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Explain Darwin's theory of 'Descent with Modification'.
- Biological populations change over successive generations
- Life evolved from a common ancestor
- History of life is like a tree with branches representing thediversity of life
What is 'Natural selection'
- Gradual, non-random process by which biological traitsbecome more or less common in a population throughdifferential reproductive success = fitness
What are the propositions underlying Darwin's theory of evolution through natural selection?
- More individuals are produced than can survive
- There is therefore a struggle for existence; AKA competition
- Individuals within a species show variation
- Those with advantageous traits will survive and reproduce
- Favourable traits will accumulate over generations
- Changes in environment can lead to new traits being advantageous
What is 'Sexual selection'?
- Animals develop features to help themto maximise their reproductive success
Key to Darwin’s theory of Sexual Selection;
- By making themselves attractive to the opposite sex (intersexual selection,between the sexes
- By intimidating, deterring or defeating same-sex rivals (intrasexual selection,within a given sex)
What is 'Artificial selection'?
- Intentional breeding for certain traits,or combination of traits = Domestication
- Human preferences/selective breeding
- Used by Darwin as analogy to natural selectione.g. fancier pigeons
What are the differences between Archaea and Bacteria?
Archaea;
- Archaea are prokaryotic cells
- Membranes of branched hydrocarbonchains attached to glycerol by ether linkages
-Cell walls contain no peptidoglycan
- Not sensitive to some antibiotics that affectthe Bacteria, but are sensitive to someantibiotics that affect the Eukarya
- Unique ribosomal RNA
Bacteria;
- Bacteria are prokaryotic cells
- Membranes of unbranched fatty acid chainsattached to glycerol by ester linkages
- Cell walls contain peptidoglycan
- Sensitive to traditional antibacterial antibioticsbut are resistant to most antibiotics thataffect Eukarya
What does 'symbiosis' mean?
- Interaction between two different organisms living in close physical association, typically to the advantage of both.
What are the three types of symbiosis?
Mutualism;
- Both the symbiont and host benefit
Commensalism;
- The symbiont benefits with little effect on the host
Parasitism;
- The symbiont benefits to the detriment of the host.
What are Mendel's laws?
Law of dominance;
- In a cross of parents thatare pure for contrasting traits, only one formof the trait will appear in the next generation
Law of segregation;
- During the formation ofgametes (egg, sperm), the two allelesresponsible for a trait separate from each other. Alleles are then recombined at fertilisation,producing the genotype for the trait of theoffspring
Law of independent assortment;
- Alleles for different traits are distributed togametes (and offspring) independently of oneanother
- Mendel bred true breeding plants with yellowround seeds (YYRR, gamete YR) against greenwinkled seeds (yyrr, gamete yr)
- F1 had genotype YyRr and yellow round seedphenotype
- F2 showed phenotypes in ratio of 9:3:3:1consistent with an independent assortmentmodel
What is the 'Chromosome theory of inheritance'.
- The nuclear substance controls the form and functionof every cell, and divides at mitosis to give equalproducts
- Eggs must lose half their nuclear substance in the polarbody before fertilization, and this must be replacedexactly by the nuclear substance of the sperm
- Because sexual reproduction depends on addingtogether the egg and sperm nuclei in every generation,there must be a halving of the nuclear substance in bothmale and female germ cells
- There are no essential differences between thenuclear substance of eggs and sperm
- Sexual reproduction is a means of producing variabilitybetween individuals, on which natural selection can act
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