5. Variation, Evolution, Classification

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• _Allele

• _Gene

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Terminology

• _Allele

• _Gene

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Variation

• _{Explain how some phenotypes are affected by alleles}

at many loci (polygenic inheritance) as well as the environment (e.g. height) and how this can give rise to phenotypes which show continuous variation.

• _{Explain how a phenotype of an organism is the result}

of an interaction between genotype and the

environment (e.g. animal hair colour, human height, MAOA and cancers), but the data on the relative

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Types of Variation

Discontinuous

• _{Characteristic has a few}

discrete categories – represented by a bar chart

• _{Variation is usually}

controlled by a single gene.

Continuous

• Characteristic has a continuous range and does not fall into discrete categories –

represented by a line graph.

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% of

population of Britain

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If measurements could be made to the nearest millimetre there would be a smooth transition in the heights

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Phenotypic Variation

• _{Phenotype = genotype + environment.}

• _{For identical twins, because their genotype is}

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Mean, Median, Mode

• _{Mean – add them all up and divide by number}

there.

• _{Median – the middle value}

• _{Mode – the most frequent number}

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Phenotype Type of Twins

Identical Non-identical

Mean height

difference 1.7 4.4

Mean mass

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Mean height

difference 1.7 4.4

Mean mass

difference 1.9 4.6

• _{The 1.7 mean height difference for the identical twins must}

be due to the environment since their have identical

genetics. Since 4.4 – 1.7 = 2.7 – for the non-identical twins 2.7 difference must be due to their different genetics. So in this case genetics has a greater influence on height than the environment.

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Mean IQ

difference 5 8

• _{The 5 mean IQ difference for the identical twins must be due}

to the environment since their have identical genetics. Since 8 – 5 = 3 for the non-identical twins 3 IQ point difference

must be due to their different genetics. So in this case

genetics has a smaller influence on IQ than the environment.

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Examples of the interaction of genes and

the environment

• _{Animal hair colour} • _{Human height}

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Species

• _{A species is a group of individuals that are able}

to interbreed to produce fertile offspring.

• _{When it is not possible to study whether they}

produce fertile offspring, their behaviour, anatomy and physiology can be studied.

• _{You can also study how similar their DNA is to}

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Adaptations of organisms can be classified

into three groups:

• _{Physiological}_{– the chemical reactions going}

on inside the cells of organisms

• _Anatomy_{– what their body looks like e.g.}

longer legs/ wings

• _Behavioral_{– how the organisms behaviors e.g.}

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Evolution by Natural Selection

• _{There is genetic variation is the population as new alleles arise} by mutation.

• _{A change in the environment leads to a selection pressure –} some individuals are better adapted than others.

• _{Those organisms that are best adapted are able to survive and} breed and pass on their advantageous alleles to their offspring. • _{Over several generations these advantageous alleles become}

more frequent in the population.

• _{Competition, predation and disease can produce selection}

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• _{Allele frequency}_{- is the proportion of an}

allele out of the total alleles for one gene.

• _{E.g. Gene for tongue rolling R, r}

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How genetic variation is produced

• _{Produced by meiosis}

• _{Crossing over – exchanging genetic material}

between the end of the chromatids in prophase 1

• _{Independent Assortment – the order the}

chromosomes orientate themselves on the spindle in metaphase 1.

• _{Random fertilization of gametes}

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Example

– Peppered Moth

• _{The peppered moth exists in two forms – a}

mottled (black and white) form and a melanic (black) form

• _{When the air is free of pollution the barks of}

trees are mottled and so the mottled form of the peppered moth is well camouflaged.

• _{It is therefore able to survive and breed and}

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• _{If the environment changes and the air becomes}

polluted the bark of trees becomes dark in colour. This means the melanic form of the peppered moth is better adapted because it is better camouflaged

• _{The melanic moths are able to survive and breed so}

over generations the melanic allele becomes more frequent in the population.

• _{The increase in the melanic alleles in the population}

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Classification

• _{We need to classify organisms in order to}

identify and study them

• _{To calculate species richness}

• _{The classification of organisms into specific}

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Taxonomy

• _{Organisms that share specific characteristics}

are placed in the same group

• _{For example, those that have similar}

behavioral, anatomical or physiological

characteristics are in the same group, or those with similar molecular phylogeny (base or

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There are Five kingdoms

• _Animals_{– multicellular; no cell walls, organelles, glycogen}

energy store

• _Plants_{- multicellular, cellulose cell walls, large vacuole,}

chloroplasts, starch grains.

• _Fungi_{– chitin cell walls, multinucleate and some unicellular,}

organelles present; no chloroplasts; glycogen energy store

• _Protoctists_{– single celled eukaryotic organisms}

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There are seven levels of groups in classification:

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• _{As you move down the hierarchy there are}

more groups but fewer organisms in each group.

• _{There more similar different species are to}

each other, the more groups they share.

• _{Species within the same genus are very similar}

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Molecular Phylogeny

• _{Molecular phylogeny is the evolutionary}

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3 Domains System

• _{Proposed by Carl Woese that there are 3 groups} known as the domains: Bacteria, Archaea and Eukarya.

• _{The Prokaryotes are split into two groups – the}

Bacteria and Archaea

• _{Carl Woese built the molecular phylogeny of the} organisms in the 3 domains using ribosomal RNA (RNA present in ribosomes).

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Why is work reviewed by other scientists before

it is published in a journal

• _{Peer review}

• _{To see if the conclusions drawn from data are}

valid (logical)

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Why do scientists critically evaluate data after

it’s been published in a journal?

• _{To check the methods}

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Where can scientists publish

1. Scientific conference/ poster / presentation or lecture

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How did other scientists critically evaluate

Carl Woese’s work?

• _{Woeses’s results were published in a journal} • _{Before publication his work would have been}

peer reviewed by other scientists

• _{His ideas were presented at a conference}

• _{When his paper was published other scientists}

can peer review his work

• _{Other scientists can repeat his experiments to}

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Where do scientists publish their work?

• _Journal

• _{Scientific magazine} • _Internet