Ori

gin

of

Life

PANSPERMIA

A comet or meteorite brought micro-organisms

TIDAL POOLS

UV light / electrical discharges through volcanic gases onto water

UNDERSEA THERMAL VENTS

Gases, energy and catalysts (metal sulphides)

Theories of Origins of LifeEVIDENCE (can’t do experiments!)Fossils, biochemical links, DNA testing

3 MAIN THEORIES:Panspermia, Thermal vents, Tidal pools, lightning & volcanoes

REQUIREMENTS:water, energy (heat / lightning), inorganic mol.s or gases

Panspermia theorists don’t believe the correct conditions were available at the time that life arose on Earth

All agree that basic nucleotides, were vital in order to reproduce organic molecules

Scientists have been able to manufacture organic molecules in the laboratory in the presence of water, heat and gases.

Chloroplasts and mitochondria both have nucleic material.

They may have been separate organisms which were incorporated into cells

Genetic variation

MEIOTIC MUTATIONS source of all variation – gamete genes are different

SEXUAL REPRODUCTION increases variation – different combinations of genes in gametes

1. cross-over and recombination

2. independent assortment of chromosomes

3. fertilisation - fusion of random gametes

Gene Pools

Species may be divided into populations or demes by geographical obstacles

Population - group of individuals of the same species which can interbreed

Gene pool is the total group of genes available for reproduction in a population

Gene flow – movement of genes from one population to another via gametes

Deme – local unit of a population

Genetic equilibrium – allele frequencies of a population remain unchanged from

generation to generation (Hardy-Weinberg)

Geographical barriers isolate gene pools and prevent normal gene flow

between demesmountains

glaciers

sea

riversPOPULATION

1POPULATION

2

Hardy-Weinberg Theorem

Allele frequencies in a population remain constant - from generation to generation unless disturbed.

Hardy–Weinberg equilibrium is impossible in nature

Ideal state baseline to measure genetic change against.

non-random mating, mutations, selection, limited population size, "overlapping generations", random genetic drift, gene flow and meiotic drive.

Gene pool stability

Large population

Random mating

No gene flow

No mutations

No Natural selection

Small population

Assortative mating

Gene flow (migration)

Mutations

Natural selection

Gene pool change

Hardy Weinberg theory true

Not true - microevolution

Videos

• Prof Wolfe: Fossil formation, dating & indexing• Prof Wolfe: Biochemical similarities