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Who came up with the theory of particulate inheritance

Gregor Mendel


Who believed in the theory of blending inheritance



What was the theory of blending inheritance

heritable factors blend to produce an intermediate phenotype


Why does the theory of blending inheritance not work

because if offspring phenotypes must always be intermediates of parents, all individuals would look the same after just a few generations


What are the 3 laws of the particulate theory

Law of segregation
Law of independent assortment
Law dominance


What is law segregation

individuals possess two alleles at each gene – one from each parent


What is law of independent assortment:

genes for separate traits are passed on independently from parents to offspring (NB this is not always true - remember linkage disequilibrium?)


What is law of dominance

recessive alleles will always be masked by dominance alleles


What are Darwins four postulates after the modern synthesis

1. As a result of mutation, gene flow and recombination, individuals within populations are variable for nearly all traits.
2. Individuals pass their alleles on to their offspring intact.
3. More offspring are produced than can survive.
4. The individuals that survive and reproduce are those with the alleles that best adapt them to their environment.


What were the two schools of thought on genetic variation within populations until 1960

Classical and Balanced


What did the classical school think

Genetic polymorphisms are rare and mainly deleterious. At each locus, the best allele should be fixed by natural selection


What did the balanced school think

Large amounts of genetic variation are maintained in populations. At each locus, polymorphisms are maintained by “balancing” natural selection


Was the classical or balanced school right in there thinking

Turned out to be both wrong… but to be fair, they didn’t have any data!)


When is it reasonable to use phenotype as a proxy for genotype

for discrete variation, where a trait follows a simple Mendelian inheritance pattern e.g


When is it not reasonable to use phenotype as a proxy for genotype

When you have continuous traits such as height as continous traits are mostly polygenic (controlled by many genes)


Ways you can visualise genetic (protein) variation

gel electrophoresis
microsatellite genotyping


Why was the classical school wrong

polymorphisms are not rare


Why was the balanced school wrong

no evidence that selection maintains all the variation


Who argued for neutralism in the selection-neutralism debate

Motoo Kimura


Who argued for selection in the selection-neutralism debate

John Maynard-Smith


What is the neutralism stance on the evolution at the molecular level (DNA sequence)`

Most variation at molecular level is selectively neutral, fixed by genetic drift
Most non-neutral mutations eliminated by selection
(does not suggest that morphological, physiological and behavioural features evolve by random genetic drift – such features evolve by NS, its just that this make up only a small part of overall molecular variation


What is the selectionism stance on the evolution at the molecular level (DNA sequence)`

Substantial portion of the genome affected by selection
Selection acts on many genes, and also affects linked sites


Reasons why variation is maintained (briefly)

various mutational mechanisms/
recombination, natural selection, gene flow recombination


What is the observed genotype frequency

the proportion of a population that has a certain genotype


What is allele frequency

proportion of a given allele in the population


How to work out the total amount of alleles in sample

number in a sample x2


What are the assumptions of hardy weinburg equilibrium

a. infinitely large population size
b. no mutation
c. no selection
d. no gene flow
e. random mating


What can we test with Hardy weinburg equilibrium

test whether evolution is occurring and see if one or more assumptions are being violated


What is genetic drfit

– random fluctuations in allele frequencies occur as a result of ‘sampling error’ between generations in finite populations


What can genetic drift lead too

Can lead to the replacement of old alleles by new alleles (and the trait they confer) – non-adaptive evolution