A 4.1.4 - biology study for cladistics

What is the definition of a homologous structure?

• A structure inherited from a common ancestor that shares common underlying features, but may have evolved in diverse ways to become adapted for different functions.

What is divergent evolution?

The process where organisms from a common ancestor accumulate differences over time due to exposure to different selective pressures, eventually forming new species.

How does divergent evolution explain why a whale’s flipper and a bat’s wing have the same basic bone layout?

Both inherited the basic structure from a shared common ancestor, but natural selection modified the lengths and shapes over millions of years to adapt to unique ecological niches (swimming vs. flying).

What are five different types of homologous structures across different levels of biological organization mentioned in the slides?

Anatomical structures, embryological patterns, metabolic reactions, molecular sequences, and vestigial structures.

• Match these specific examples from the slides to their homologous category:

  1. Pentadactyl limb

  2. Embryonic gills in reptiles, birds, and mammals

  3. Glycolysis to derive ATP from glucose

  4. Pax6 eye development gene similarities

  5. Pelvis and leg bone remnants in snakes and whales

1. Anatomical Structure

2. Embryological Pattern

3. Metabolic Reaction

4. Molecular Sequence

5. Vestigial Structure

What is a pentadactyl limb?

A 5-digit limb found in tetrapods (amphibians, reptiles, birds, and mammals) that shares the same general bone layout.

What are the four structural groups of bones that make up the layout of a pentadactyl limb from closest to the body to the tips?

• One bone proximal to the body

• Two bones distal to the body

• A group of little bones

• Digit bones at the tips of the limb

Name the specific forelimb and hindlimb equivalents for each of those four bone groups:

• One bone proximal: Humerus (forelimb) / Femur (hindlimb)

• Two bones distal: Radius & ulna (forelimb) / Tibia & fibula (hindlimb)

• Group of little bones: Wrist/carpals (forelimb) / Ankle/tarsals (hindlimb)

• Digit bones: Metacarpals & phalanges (forelimb) / Metatarsals & phalanges (hindlimb)

According to the slides, how do a whale's limb and a horse's limb structurally match their locomotor functions?

A whale's limb is shortened and flattened into a paddle for swimming, while a modern horse has lost side toes to form a single large hoof specialized for standing and running.

What historical trend does the fossil record of the horse reveal about its pentadactyl limb digits over millions of years?

Horse species progressively lost most of their side toes; the middle toe evolved into a single hoof, while the others became smaller and ultimately functionless remnants.