Species and Speciation

Question 1

Barriers

Answer 1

For a species to remain distinct, they must remain reproductively isolated –> there are two types of barriers that prevent organisms from interbreeding: pre-zygotic and post-zygotic barriers

Question 2

Pre-Zygotic (Pre-Fertilization) Barriers

Answer 2

• Behavioural: signals to attract mates are unique to a species
• Temporal: mating times (seasons) are different
• Mechanical: physically unable to (ex. incompatible sex organs)
• Gametic Isolation: even if there’s no mechanical isolation and gametes from 2 species fuse, they often fail to produce a zygote (ex. molecules on egg adhere to complementary molecules on sperm of same species)

Question 3

Post-Zygotic (Post-Fertilization) Barriers

Answer 3

• Hybrid Inviability: zygote dies before birth due to genetic incompatibility
• Hybrid Sterility: offspring survives but is sterile (ex. Horse + Donkey = Mule/Hinney)
• Or… hybrid is fertile (F1) but offspring (F2) are weak (ex. cotton either dies as seeds in F1 or is a weak defective plant)

Question 4

Speciation

Answer 4

The formation of a new species –> species both change/evolve and branch into new species

Question 5

Types of Speciation

Answer 5

Sympatric Speciation and Allopatric Speciation

Question 6

Sympatric Speciation

Answer 6

Populations become reproductively isolated even when living in same geographic area –> happens when chromosomes suddenly change

Question 7

Allopatric Speciation

Answer 7

Population split into 2 isolated groups due to a geographical barrier –> gene pools become so different they can no longer successfully interbreed, even if brought back together