Biology SL chapter 5.4 (Evolution)

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Define evolution
The cumulative change in the heritable characteristics of a population.
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Evidence for evolution
Fossil record, selective breeding and homologous anatomical structures.
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Consequences of overproduction of offspring
When there is an abundance of resources, populations can achieve a very high growth rate. However, more offspring = more competition for resources which leads to struggle for survival. This increases mortality rate as weak members of population die.
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Variation within species
Discontinuous variation: variation caused by a single gene, which leads to distinct classes. Continuous variation: a type of variation controlled by many genes, which leads to a range of characteristics
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Three sources of variation
gene mutations (a permanent change to the genetic composition of an individual) , gene flow(the movement of genes from one population to another via immigration and emigration)and sexual reproduction(the combination of genetic materials from parents)
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Explain how reproduction promotes variation within species
Independent assortment: location of chromosomes during metaphase one. Crossing over: increases number of gamete variations by creating new genetic combinations. Random fertilisation: the mixture of parents' gametes, creating a new combination
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Explain how natural selection leads to evolution
There is genetic variation within a population (cab be inherited) and there is competition for survival. Environmental selective pressures ensure that organisms with beneficial adaptations are more likely to survive and pass on their genes.
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Card 2

Front

Evidence for evolution

Back

Fossil record, selective breeding and homologous anatomical structures.

Card 3

Front

Consequences of overproduction of offspring

Back

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Card 4

Front

Variation within species

Back

Preview of the front of card 4

Card 5

Front

Three sources of variation

Back

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