10.4 - Investigating diversity Flashcards
How do we investigate diversity when comparing observable characteristics
- old method — form of artificial classification (looking at anatomical features)
- based on the fact that each observable characteristic is determined by a gene(s) (with environmental influences)
- the variety within a characteristic depends on the number and variety of alleles of that gene (plus environmental influences)
What are the limitations with comparison of observable characteristics
- large number of characteristics are coded for by more than one gene. Instead the characteristics are phylogenic (means they’re not discrete from one another but rather vary continuously)
- often difficult to distinguish 1 from another, and characteristics may be modified by the environment
- therefore differences may be due to the environmental conditions and not the different alleles
- e.g. height being affected by genes, but also environmental factors like diet
Because inferring DNA differences by comparing observable characteristics has its limitations, what has replaced it
- inferring DNA differences by DIRECTLY OBSERVING DNA SEQUENCES
- this has been made possible through advances in gene technology made over recent years
Describe how comparison of DNA base sequences is done
- computerised systems will tag each nucleotide with a different colour fluorescent dye
- green = A, red = T, blue = C, yellow = G
- through sampling a member of a species’s DNA, we can sequence it to produce a pattern of coloured bands
- by analysing these patterns with scans via lasers, and interpreting these scans with computers, we are able to compare one species with another in order to determine how diverse they are
—> this technique can also be used to determine the evolutionary relationships between species (phylogenetic evidence)
Why is DNA sequencing able to tell us about a species’ evolutionary relationships
- when 1 species gives rise to another during evolution, the DNA of the new species will initially be very similar to that of the species that gave rise to it
- due to mutations, the sequences of nucleotide bases in the DNA of the new species will change
- over time, the new species will acquire more and more over time —> more differences in DNA
- therefore we expect that the more closely related = the more similarity in their DNA
Describe comparison of the base sequences of mRNA
- mRNA is coded for by DNA
- the base sequences on mRNA are complementary to those of the strand of DNA from which they were made
- we can therefore measure DNA diversity and therefore genetic diversity by comparing the base sequence of mRNA
Describe comparison of amino acid sequence in proteins
- sequence of amino acids is determined by mRNA, which is determined by DNA
- therefore we can measure genetic diversity by comparing the amino acid sequence of their proteins
- the degree of similarity will in turn reflect the degree to how closely related they are
Chimpanzee, gorilla, orang-utan, lemur, gibbon
The chimpanzee and the gorilla because they both show the same % precipitation (95%)
- The gibbon because it shows only a 3% difference (85-82) in precipitation between itself and the orang-utan
- all other primates show a greater difference
- these data suggest that the gibbon is much more closely related to humans than the lemur
- the haemoglobin study suggested the lemur was a closer relative
- the chimpanzee is shown to be most closely related to humans in the haemoglobin study, while in the gene bases study it is the gorilla
- there are fewer differences between the bases in the gene of a human and that of an orangutan 🦧 (29) then there are between the genes of a human and a lemur (48)
- this suggests that the evolution of humans and lemurs diverged earlier than that of humans and orangutans, giving more time for the amino acid differences to occur
- No
- the study suggests that gorillas (with fewer base differences) are more closely related to humans than chimpanzees
- the other studies suggest chimpanzees are more closely related to humans
- the position of the orangutan is the same in all 3 studies
- the position of the lemur is the same as in the immunological study but different from that in the haemoglobin study
What are Analogous characteristics
- arise from convergent evolutions
- when unrelated organisms develop similar structures which perform the same job
- these species are different in anatomical structure because they all have different evolutionary origin
- e.g. wings of a butterfly and wings of a pterodactyl
What are homologous characteristics
- arise from divergent evolutions
- they come from similar evolutionary origins and so will share the same basic anatomical structure
- e.g. ribs of snake and the ribs of a fish (both have similar evolutionary origin)
What is Chordata
The phylum for animals with backbones
What is mammalia
The class for mammals
- features such as: hairy skins and produces milk to feed young
What is a hierarchy
smaller groups are placed within larger groups, WITH NO OVERLAP BETWEEN GROUPS
What is meant by a phylogenetic group
Grouped on evolutionary relationship
What is the evidence for phylogenetic classification
- DNA, mRNA, or amino acid sequences
- DNA hybridisation
- Immunology
- Behaviour
How do scientists use DNA hybridisation for phylogenetic evidence
1) DNA for a specific gene is extracted from 2 different species and mixed
2) DNA split apart by heat (breaks hydrogen bonds between complementary base pairs)
3) single-stranded DNA bonds randomly between species when cooled
4) Radioactive labels that only binds to single strands is added
5) DNA slowly heated and radioactivity is measured
6) the fewer base pairs have formed between strands, the lower the temp they split apart and the sooner radioactivity is detected
7) the more base pairs formed = the more recent the ancestor = the closer related the species are
How do scientists use embryonic evidence for phylogenetic evidence
- similarities in embryos give us guidance in the classification: the more similar embryos look the closer they are phylogenetically
- this is also evidence that organisms have evolved from a common ancestor
How do scientists use behavioural evidences for phylogenetic evidence
- similar behaviours suggest a similar evolutionary origin
- e.g. both humans and chimpanzees live in social groups and have similar facial expressions
How do scientists use immunological evidence for phylogenetic evidence
Using the example of a rabbit
1) inject human serum into rabbits
2) rabbit provides antibodies specific to the human serum proteins
3) sensitised rabbit serum (containing antibodies) is removed from rabbits
4) this serum is then added to the test tubes that contain the blood serums of other species
5) The higher the precipitate formed, the closer the evolutionary relationship
