Phylogeny Flashcards
(13 cards)
Define phylogeny
The evolutionary relationships between all organisms and attempts to trace the evolutionary history of all life on Earth. It is based on the hypothesis that all living organisms share a common ancestry.
How old is the Earth compared to the oldest known fossil?
Earth is 4.6 billion years old, while the oldest fossil found is 3.5 billion years old (a fossil of a bacteria-like organism)
Why is microbial life so important in Earth’s history?
80% of life during the history of life has exclusively been microbial. It is still the dominant life form on Earth. It is estimated that the total number of microbial cells on Earth is 2.5E30, making it the major fraction of biomass. All other forms of organisms evolved from microbes.
How did the tree of life begin? Who came up with it and how did they imagine it?
In the 1700s, people began to categorize living organisms by visual observations. Carolus Linnaeus drew the initial tree of life, where he separated all living things he could see into either plant or animal. He then came up with further categories according to other visual cues such as size. Linnaeus established taxonomy.
How did the tree of life evolve in the mid 1850s?
Ernst Haeckel proposed four kingdoms of life, adding monera (all bacteria) and protists to the already proposed plant and animal kingdoms. He separated the prokaryotes from the eukaryotes, where the eukaryotes were the animals, plants, and the protists. Protists are all eukaryotic organisms that are not animals, plants, or fungi.
How did Robert Whittaker contribute to the tree of life?
He established five kingdoms of life and added fungi as a distinct branch of eukaryotes, as their appearance and behaviour differ drastically from protists. He drew a line between monera, which have no nucleus, and all other kingdoms. From this time onward, the nucleus was a defining feature (eukaryotes have nuclei while prokaryotes do not)
How were eukaryotes and prokaryotes named?
Comes from the work karyon, which is Greek for kernel or nut, because the microscopic appearance of a nucleus looks like a dark stained kernel or nut. Prokaryote means BEFORE the nucleus, while eukaryote means NEW nucleus.
How is a nucleus defined? What about a nucleoid?
Defined by a surrounding membrane and contains the primary genetic material of the cell. Prokaryotic cells concentrate DNA in a nucleoid. The DNA in the nucleoid is organized and condensed using proteins called nucleoid associated proteins (NAPs).
In the past, how was the tree of life categorized?
Subjectively (based on appearance) - it is open to interpretation (ex. different people have different ideas on what ‘large’ may mean), and is therefore biased and not reproducible
What exact feature is now used to assess evolutionary relatedness between organisms?
Scientists now compare organisms based on the fact-based analysis of protein and DNA sequences, which are present in all organisms. The most current understanding of the tree of life has evolved from research introduced by Carl Woese and George Fox in 1977. They chose to examine gene sequences that encodes small subunit ribosomal RNA of different organisms; since RNA is an essential gene, they hypothesized that it would be under great evolutionary pressure to resist change and mutations. They used the number of differences in DNA sequence of a particular ribosomal RNA gene to determine evolutionary relatedness, where fewer changes in sequence means that they are more closely related.
What is the hypothesis as to the origin of eukaryotic and prokaryotic cells?
Since all cells are similar in nature, it is thought that all cells come from a common ancestor, which was termed the “Last Universal Common Ancester” or LUCA; LUCA is located at the base of the tree
What did Woese and Fox discover?
They discovered that a certain type of bacteria (archaea) were significantly different from other type of bacteria and eukaryotes in terms of their nucleotide sequence. They proposed that the LUCA evolved into three different cell types, each representing a domain (archaea, bacteria, and eukarya). Archaea, despite lacking a nucleus, are more closely related to eukarya than to bacteria.
What do the branches on the tree of life represent?
The length of the branches represent time, while the distances between the lines represent evolutionary relatedness.
