Evolution: Anatomical and Molecular Homologies

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Questions and Answers

Which of the following best explains why the forelimbs of mammals like humans, cats, whales, and bats, despite having different functions, share the same arrangement of bones?

The environment dictates the bone structure of organisms, leading to similar structures in different species.
Natural selection always leads to the same structural solutions in different species.
These mammals share a common ancestor from which they inherited the basic bone structure, which was then modified over time through evolution. (correct)
They all evolved independently to have the most efficient bone structure for their respective functions.

What is the significance of pharyngeal arches in vertebrate embryos?

They are only present in fish embryos and develop into gills.
They determine the species of the vertebrate.
They are anatomical homologies that develop into different structures with different functions in adult organisms. (correct)
They are vestigial structures with no function in the embryo.

Vestigial structures, such as the remnants of leg bones in snakes, provide evidence for which of the following?

Snakes are devolving.
Snakes evolved from organisms with similar structures. (correct)
Snakes spontaneously generate these structures.
Snakes are developing new structures.

If a gene is found in both humans and bacteria, and it performs the same function in both, what does this suggest about the gene?

The gene was likely inherited from a distant common ancestor. (C) Signup and view all the answers

What is the significance of the genetic code being nearly universal among all living organisms?

It indicates that all species descended from a common ancestor that used this genetic code. (A) Signup and view all the answers

What does the presence of inactive 'pseudogenes' in an organism's genome suggest?

The ancestral species had an active gene. (D) Signup and view all the answers

How do homologous characteristics support the concept of 'descent with modification'?

They demonstrate how traits in different species originate from a common ancestor and diverge over time through natural selection. (B) Signup and view all the answers

Tetrapods are a group of vertebrates that include amphibians, mammals, and reptiles. Which characteristic is shared by all tetrapods but not by other vertebrates?

Limbs with digits (A) Signup and view all the answers

What best describes the pattern formed by homologous characteristics?

A nested pattern where all life shares the deepest layer and each successive smaller group adds its own homologies. (A) Signup and view all the answers

How do evolutionary trees represent the relationships among groups of organisms?

Evolutionary trees represent evolutionary relationships among groups of organisms. (A) Signup and view all the answers

Flashcards

Homology Definition

Similarity resulting from common ancestry.

Homologous Structures

Structures in different species that have a similar underlying anatomy due to common ancestry, but may have different functions.

Vestigial Structures

Remnants of features that served a function in the organism's ancestors, but may have marginal or no importance in the current organism.

Evolutionary Tree

Diagram reflecting evolutionary relationships among groups of organisms based on common ancestry.

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Tetrapods

Characterized by a backbone and limbs with digits.

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Study Notes

Evolution evidence comes from similarities analysis among different organisms.
Evolution involves descent with modification through natural selection.
Ancestral organism traits change in descendants due to environmental conditions.
Related species share similar characteristics with underlying similarity but different functions.
Homology involves similarity from common ancestry used for predictions and explanations.

Anatomical and Molecular Homologies

Evolution remodelling predicts closely related species share similar features.
These shared features relate species and give evolutionary context.
Mammal forelimbs (humans, cats, whales, bats) show the same bone arrangement.
Forelimbs have different functions like lifting, walking, swimming, flying.
Striking resemblances are unlikely if structures arose independently in each species.
Homologous structures underlie skeletons of mammalian limbs, which vary from a structural theme that was present in their common ancestor.

Mammalian Forelimbs

Comparing early development reveals anatomical homologies unseen in adults.
Vertebrate embryos have tails posterior to the anus and pharyngeal throat arches.
Homologous throat arches develop into different structures like gills, ears, and throats.

Anatomical Similarities in Vertebrate Embryos

"Leftover" structures of marginal significance may be present in organisms.
Vestigial structures are remnants of functional features in ancestors.
Snake skeletons have pelvis and leg bone vestiges of walking ancestors.
Blind cave fishes have buried eye remnants under scales.
Vestigial structures indicate snakes and blind cave fishes share common origins.
All life uses the same genetic code, implying descent from common ancestors.
Molecular homologies extend beyond a shared code.
Humans and bacteria share genes from a distant common ancestor.
Homologous genes gain new functions or retain original functions like ribosomal subunits.
Organisms can have non-functional genes; homologous genes may be functional in related species.
Inactive "pseudogenes" are present because a common ancestor had them.

Homologies and Tree Thinking

Homologous features, like the genetic code, are shared by all species due to deep ancestry.
Recently evolved homologous features are shared within smaller organism groups.
Tetrapods (amphibians, mammals, reptiles) have limbs with digits.
Vertebrates have a backbone.
Homologous features form a nested pattern.
All life shares the deepest layer (vertebrate backbone).
Each smaller group adds homologies (tetrapod backbone and limbs with digits).
The nested pattern comes from descent with modification from a common ancestor.
Evolutionary tree diagrams represent descent patterns from common ancestors and show evolutionary relationships.

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Description

Explore the concept of evolution through anatomical and molecular homologies. Discover how shared features among species reveal evolutionary relationships and adaptations. Learn about homologous structures, like mammal forelimbs, and their underlying similarity despite different functions, highlighting common ancestry and evolutionary modifications.