Biology Revision Notes - Population Genetics

AQA Biology, Energy and Continuity - Population Genetics

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Biology Revision Notes - Population Genetics:
Population ­ A group of individuals of the SAME SPECIES in the SAME
PLACE (habitat) at the SAME TIME
Variation ­ differences in PHENOTYPES of organisms within a
population
Effects of inbreeding and out breeding:
o INBREEDING ­ INCREASES the proportion of HOMOZYGOUS
INDIVIDUALS and MAGNIFIES GENETIC DISORDERS resulting in
harmful recessive alleles
o OUTBREEDING ­ INCREASES the proportion of HETEROZYGOUS
INDIVIDUALS and INCREASES GENETIC VARIATION within a
species
Types of genetic variation:
o Discontinuous Variation:
CLEAR ­ CUT differences in with NO INTERMEDIATES e.g.
sex in animals and plants, tongue rolling, Huntington's
chorea
Few Genes
Little Environmental Factors
o Continuous Variation:
Complete GRADATION from one extreme to another with
NO GAPS e.g. tree height, dog mass, hand span
Many genes
Lots of environmental factors
Twin Studies:
o MONOZYGOTIC ­ Identical twins, zygote splits at early stage,
each part develops into a twin
o DIZYGOTIC ­ Non-Identical twins, two ova are fertilised,
develop separately, no more similar than any other siblings

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