Adaptation 11

Question 1

What is hybridisation?

Answer 1

• Crossing between two different genotypes (genetic definition)
• Crossing between two different taxa (taxonomic
  definition)
• Rare in vertebrate animals but
  quite common in vascular
  plants

Question 2

Isolating mechanisms that can lead to hybridisation?

Answer 2

- geographical (occurs usually at ecotone)
• ecological
• temporal
• ethological/behavioural
• mechanical
• breeding system
• interspecific incompatibility
• hybrid inviability (post-zygotic)

(usually occur in combinations)

Question 3

Evolutionary consequences of hybridisation?

Answer 3

• little or no effect if hybrid sterile
• merging of gene-pools (if hybrid fertility high)
• hybrid zones, along boundary where two species meet
• introgression: genes from one species incorporated into gene-pool of another

Question 4

How does introgression occur?

Answer 4

• repeated backcrossing of hybrids to one parent

- leads to incorporation of alien genes into genepool with little change of phenotype

Question 5

What is speciation? How does it occur with regards to hybrids?

Answer 5

• the formation of new and distinct species in the course of evolution
• genome repatterning in a hybrid such that fertility is restored and there is reproductive isolation from both
  parents, e.g. in sunflowers
• allopolyploidy

Question 6

Types of polyploidy

- give pathway of allopolyploidy forming fertile young

Answer 6

AAAA - Autotetraploid / Autopolyploid
- genome duplicated

A1A1A2A2 - segmental Allotetraploid
- 2 partially differentiated genomes

AABB - allotetraploid / allopolyploid
- two well differentiated genomes

AA x BB Fertile parents spp.

• > AB Sterile Hybrid
• genome duplication -
• > AABB Fertile allotetraploid