7.3 EVOLUTION MAY LEAD TO SPECIATION

SPECIES:

Similar morphological and physiological features.

That can breed together to produce fertile offspring.

WHAT DOES SELECTION CHANGE?

It changes gene pools, causing a species to change greatly over time..

SPECIATION:

When an existing species gives rise to two or more new species.

The process whereby one gene pool gives rise to more than one gene pool.

WHY MAY INDIVIDUALS IN A POPULATION OF A SPECIES SHOW A WIDE RANGE OF VARIATION IN PHENOTYPE?

ALLOPATRIC SPECIATION:

1. Geographical separation.

2. Reproductive isolation, separating gene pools.

3. Preventing gene flow.

4. Random mutations cause genetic variation in each population.

5. Different selection pressures.

6. So different advantageous alleles passed on in each population.

7. Allele frequencies in each population change over many generations.

8. Eventually, two new species formed that cannot interbreed to produce fertile offspring.

SYMPATRIC SPECIATION:

1. Mutations lead to reproductive isolation, separating gene pools.

2. Preventing gene flow.

3. Different selection pressures.

4. So different advantageous alleles passed on in each population.

5. Allele frequencies in each population change over many generations.

6. Eventually, two new species formed that cannot interbreed to produce fertile offspring.

HOW CAN REPRODUCTIVE ISOLATION OCCUR?

1. Seasonal/Temporal: Two populations reproduce at different times of the year.

2. Mechanical: Anatomical differences may prevent mating from occurring.

3. Behavioural: Two populations have different courtship patterns.

4. Gamete Incompatibility.

GENETIC DRIFT:

• Evolution can also occur by genetic drift.

• Bigger effect on smaller populations because the gene pool is small.

• Genetic Drift is when allele frequencies in a population change over generations due to chance.

• This can reduce genetic diversity; some alleles can become fixed and others lost.