Homologous StructuresIn everyday life, people look like one another for different reasons. Two sisters, for example, might look alike because they both inherited brown eyes and black hair from their father. On the other hand, two people attending an Elvis impersonators’ convention may look alike because they are both wearing rhinestone studded suits and long sideburns. The similarity between the sisters is inherited, but the similarity between the Elvis impersonators is not.

It works the same way in biology. Some traits shared by two living things were inherited from their ancestor, and some similarities evolved in other ways.

HOMOLOGOUS STRUCTURES - traits inherited by two different organisms from a common ancestor that have the same structures, but different functions

EX: mammal forelimbs (ACTIVITY)

Mammal ForelimbsSCAPULA=AHUMERUS=BRADIUS=CULNA=DCARPELS (WRIST)=EMETACARPELS (HAND)=FPHALANGES (FINGERS)=G

Vertebrate Limbs & Common Ancestor

Which limb is not homologous? Why?

B

Bird

B

Whale

Grasshopper

Lizard

Human

A Human

LizardOctopus

Human

LizardLizard

Human

LizardOctopus Lizard

Human

Octopus Lizard

A Human

Octopus Lizard

A Human

Octopus Lizard

Common AncestorsHomologous structures are inherited from common ancestors. The octopus limb could only be homologous to the lizard limb if they both inherited the limb from a common ancestor. This phylogenetic tree shows how the octopus is related to vertebrate limbs. Vertebrate limbs and octopus limbs evolved independently after their point of common ancestry, so they were not inherited from a common ancestor. Therefore, they are not homologous. The same is true of the grasshopper leg.

Can Genes be Homologous?

Homologous OR NotGAME

1. Are all of these different leaves Homologous?

2. Wings of a bat and a robin?

3. Scales on a brown trout and a lizard?

4. Front teeth on a beaver and the tusks on an elephant?

5. Wings of a dragon fly and the wings of a butterfly?

6. The limbs of an eagle and the limbs of a penguin?

7. Fins of a shark and the fins of a dolphin?

8. No limbs on a water snake or an eel?

9. Opposable thumbs of the bush baby and the human?

10. Gliding adaptation of the marsupial sugar glider from Australia and the placental gliding squirrel of the Americas?

Answers1. Yes2. No3. No4. Yes5. Yes6. Yes7. No8. No9. Yes10. No