A3.2 Classifications and cladistics Flashcards

Question

In a cladogram how do you know which two organisms are more closely related?

Answer 1

In cladograms, closer two organisms are in evolutionary terms, more derived characteristics they share. This means their common ancestor is more recent.

Answer 2

Node = branching point from ancestral pop in a cladogram. It represents a speciation event.

Answer 3

Terminal branch = indicates both extinct & extant species in a cladogram, leading to a terminal node.

Answer 4

Terminal node = represents hypothetical last common ancestral interbreeding pop of taxon labelled at a tip of a cladogram.

Answer 5

Root = central trunk of a cladogram, indicating common ancestor to all groups that branch from it.

Answer 6

Figworts were considered to be 8th largest family of flowering plants (angiosperms), containing 275 diff genera. Biologists have been classifying plants using external features (morphology) for many yrs. If these features are similar assumption is that plants are closely related, & that they share many genes. Genotype actually does influence phenotype, so this makes logical sense.

Answer 7

However, many of figwort plants were too dissimilar in morphology to function as a meaningful grouping. Taxonomists examined genes for chloroplasts in figworts & decided to split the figwort species into five diff clades. Now less than half of species remain in figwort family – which is now 36th largest among angiosperms.

Answer 8

New methods of analysis are providing evidence for reclassification of figwort family. In this method, a few genes are sequenced & their base sequences are compared to those of similar organisms. This allows reclassification to happen as is case with figwort family.

Answer 9

Classification of all organisms into three domains can use evidence from rRNA base sequences. This reclassification adding the extra taxonomic level 'domain' above kingdoms was proposed in 1977 by Carl Woese.

Answer 10

Classification uses info available to group organisms together. In time of Carl Linneus often this evidence was taken from morphological features. This can align with evolutionary pathways if right features are used, but DNA sequences or amino acid sequences have improved evidence available & have supported development of cladistics. Carl Woese was one of 1st to use DNA sequences & this revolutionised the tree of life.

Answer 11

Single celled organisms have been classified into Eukaryotes (with a membrane bound nucleus) & Prokaryotic Cells (without a nucleus). For a long time shape of prokaryotes was used to classify them.

Answer 12

A prokaryote is a simple, single-celled (unicellular) organism that lacks an organized nucleus or any other membrane-bound organelle. Prokaryotic DNA is found in a central part of the cell: nucleoid. With today's DNA sequencing technology it seems like a logical idea to try to use part of this DNA to make comparisons between diff species of bacteria. Carl Woese was working in 1970's, 30 yrs before human genome project & development of rapid DNA sequencing techniques. He wanted to find a small gene which was present in all species, to achieve this task. All prokaryote cells have ribosomes. Ribosomes are made of ribosomal RNA. RNA is a molecule known to exist in earliest evolution of life on Earth

Answer 13

The prokaryotic small ribosomal subunit, or 30S subunit, is smaller subunit of 70S ribosome found in prokaryotes. It is a complex of 16S ribosomal RNA (rRNA) & 19 proteins. This complex is implicated in binding of transfer RNA to messenger RNA (mRNA). Small subunit is responsible for binding & reading of the mRNA during translation. Small subunit, both rRNA & its proteins, complexes with large 50S subunit to form 70S prokaryotic ribosome in prokaryotic cells. This 70S ribosome is then used to translate mRNA into proteins.

Answer 14

Carl Woese decided to explore diff in gene which codes for this 16S rRNA molecule found in ribosome small-subunit. It was a good choice, as it is just right length. Long enough to show diff between groups, but short enough to be sequenced using early technology available.

Answer 15

Woese’s approach was revolutionary bc comparisons of physical features are insufficient to differentiate between prokaryotes that appear fairly similar in observations. Comparison of DNA & RNA sequences provided Woese with a sensitive tool that revealed extensive variability of prokaryotes. RNA, which is transcribed from DNA, varies between organisms. This allowed Woese to suggest a new classification using rRNA base sequences. Pioneering work of American microbiologist Carl Woese in early 1970s has shown, however, that life on Earth has evolved along three lineages, now called domains—Bacteria, Archaea, & Eukarya. Woese defined Archaea as a new domain, & this resulted in a new taxonomic tree. Many organisms belonging to Archaea domain live under extreme conditions & are called extremophiles. To construct his tree, Woese used genetic relationships rather than similarities based on morphology (shape).

Answer 16

Classification of all organisms into three domains used evidence from rRNA base sequences. This reclassification adding the extra taxonomic level 'domain' above kingdoms was proposed in 1977.

Answer 17

A system of organising knowledge on all living things based upon their characteristics and more recently their DNA.

Answer 18

- It allows us to better organise and understand the world around us by grouping similar things or ideas. - It allows for better communication by providing a common language to discuss or refer to certain groups of things. - It allows us to be more efficient by being able to quickly and easily find and categorise things and information. - It allows for further research and analysis to identify patterns and trends to better understand the things we have classified and the systems and phenomena that are a part of them

Answer 19

The science of categorisation or classification.

Answer 20

A group of one or more populations of an organism or organisms seen by taxonomists to form a unit.

Answer 21

There are also many intermediate taxa, such as subfamilies & superorders, that have been added to account for complexities in relationships between diff groups. Shared characteristics used to place species into taxa were mostly morphological. In other words, organisms that looked most alike were most closely related

Answer 22

Traditional hierarchy of taxa poses some problems, however. These taxa are arbitrary & don't reflect complex evolution that has occurred over billions of years. Traditional way of grouping organisms doesn't always correspond to patterns of divergence generated by evolution.

Answer 23

We have shifted our perspective of the classification of life. From a system based on similarities in appearance and behaviour, to a more precise and detailed one. The latter is based on the use of genetic analysis to determine evolutionary relationships, specifically nucleic acid or amino acid sequences.

Answer 24

- It reflects evolutionary relationships among diff organisms, providing a natural & biologically meaningful way to group them in clades based on common ancestry. - It reflects process of evolution, such as branching patterns of speciation shown through cladistics & emergence of new features. - It can be used to make predictions about characteristics of organisms, e.g. their biochemistry or ecology, based on their evolutionary relationships. - It helps us to understand diversity of life on Earth by providing a context for evolution & distribution of diff organisms.

Answer 25

Genetic & molecular differences between organisms slowly increase over time as a result of evolution. The ‘molecular clock’ is name given to this technique of measuring the time since there was a common ancestor. Molecular clock can only provide estimates because mutation rates depend on a range of things. These include size of a population, selection pressures, genome size as well as a degree of randomness

Answer 26

The need for a calibration point in molecular clock analysis is an essential component. A calibration point is a period of time in which the precise moment at which two species diverged is known. As an example, the oldest fossil of a specific species that is known to exist can be used as a calibration point. The molecular clock can be used to calculate the divergence times of other species in reference to a calibration point once it has been established