Unit 2: Change and Diversity in Life on Earth Learning Goal 3: Explain the factors that can lead to speciation.

Phenotype Observable characteristics (green eyes, brown hair, purple flowers, etc.)

Genotype Genetic makeup of an organism determined by a pair of alleles.

All in the Genes The genetic make-up of an organism is known as its genotype. An organism’s genotype and the environment in which it lives determines its total characteristic traits i.e. its phenotype. Genotype Phenotype commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG

DNA The double-helix structure of DNA was discovered in 1953. This showed how genetic information is transferred from one cell to another almost without error. Watson and Crick and their model of DNA DNA replication www.chem.ucsb.edu/~kalju/chem110L/public/tutorial/images/WatsonCrick.jpg en.wikipedia.org/wiki/DNA

Gene Unit of hereditary information Located on a chromosome Contains DNA Genes are passed from parent to offspring.

Gene Pool Consists of all the genes that are present in a population.

Mutation However, occasional mutations or copying errors Types of mutation However, occasional mutations or copying errors can and do occur when DNA is replicated. Mutations may be caused by radiation, viruses, or carcinogens. Mutations are rare and often have damaging effects. Consequently organisms have special enzymes whose job it is to repair faulty DNA. Mutant fruitfly upload.wikimedia.org/wikipedia/commons/7/79/Types-of-mutation.png humansystemstherapeutics.com/bb.htm

Genetic Variation Mutations Any change in a sequence in DNA. Few mutations lead to increased fitness. Most mutations are harmful. Species with greater genetic variability are more likely to adapt to changing environments.

Variation Nevertheless, some mutations will persist and increase genetic variation within a population. Variants of a particular gene are known as alleles. For example, the one of the genes for hair colour comprises brown/blonde alleles. majorityrights.com/index.php/weblog/comments/racial_variation_in_some_parts_of_the_skull_involved_in_chewing/

Natural Selection population by sexual reproduction. Mutant alleles spread through a population by sexual reproduction. If an allele exerts a harmful effect, it will reduce the ability of the individual to reproduce and the allele will probably be removed from the population. In contrast, mutants with favorable effects are preferentially passed on Selection of dark gene en.wikipedia.org/wiki/Image:Mutation_and_selection_diagram.svg

Natural Selection can affect the distribution of phenotypes in any of three ways: Stabilizing Selection Individuals at the middle of the curve have the greatest fitness. Disruptive Selection Individuals at either end of the curve have greater fitness than those in the middle. Directional Selection Individuals at one end of the curve have a higher fitness than those in the middle or other end.

Speciation Formation of a new species Species: A group of similar organisms that breed together and produce fertile offspring. Gene pools must become separated for them to become different species. http://video.pbs.org/video/1300397304/

Tigon Result of male tiger and female lion mating incaptivity. Offspring are infertile. Separated both geographically and ecologically.

Liger Result of male lion and female tiger mating in captivity. Offspring are infertile.

Speciation

Reproductive Isolation Prevention of mating between formerly interbreeding groups. or The inability of these groups to produce fertile offspring

Fig. 23.6 Four species of leopard frogs: differ in their mating calls. Hybrids are inviable.

Geographic Isolation Physical barrier divides a population These two groups are not able to mate => leads to new species

These squirrels live on opposite sides of the Grand Canyon These squirrels live on opposite sides of the Grand Canyon. This is an example of allopatric speciation.

Temporal Isolation When two or more species reproduce at different times.

SPECIATION IN DARWIN’S FINCHES SPECIAITON IN THE GALAPAGOS FINCHES OCCURRED BY: FOUNDING OF A NEW POPULATION, GEOGRAPHIC ISOLATION which led to … REPRODUCTIVE ISOLATION and CHANGES IN THE NEW POPULATION’S GENE POOL due to COMPETITION.