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Evolution (Incest and Bestiality)

Aoife McLysaght Genetics

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What is Life?

What is Life?

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What is Life?

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It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for DNA.

Watson & Crick, 1953

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A T

C G

T A

G C

T A

C G

T A

G C

A T

C G

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DNA can make copies of itself

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10 generations … >1000 ancestors

20 generations … > 1 million ancestors

30 generations … > 1 billion ancestors

Looking back …

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Amphioxus Phylum Chordata

(but not a vertebrate)

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Histone 4 •  Two copies in Histone

octamer •  Forms complex with

other histones and binds DNA into chromatin

•  Almost the whole protein is highly constrained

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Histone 4 •  Highly conserved protein

•  Compare human and wheat H4 genes

•  55 DNA differences •  2 amino acid differences

–  Val Ile (both aliphatic) –  Lys Arg (both charged)

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Course aims

•  Look at evidence for evolution •  Discuss how to measure evolution •  Describe evolutionary processes

Fossil record

Transitions

Extinctions

Sinosauropteryx

Dromaeosaurid dinosaur

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Heredity

•  In Darwin’s time the mechanism of heredity was not understood.

•  Popular idea: blending inheritance

Gregor Mendel

•  Monk in Brno in present-day Czech Republic

•  Experimented on inheritance in peas –  easy to cultivate –  easily observable traits –  easy to know which

are the parents of the new generation

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Two Alternative Traits of the Seed Shape Character

Note that each of seed is a new individual of a different generation – seeds are not of the same generation as the plant that bears them.

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Mendel had discovered that heritability is mediated by discrete particles that do not blend.

Mendel had discovered genes

Later work showed that genes are on chromosomes and that the information was stored in DNA

How does evolution happen?

•  Heritable variation in the ability to survive and reproduce in your environment

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Heritable variation •  DNA mutations

Mutations generate new alleles

Allele = variant form of a gene.

… in the ability to survive and reproduce

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… in your environment

•  “Better” or “fitter” is subjective – context dependent

green = malarial region; red stripes = high frequency of sickle-cell anaemia

Key ideas:

1.  Gradual evolution results from small genetic changes that are acted upon by natural selection

2.  The origin of species (macroevolution) can be explained in terms of natural selection acting on individuals (microevolution)

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Genes are the key to evolution

•  Genes are both the material of evolution, and the markers of evolution

•  [material] They are the heritable characters that change and result in evolutionary changes

•  [markers] They are also our major source of information for understanding the process of evolution

•  Mutations occur in DNA sequences giving rise to variation

= source of heritable variation

•  Without mutation there is no evolution