Exam 3: 9

Question 1

Homoplasy

Answer 1

A trait shared among two or more species that is NOT the result of shared ancestry

Question 2

What are some possible reasons for homoplasy?

Answer 2

• Shared environmental conditions

Question 3

Type of homoplasy: Reversal

Answer 3

• When a trait that was once gained, it lost
• When two organisms share a trait, but in one organism the trait is derived (apomorphy), and in the other organism the trait is ancestral (pleiomorphy)

Question 4

Type of homoplasy: Convergence/parallelism

Answer 4

• When a trait is gained more than once on a phylogeny
• When two organisms share a trait, but it is not due to shared ancestry

Question 5

Why is the opposite of homoplasy consistency?

Answer 5

• If a trait is homoplasious, it evolved more than once
• If a trait is perfectly consistent, it evolved only once.

Question 6

3 types of homology

Answer 6

• Orthology
• Paralogy
• Xenology

Question 7

Orthology

Answer 7

A feature found in multiple lineages that is derived the splitting of species

Question 8

Paralogy

Answer 8

Features found in one or more lineages that are derived from a duplication within a single organism

Question 9

Xenology

Answer 9

Features found in one or more lineages that are derived from horizontal transfer between lineages

Question 10

How do we determine homology?

Answer 10

• If the structures have the same function, they may be homologous (but may be different too)
• Same form? (Usually vary in form)
• Same context? (Less likely to be in error than the two mentioned above)
• Developmental origin?? (Same problems but less likely to be in error because it takes into account less superficial information)
• Ancestry and historical origin??? (Direct matches up with out definition of homology, but we might never know the “true” phylogeny based on it — almost always hypothetical and cannot be proven)