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Determining relatedness between species using molecules - Differences in DNA If two populations become isolated from each other, they will accumulate different mutations in their DNA. As time passes, the sequence of nucleotides in their DNA becomes more different and what was once similar DNA gradually diverges
Determining relatedness between species using molecules - Differences in amino acid sequences As two species diverge, they accumulate different mutations in their DNA and start accumulating differences in the amino acid sequences of their proteins. The more time that has passed, the more differences there are between their amino acid sequences
Molecular clocks Technique that uses the rate of accumulation of mutations in DNA to calculate how long ago organisms diverged from one another Changes in DNA and proteins are constant over evolutionary time and across different lineages
Molecular clock hypothesis The molecular clock hypothesis can be applied by calculating the rate of mutation of a region of DNA, along with the number of differences between the DNA of two organisms, and using this information to estimate how long ago they diverged
Molecular clock limitations Assumption that the rate of genetic change is constant and therefore accurately represents evolutionary time In order to genetic changes to occur at a constant rate, those changes or mutations need to be neutral or not affected by natural selection
Mitochondrial DNA as a molecular clock Mutations in mtDNA accumulate over time mtDNA does not have the same repair mechanisms as nuclear DNA rate of mutation in mtDNA is usually higher than in nuclear DNA Used as a molecular clock in relatively closely related species
DNA hybridization technique technique that can be used to determine the level of similarity between sections of DNA of two species
DNA hybridisation step 1 1. Both species double-stranded DNA is heated to 95°C to break the hydrogen bonds between complimentary bases and separate the individual strands DNA.
DNA hybridisation step 2 2. The individual strands of DNA of the two species are mixed together and allowed to cool. Where the nucleotide bases of the two species genes are complimentary, hydrogen bonds will form, creating a strand of hybridised DNA.
DNA hybridisation step 3 3. The level of similarity is measured by reheating the hybrid DNA molecule. The temperature needed to separate half of these molecules is recorded as the melting temperature or thermal stability.
DNA hybridisation step 4 4. The higher the temperature the more related the species
DNA sequencing provides a more accurate measure of sequenced differentiation by allowing a direct comparison of the nucleotide sequences DNA sequencing is the determination of the base (nucleotide) sequence of a gene.
Phylogenetic trees (evolutionary trees) Branching diagrams that show inferred evolutionary relationships or lines of evolutionary descent among biological groups from molecular data Molecular evidence includes amino acid sequences of proteins, RNA sequences, and DNA sequences
Master regulatory genes Control the expression of other regulatory and structural genes during embryonic development They are essential for the correct embryonic development of organisms Master regulatory genes are able to switch other genes ‘on’ or off
Cichlid fish - where they are Lake Victoria is home to about 500 cichlid species, Lake Malawi is home to about 800 to 1000 other cichlid species, and Lake Tanganyika is home to about a further 250 different species of cichlid
Cichlid fish - feeding habits The different cichlid species in each lake show great diversity in structure and behaviour, in particular in their feeding habits Some graze on algae growing on rocks, some feed on algae growing on other algae, some prey on fish and dine on flesh
Cichlid fish - habitats cichlid species occupy different habitats in the lakes, including rocky areas, sandy shallows and deep water
Cichlid fish - regulatory genes Existence of a master regulatory gene that controlled the rate of gene expression of genes involved in the development of length, width and depth of the cichlid’s jaw
Cichlid fish - BMP4 at higher levels When BMP4 is expressed at higher levels, as occurs in the biting cichlids, the jaw develops into a shorter, robust structure, with teeth that are small and closely spaced
Cichlid fish - BMP4 at lower levels when BMP4 expression is reduced, as occurs in cichlids that feed by suction, the jaw is more elongate and the teeth are larger and spaced like a comb
Galapagos finches The specialised beak shapes of the Geospiza finches are also determined by differential patterns of expression of the BMP4 gene
Galapagos finches - BMP4 at lower levels low expression of BMP4 was detected in the mesenchyme (embryonic tissue that can develop into bone and cartilage) of the upper beak and this correlated with low beak width and depth
Galapagos finches at higher levels high expression of BMP4 is correlated with beaks of greater widths and depths
CaM gene encodes the signalling molecule, calmodulin, has been found to control beak elongation. Calmodulin is a calcium-binding protein that regulates the action of other cell proteins involved in development.
summary part 1 Master genes, such as BMP4 and CaM, control aspects of embryonic development. Slight variations in the timing, levels, and sites of expression of the BMP4 gene can generate a range of novel jaw phenotypes in cichlids and beak phenotypes in finches
summary part 2 Expression of BMP4, a master gene, during embryonic development of cichlid fish controls jaw shape in the developing cichlid fish embryos, and beak shape in finches. The product of the BMP4 gene is a signaling molecule, bone morphogenetic protein 4.
summary part 3 Higher levels of BMP4 expression in the cichlid embryo result in a shorter and more robust jaw, and wider and deeper upper beaks in finch embryos.
summary part 4 The BMP4 gene controls beak width and depth and its expression results in the development of the broader, heavier beaks found in the seed-eating finches.
summary part 5 The CaM gene controls beak length, and its expression produces the longer probing beaks of the cactus finches
Created by: emmawalton05
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