Evidence for relationships between organisms. (UNIT 2) Flashcards
What changes when organisms evolve and why does this cause a change?
Changes in DNA.
DNA determines the proteins of an organism including enzymes and proteins determine the features of an organism.
When one species gives rise to another species during evolution, the DNA of the new species will initially be…
Very similar to that of the species that gave rise to it.
When new species are created, why does there DNA gradually become more different from the species they arose from?
Due to mutations, the sequence of nucleotide bases in the DNA of the new species will change.
You would expect species who are more closely related to show…
more similarities in their base sequences than species that are more distantly related.
What property of the DNA double helix does DNA hybridisation rely on?
When DNA is heated, its double strand separates into its two complementary single strands.
When cooled, the complementary bases on each strand recombine with each other to reform the original strand.
Describe the process of DNA hybridisation.
- DNA from two species is extracted, purified and cut into short pieces.
- The DNA from one species is labelled by a radioactive or fluorescent marker to it. It is then mixed with unlabelled DNA from the other species.
- The mixture of both sets of DNA is heated to separate their strands.
- The mixture is cooled to allow the strands to combine with other strands that have a complementary sequence of bases.
- Some of the double strands that reform will be made up of one strand from each species. This is called hybridisation and the new strands are called hybrid strands. IDENTIFIED BECAUSE ARE 50% labelled.
- Strands separated out and the temperature is increased IN STAGES.
- AT each temp. stage the degree to which the new strands are still linked together is measured.
- If two species are closely related they will share many complementary nucleotide bases.
- Therefore be MORE HYDROGEN BONDS linking them together in the hybrid strand.
- The greater the number of hydrogen bonds, the stronger the strand will be.
Describe the relationship between the strength of a hybrid strand and the temp. needed to split it into two strands.
The stronger the hybrid strand (more hydrogen bonds=complementary nucleotide bases), the higher the temperature needed to separate it into two separate strands.
Describe the relationship between temperature needed to split a hybrid strand in two and how closely related a species are.
The higher the temp at which the hybrid strand splits (more hydrogen bonds), the more closely related two species are.
The lower the temp at which the hybrid strand splits , the more distantly the species are related.
Until recently, how were plants classified?
Based on the appearance of a plants physical features.
How was a new classification for plants made up?
3 gene sequence found in ALL plants:
-565 species of plant that between them represented all the known families of flowering plants in the world.
- For each plant, the DNA base sequences of all three genes were determined.
- The sequences for each species were compared using computer analysis.
- A phylogenetic tree for the families of flowering plants was devised based upon the DNA sequences of the species used.
PHYLOGENETIC TREE SHOWED HOW SPECIES HAVE EVOLVED INTO NATURAL GROUPS
What is the sequence of amino acids in proteins determined by?
DNA
What does the degree of similarity in the amino acid sequence of the same protein in two species reflect?
How closely related the two species are.
How are amino acid sequences compared?
Either by counting the number of similarities or the number of differences in each sequence.
What is the principle behind immunological comparison?
The fact that antibodies of one species will respond to specific antigens on proteins in the blood serum of another.
How is the process of immunological comparison carried out?
- Serum albumin (protein) from species A is injected into species B.
- Species B produces antibodies specific to all the antigen sites on the albumin from species A.
- Serum is extracted from species B; this serum contains antibodies specific to the antigens on the albumin from species A.
- Serum from species B is mixed with serum from blood of a third species C.
- The antibodies respond to their corresponding antigens on the albumin in the serum of species C.
- The response is the formation of a precipitate.
- The greater the number of similar antigens, the more precipitate is formed and the more closely related the species are.
- The fewer the number of similar antigens, the less precipitate is formed and the more distantly related the species are.