originally, classification systems were based on observable features but more recent approaches draw...
TRANSCRIPT
Originally, classification systems were based on observable features but more recent approaches draw on a wider range of evidence to clarify relationships between organisms.
Page 66 booklet.
• What is a gene?
• DNA codes for all of the proteins in an organism including enzymes
• By comparing the DNA sequences and the proteins they code for we can look for similarities and differences between different organisms.
• When one species gives rise to another, their DNA sequences and hence their proteins will be very similar.
• The more distantly related organisms are the greater the difference in their DNA and proteins.
• Changes in DNA which cause species to evolve are called mutations.
• This is a technique which can be used to compare the DNA base sequence of different species.
• Draw and label a molecule of DNA
DNA hybridisation
• What property of DNA does hybridisation depend on?
• When heated the double strand of DNA separates and when cooled it reforms with complementary base pairing
• Why is the DNA labelled?
• So that hybrid strands can be identified- they will be 50% labelled
• What is the relationship between the number of H bonds shared and the strength of the DNA strand?
• The greater the number of H bonds the stronger the strand.
• Put the title: DNA Hybridisation on your paper then follow the instructions on the next slide carefully.
• Write in the base sequence of the complementary strands of DNA for species X, Y and Z.
• Using a different colour for each species (denoted by a key), colour the DNA of X, Y and Z.
• Now cut the strands apart – make sure you leave the sugar phosphate backbones visible.
• Now try to hybridise the DNA. Choosing complementary strands. Mix X with Y, X with Z and Y with Z.
• Using a felt pen or highlighter indicate the base pairs that are complementary.
• • Which species are the most closely related? How do
you know? •
DNA hybridisation
• What property of DNA does hybridisation depend on?
• When heated the double strand of DNA separates and when cooled it reforms with complementary base pairing
• Why is the DNA labelled?
• So that hybrid strands can be identified- they will be 50% labelled
• What is the relationship between the number of H bonds shared and the strength of the DNA strand?
• The greater the number of H bonds the stronger the strand.
DNA hybridisation in flowering plants
• So how were plants reclassified?
Originally all plants were classified as having one seed leaf (monocotyledons) or 2 seed leaves (dicotyledons).
• All flowering plants have 3 genes in common.
• The DNA base sequence of these genes was determined and compared over many different species.
• Similarities and differences in the DNA base sequences were used to devise a new phylogenetic tree.
A phylogenetic tree for flowering plants
Complete the application question at the top of page 211
• - if you think it would be useful copy figure 4 into your booklet also
• http://www.youtube.com/watch?v=1zOWYj59BXI
• How is the amino acid sequence in a protein determined?
• 3 bases on DNA code for each amino acid. It is the sequence of bases on the DNA which determines the order of amino acids in a protein.
• Thinking about DNA hybridisation – how could similarity between the proteins of different species be used to see how closely related those species are?
• The more similar the sequence of amino acids for a particular protein in two species is, the more closely related they are.
• The amino acid sequence in the alpha and beta chains in haemoglobin were compared.
• Explain what the data suggests about how closely the other 3 species are related to humans? (3)
Species α chain β chainPosition11
Position23
Position87
Position104
Position115
Human Ala Glu Thr Arg Pro
Orangutan Thr Asp Lys Arg Glu
Chimp Ala Glu Thr Arg Pro
Gorilla Ala Asp Thr Lys pro
• Now complete page 67 of your booklet.
Immunological comparison of proteins
• A third way of evidence for relationships between organisms.
Remember module 1?
• What is an antigen and where is it found?
• What is an antibody?
• Read the top of page 68 now.
Immunological comparison of proteins
Rabbit injected with pure human albumin
Human albumin
Rabbit produces antibodies against human albumin
Anti-human antibodies are collected and purified
Dense precipitate produced
Less dense precipitate produced
Chimpanzee albumin
1. Do the Application Exercise on page 211 – 212 of NT text book
2. Answer the summary questions on pg 210.
3. Exam Question 1 page 215 and 2 page 216
Courtship
3.2.9 Originally, classification systems were based on
observable features but more recent
approaches draw on a wider range of evidence to clarify
relationships betweenorganisms.
Organisms can also be classified according to specific behaviours
• Courtship behaviour is a necessary precursor to successful mating.
• Courtship is important in species recognition.
Why is courtship necessary?
• To recognises members of their own species.
• To identify a mate that is capable of breeding.
• To form a pair bond that will lead to successful mating and raising offspring.
• To synchronise mating ensuring the maximum probability that a sperm and egg will meet.
Courtship signals
• Vocal
• http://www.youtube.com/watch?v=9bzotS1ow0Q
• Chemical
http://www.youtube.com/watch?v=GpLRXWZeyBQ
• Visual
• http://www.youtube.com/watch?v=gqsMTZQ-pmE
http://www.youtube.com/watch?v=z922by9_6Fw
The blue footed booby dance
Or a mixture!
• http://www.youtube.com/watch?v=VjE0Kdfos4Y
• Now try the application on page 214 of your text book.
• Then Q 3 and 2 page 216