Page 51 - CB1.3 Genetic Varation sciPAD

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CB 1.3 GENETIC VARIATION
GENETICS OF POPULATIONS
Overproduction
Populations produce more
offspring than can survive until
maturity. This leads to competition.
Selection
Selection pressures acting on
variation results in some individuals
surviving better than others.
Adaptation
The traits of the fittest individuals
(those that survive and reproduce)
become more common.
Variation
Individuals within the population
vary in many heritable traits, such
as variation in colour.
Natural Selection
Biologists use the word ‘fitness’ to describe how good a particular genotype is at surviving to
reproductive age, finding a mate and producing offspring. Fitness involves an individual’s ability
to survive ‘selection pressures’ (environmental factors which may reduce reproductive success,
e.g. predators, disease, food scarcity, drought, etc.).
Natural selection occurs when populations of organisms are subjected to selection pressures. The
fittest organisms are more likely to survive and pass their genes on to their offspring, producing a
population that is better adapted to the selection pressures of that particular environment. The
genes of less fit individuals are less likely to be passed on to the next generation.
1. Define the term ‘fitness’ from a biologist's point of view. 


2. Describe why there must be variation within a population in order for natural selection to
occur. 


3. Name two sources of genetic variation.
(a) 
(b) 
4. Summarise the process of natural selection by putting the following statements in the
correct order. The first one has been done for you.
Order of statement Statement
Individuals in a population show variation.
Survivors pass on their alleles to the next generation.
Individuals with less favourable characteristics within the
population are killed due to selection pressures.
Individuals that are better adapted will survive, breed
and produce offspring.
Over time, successful alleles become more common and
unsuccessful alleles are removed.
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