost all or most of their usefulness as a result of evolution one example of this is the tail bone found in humans which serves no major purpose.

Study of the similarities between organisms at a DNA and amino acid level is known as molecular homology

Genes that have remained largely unchanged throughout evolution and are found across many different species are known as conserved genes

Haemoglobin (Hb) plays an important role in carrying oxygen from the lungs to the cells around the body of many different species. It is composed of up to 4 polypeptide chains: 2 alpha chains and 2 beta chains, both these chains include amino acids and researchers assess the difference in the number of amino acids to study the relatedness of organisms.

Cytochrome can enzyme found in mitochondria that carries electrons in aerobic and anaerobic respiration reactions

Mitochondrial DNA (mtDNA) circular DNA found in mitochondria

As with amino acid sequences, DNA sequences can also be used to determine the relatedness between different organisms.

DNA a double-stranded nucleic acid chain made up of nucleotides, which carries the instruction for the organisms functioning.

Nucleotides have different nitrogenous bases – adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U).

Genome the complete set of DNA housed within an organism

Nuclear DNA DNA that is located in the nucleus of a cell

 

A limitation of using amino acids to analyse the relatedness of organisms is that for closely related species sequences are likely to be very similar for certain proteins. In these instances, scientists determine relatedness by comparing nucleotide sequences.

We can also compare whole genomes of different species, the more similar the genomes, the more closely related the species are.

 

Phylogenetics is the study of relatedness between organisms, a diagram that we use to show the relatedness between organisms is known as phylogenetic tree.

A direct sequence of species evolved from a common ancestor is known as lineage.

Taxon (pl. taxa) is a group into which related organisms are classified; these are arranged in a order from kingdom down to the species. 

The phylogenetic tree shows us the relatedness between taxa, the timeline of different lineages, and shared characteristics of different taxa.

We can read phylogenetic trees backwards to determine the most closely related species to a particular taxon.

Now let’s look at a few different components of a phylogenetic tree,

Root represents the most recent common ancestor, Branch each line on the phylogenetic tree that represents an evolutionary path, Node a point where the branches split from each other, and Leaf that shows the final form of specie.

To construct a phylogenetic tree, we need to follow a few steps, we will first find the most common trait between largest number of animals such as them having four legs, then we will look at the most common trait between the remaining animals and we will keep progressing like this branching out animals that don’t have common traits until we come to a conclusion.

Dating techniques are not always completely accurate and fossils are not typically perfectly preserved, in this case we can use phylogenetic trees to express these uncertainties. Adaptive radiation is when a single species evolves into many different forms.