Thescienceteacher.co.uk Continuous variation Directional selection Stabilising selection Disruptive selection Natural Selection.

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thescienceteacher.co.uk Continuous variation Directional selection Stabilising selection Disruptive selection Natural Selection

thescienceteacher.co.uk Thus living things face a constant struggle for existence. The individuals in a population vary in their phenotypes.phenotypes Some of this variation is inheritable; that is, it is a reflection of variations in genotype. genotype Living things produce more offspring than the finite resources available to them can support. To the extent that their adaptations are inheritable, they will be passed on to their offspring. Those variants best adapted to the conditions of their life are most likely to survive and reproduce themselves ("survival of the fittest"). Put these sentences in the correct order

thescienceteacher.co.uk Living things produce more offspring than the finite resources available to them can support. Thus living things face a constant struggle for existence. The individuals in a population vary in their phenotypes. Some of this variation is inheritable; that is, it is a reflection of variations in genotype. Those variants best adapted to the conditions of their life are most likely to survive and reproduce themselves ("survival of the fittest"). To the extent that their adaptations are inheritable, they will be passed on to their offspring.phenotypesgenotype

thescienceteacher.co.uk Requirements for Natural Selection 1. Heritable variation in the population 2.Differential survival and reproduction associated with the possession of that trait.

thescienceteacher.co.uk

Continuous Variation

thescienceteacher.co.uk Directional Selection  favours ONE extreme

thescienceteacher.co.uk Stabilising Selection  favours the norm (the mean)

thescienceteacher.co.uk Disruptive selection  favours BOTH extremes

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Giraffes have long necks!!?? The optimum birth weight of a baby is very close to the mean value. Some individuals of the European swallowtail butterfly (Papillio machaon) are brown and pupate on leaves or stems which are brown, others are green and pupate on green leaves or stems – there are very few intermediates.

thescienceteacher.co.uk For each fact… Q1) Draw a rough distribution to show the frequency of the trait you would expect in the population without any selection pressure. Q2) Draw a rough distribution to show the frequency of the trait in the population today Q3) What type of selection gave rise to this distribution?

thescienceteacher.co.uk Are Humans Exempt from Natural Selection?

thescienceteacher.co.uk Are Humans Exempt from Natural Selection? “of all the human eggs that are fertilized, only one-third of so will ever reproduce themselves. “ Mortality selection Some 30% of pregnancies end by spontaneous abortion of embryos and fetuses. 5% by stillbirths and infant deaths. 3% by childhood deaths. Sexual selection Another 20% will survive to adulthood but never marry. Fecundity selection Of those that do marry, 10% will have no children.