Evidence of Evolution Flashcards
1
Q
Types of Evidence for the ‘Theory of Evolution’
A
- Fossil records
- Comparative anatomy
- embryology - comparing early embryonic stages of an organism’s development
- homologous organs - organs similar in structure but used differently
- vestigial organs - organs that were once important but have lost/changed their function
- Comparative biochemistry
- DNA
- mtDNA
- Protein Sequences
- Geographical Distribution of species
2
Q
Comparative Anatomy
A
- Comparing the structures of related animals to see the level of similarity between their functions
- Homologous organs are part of the anatomy that have a similar structure between different species even though they may have different functions
- The structural similarities between different species indicates a common evolutionary ancestor
3
Q
Comparative Anatomy - Forelimb
A
- An example is the arrangement of the forelimb in different species
- The differences would have arisen by natural selection over generations, as the limb became better adapted to its specific function
- Is it just a chance occurence that many animals have a similar forelimb structure; humerus, ulna, radius and similar carpal and metacarpal arrangement, or did they have a common ancestor at some stage in their evolutionary history?
4
Q
Vestigial Organs
A
- There are organs that have no apparent function and are reduced in size but are present and functional in other species
- Examples include our appendix, coccyx, abdominal separation (which forms the 6 pack), muscles to wriggle ears, body hair and others. There is no selection advantage or disadvantage to these features but they still exist in our population.
- This again suggests a common ancestor with a well-developed version of the vestigial organ
- As different selection pressures acted on the species, divergence would’ve occured
- This resulted in one population no longer needing the function of this organ so it becomes reduced in size and function
5
Q
Comparative Embryology
A
- If we compare the developing embryos in a variety of animals, they looks surprisingly similar at various stages
- At early development, we are almost identical to a fish with gill pouches, there is no advantage in this, so why does it happen?
- It most likely indicates a common aquatic ancestor
- In uhmans, one of the gill slits develop into the Eustachian tube. The other slits develop in thyroid gland and tissues.
- The more closely related the species are, the longer the embryos remain looking similar
- Is it just chance that almost all vertebrates follow a very similar development pattern?
6
Q
Comparative Biochemistry
A
- We are able to compare the DNA of animals with each other
- The more similar the DNA, the more closely related the animals are
- The advancement of technology now allows comparative studies to be coducted on DNA, mtDNA and proteins
- This is a very strong indicator that the animals must have a common ancestor
DNA Studies
- Similarities in DNA that can indicate closeness of species:
- Number of chromosomes
- Base sequence of genes/DNA strand
- Locations and numbers of Endogenous Retroviruses (ERVs)
- The less difference in the base sequence, the more closely related 2 species are and the more recent their common ancestor
7
Q
Comparative Proteins
A
- Long chains of amino acids make proteins
- Animals that are more closely related have many similar or identical protein chains
8
Q
Ubiquitous Protein
A
- Ubiquitous proteins are those found in all species which makes them useful for comparison
- The greater the differences in the amino acid sequence (due to mutation) that makes up the ubiquitous protein, the further back the common ancestor and the less closely related the species are
- E.g. Cytochrome C protein (table 17.3)
9
Q
Geographical Distribution
A
- Indicates migration patterns and patterns of evolution
- Species living in areas that are close often show similarities, suggesting a common ancestor species migrated from one area to another
- The more divergence between species indicates when the migration happened and how different selection pressures resulted in speciation
10
Q
Phylogenetic Tree of Life
A
- Evolutionary Tree - shows the inferred evolutionary relationships among various species based upon similarities and differences in their physical or genetic characteristics
- The taxa joined together in the tree are implied to have descended from a common ancestor
- A Divergent evolution - species have diverged from a common ancestor
- this is usually a result of isolated environmens, which blocks the gene flow among the distinct populations, allowing changes to allele frequency through genetic drift and natural selection
11
Q
Comparative Anatomy - Anthropoids
A
- Anthropoids (human-like primates) show many anatomical resemblances
- E.g. a gorilla and a human - high degree of similarity in structures and muscles. This indicates a common ancestor and that these species were closely related.
12
Q
Comparative Biochemistry - DNA Base Sequence
A
- Comparing base sequences in DNA
- All living organisms use the same DNA code
- Similarities in base sequences of DNA provide evidence for evolution, suggesting a common ancestor
- Species sharing a greater proportion of DNA = more closely related
- Species showing more differences in their DNA = more distantly related
- After speciation, differences would accumulate due to mutations, and processes, including natural selection or genetic drift
13
Q
Comparative Biochemistry - Comparing the number of chromosomes
A
- Comparing the number of chromosomes
- Species closely related have similar numbers of chromosomes
- E.g. horses - 32 homolgous pairs, donkeys - 31 pairs
- Humans - 23 pairs, Chimpanzee - 24 pairs
- However - it is imporant to note that because species have similar number of chromosomes it does NOT mean they are closely related e.g. potato plants have 24 pairs of chromosomes
14
Q
Comparative Biochemistry - comparing location and numbers of ERVs
A
- Compare the base sequences of ‘junk DNA’ (non-coding DNA) such as endogenous retroviruses (ERVs)
- ERVs are viruses that appear at specific locations in chromosomes
How?
- A retrovirus copies its RNA into the DNA of a host cell = reverse transcription
- The DNA is then inserted into a chromosome of the host cell
- If this DNA is inserted into gametes then the offspring will inherit this DNA. This make it an endogenous RV.
- The offspring will then have a copy of the ERV in the same place, in the same chromosome, in every cell
- All subsequent generations will also have a copy of the same ERVs in the same place in their genomes
- The more ERV’s in common, the more closely related the species are
- It has been observed that chimpanzees and humans have the same ERV’s located across several chromosomes indicating a common ancestor
15
Q
Comparative Biochemistry - mtDNA
A
- Comparing mitochondrial DNA (mtDNA)
- trace lineage through female line as inherit mtDNA from our mothers
- mtDNA mutates faster than nuclear DNA. So divergence from ancestors happens within a few generations.
- the amount of mutation is roughly proportional to the amount of time that has passed
- AND SO - scientists can use similarity of mtDNA to provide an estimate of a closeness of relationship through maternal ancestors
- If mtDNA is identical - they are closely related, even siblings
- If mtDNA is very different - not so closely related
- Useful in tracing migration pathways of humans out of Africa and the order in which humans spread across the globe
- There are only 37 genes in mitochondrial DNA and so they are easier to identify (info from booklet)
