A.S Biology Unit 2.15.1 Evidence for relationships between organisms

aimee1234's version from 2015-04-11 08:12


Question Answer
How can DNA be compared directly using DNA sequencing?The DNA of organisms can be directly compared by looking at the order of bases (As, Ts, Gs and Cs) in each. Closely related species will have a higher percentage of similarity in their DNA base order, e.g. humans and chimps share arounf 94%, humans and mice share around 85%. DNA sequence comparison has led to new classification systems for plants, e.g. the classification system for flowering plants is based almost entirely on similarities between DNA sequences.
How is DNA hybridisation used to see how similar DNA is without sequencing it?1.DNA from two different species is collected, separated into single strands and mixed together. 2.Where the base sequences of the DNA are the same on both strands, hydrogen bonds form between the base pairs by specific base pairing. The more DNA bases that hybridise (bond) together, the more alike the DNA is. 3.The DNA is then heated to separate the strands again. Similar DNA will have more hydrogen bonds holding the two strands together so a higher temperature (i.e.more energy) will be needed to separate the strands.
What is the other way (asides from DNA) that species can be compared?By looking at their proteins (which are coded for by their DNA). Similar organisms will have similar proteins in their cells.
Name the two ways in which proteins can be compared.1.Comparing amino acid sequence 2.Immunological comparisons
How can proteins be compared by comparing amino acid sequences?Proteins are made of amino acids. The sequence of amino acids in a protein is coded for by the base sequence in DNA. Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins.
How can proteins be compared by immunological comparisons?Similar proteins will bind the same antibodies. E.g. if antibodies to a human version of a protein are added to isolated samples from some other species, any protein that's like the human version will also be recognised (bound) by that antibody.
Why is courtship behaviour carried out by organisms?Courtship behaviour is carried out by organisms to attract a mate of the right species.
What can courtship behaviour include?It can be fairly simple - e.g. releasing chemicals, or quite complex, e.g. a series of displays.
What is courtship behaviour and so what does this prevent and so why is this useful?Courtship behaviour is species specific - only members of the same species will do and respond to that courtship behaviour. This prevents interbreeding and so makes reproduction more successful (as mating with the wrong species won't produce fertile offspring)
Why can courtship behaviour be used to classify organisms?Because it is species specific. The more closely related species are, the more similar their courtship behaviour.
Examples of courtship behaviour?1.Fireflies give off pulses of light. The pattern of flashes is specific to each species. 2.Crickets make sounds that are similar to Morse code, the code being different for different species. 3.Male peacocks show off their colourful tails. The tail pattern is only found in peacocks. 4.Male butterflies use chemicals to attract females. Only those of the correct species respond.

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