Evidence for relationships between organisms - Chapter 15 AQA AS Biology
Chapter 15 - AQA AS Biology
- Created by: H.N
- Created on: 01-01-13 19:52
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- Evidence for relationships between organisms
- Genetic comparisons using DNA + Proteins
- Use of DNA base sequencing in classifying plants
- used to be based on the appearance of a plant - flowering plants placed into 2 groups
- monocotyledons - single seed leaf, thin, narrow leaves
- Now - based upon the DNA sequence of 3 genes found in all plants
- sequences for each species compared using computer analysis
- Phylogenetic tree for the families of flowering plants was devised
- sequences for each species compared using computer analysis
- used to be based on the appearance of a plant - flowering plants placed into 2 groups
- comparison of amino acid sequences in proteins
- sequence of a.a. determined by DNA - similarity in a.a. sequence of the same protein 2 species will reflect how closely related they are
- 2 sequences compared by either counting the no. of similarities or counting the no. of differences
- Immunological comparison of proteins
- principle: antibodies of 1 species will respond to specific antigens on proteins, in the blood serum of another
- Occurs as follows:
- sequence of a.a. determined by DNA - similarity in a.a. sequence of the same protein 2 species will reflect how closely related they are
- Use of DNA base sequencing in classifying plants
- Courtship behaviour
- why is it necessary?
- organisms need to reproduce in order for a species to survive over time
- females of most species only produce eggs at specific times of the year - so it's important to ensure successful mating + that offspring have the max. chance of surviving
- What it entails
- Form a pair bond
- leads to successful mating + raising of offspring
- Synchronise mating
- ensures it takes place when there is max. probability of the sperm + egg meeting
- Form a pair bond
- males use courtship behaviour to determine whether females are at the receptive stage
- if female responds with appropriate behavioural response courtship continues + results in production of offspring
- If female exhibits different pattern of behaviour, male ceases to court her
- animals use signals to communicate with a potential mate + members of their own sex
- males usually carry out an action which acts as a stimulus to the female - who responds with her own action
- continues in a STIMULUS- RESPONSE chain
- Same for members of the same species, different for members of different species
- The longer the courtship sequence continues, the more likely mating will occur
- If at any point, 1 of the pair fails to respond appropriately, the courtship sequence ends
- continues in a STIMULUS- RESPONSE chain
- males usually carry out an action which acts as a stimulus to the female - who responds with her own action
- why is it necessary?
- Genetic comparisons using DNA + Proteins
- Comparison of DNA base sequences
- Genetic comparisons using DNA + Proteins
- Use of DNA base sequencing in classifying plants
- used to be based on the appearance of a plant - flowering plants placed into 2 groups
- monocotyledons - single seed leaf, thin, narrow leaves
- Now - based upon the DNA sequence of 3 genes found in all plants
- sequences for each species compared using computer analysis
- Phylogenetic tree for the families of flowering plants was devised
- sequences for each species compared using computer analysis
- used to be based on the appearance of a plant - flowering plants placed into 2 groups
- comparison of amino acid sequences in proteins
- sequence of a.a. determined by DNA - similarity in a.a. sequence of the same protein 2 species will reflect how closely related they are
- 2 sequences compared by either counting the no. of similarities or counting the no. of differences
- Immunological comparison of proteins
- principle: antibodies of 1 species will respond to specific antigens on proteins, in the blood serum of another
- Occurs as follows:
- sequence of a.a. determined by DNA - similarity in a.a. sequence of the same protein 2 species will reflect how closely related they are
- Use of DNA base sequencing in classifying plants
- DNA Hybridisation
- depends upon a property of the DNA double helix
- DNA heated - double strand seperates
- When cooled - complementary bases on each strand recombine to reform orignial strand
- Occurs as follows:
- 1) DNA from 2 species is extracted, purified + cut into short pieces
- 2) DNA from 1 species labelled by attaching a radioactive/fluorescent marker. Then mixed with unlabelled DNA of other species
- 3) mixture of both sets of DNA is heated to separate their strands
- 4) mixture cooled + allowed to recombine
- 5) some of the double strands that reform will be made up of 1 strand from each species = HYBRIDISATION (new strands = hybrid strands)
- Identified because 50% labelled
- 6) hybrid strands separated out + temp. increased in stages
- 7) if species are closely related they will share many complementary nucleotide bases. Therefore more H bonds linking them
- The greater the no, of H bonds, the stronger the hybrid strand + the higher the temp. needed to separate into 2 single strands
- 8) Higher the temp. which the hybrid strand splits, the more closely related, so the lower the temp. the more distantly the species are related
- 7) if species are closely related they will share many complementary nucleotide bases. Therefore more H bonds linking them
- 5) some of the double strands that reform will be made up of 1 strand from each species = HYBRIDISATION (new strands = hybrid strands)
- 4) mixture cooled + allowed to recombine
- 3) mixture of both sets of DNA is heated to separate their strands
- 2) DNA from 1 species labelled by attaching a radioactive/fluorescent marker. Then mixed with unlabelled DNA of other species
- 1) DNA from 2 species is extracted, purified + cut into short pieces
- Genetic comparisons using DNA + Proteins
- When cooled - complementary bases on each strand recombine to reform orignial strand
- dicotyledons - 2 seed leaves, broad leaves
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