Phylogenetics and Chordate Origins

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Questions and Answers

What is a characteristic of a monophyletic group?

It consists of species that do not share a common ancestor.

It includes a common ancestor and all its descendants. (correct)

It includes a common ancestor but not all descendants.

It contains only a single species with no relatives.

Which term describes a unique trait found in a single taxon?

Symplesiomorphy

Autapomorphy (correct)

Synapomorphy

Clade

What is the primary purpose of outgroup comparison?

To establish evolutionary timelines.

To find the earliest common ancestor of all taxa.

To determine relationships among all taxa in the group.

To identify derived traits unique to the ingroup. (correct)

Which of the following accurately describes synapomorphy?

A shared trait present in an immediate ancestor but not in the earliest ancestor. Signup and view all the answers

Which hypothesis suggests that chordates evolved from echinoderm larvae?

Echinoderm Origin Signup and view all the answers

What is NOT a characteristic shared by all chordates?

Presence of a hard exoskeleton Signup and view all the answers

Which type of grouping includes species without a common ancestor?

Polyphyletic Group Signup and view all the answers

Which organism is a modern example of a sedentary tentacle feeder related to hemichordate origin?

Acorn worm Signup and view all the answers

What is the primary function of the amnion in vertebrate development?

Protects the embryo in a fluid-filled sac Signup and view all the answers

Which structure is responsible for gas exchange in embryos?

Allantois Signup and view all the answers

What characterizes anamniotes compared to amniotes?

They do not develop an amniotic sac. Signup and view all the answers

What is the primary role of the yolk sac in mammals?

Source of food for the developing embryo Signup and view all the answers

Which layer of the epidermis is the deepest and contains germinative cells?

Stratum germinativum/basale Signup and view all the answers

Which of the following statements about the integumentary system is incorrect?

The integument is primarily derived from mesoderm. Signup and view all the answers

Which group of vertebrates exclusively form only the yolk sac during development?

Fish Signup and view all the answers

In which type of mammals does the yolk sac provide a rudimentary connection to the mother’s blood?

Marsupials Signup and view all the answers

What is the main function of melanocytes in the epidermis?

Produce melanin Signup and view all the answers

Which layer of the skin is primarily composed of areolar connective tissue?

Dermis Signup and view all the answers

What is NOT a function of the hypodermis?

Contains hair follicles Signup and view all the answers

Which type of chromatophore is responsible for producing yellow, brown, or black pigments?

Melanophores Signup and view all the answers

What is the primary function of the vegetal pole in bird embryos?

Storage of yolk for nourishment Signup and view all the answers

Which glandular structure in amphibians is responsible for secreting mucus and may trigger a fear response?

Club Cells Signup and view all the answers

What is the role of iridophores in the skin of vertebrates?

To cause iridescence Signup and view all the answers

What structural change occurs during gastrulation?

Reorganization of the blastula into a multilayered gastrula Signup and view all the answers

Which of the following correctly describes the germ layers formed during organogenesis?

Endoderm forms digestive and respiratory systems Signup and view all the answers

Which of the following types of multicellular glands secretes toxic products to repel enemies?

Sacciform Cells Signup and view all the answers

Which component of the skin is responsible for providing physiological support and tensile strength?

Dermis Signup and view all the answers

What is the difference between diploblastic and triploblastic embryos?

Triploblastic embryos have three cell layers, while diploblastic embryos have two Signup and view all the answers

In which type of embryos does the blastopore become the mouth?

Protostomes Signup and view all the answers

What role do extraembryonic membranes serve during embryonic development?

They assist in nutrition, gas exchange, and waste removal Signup and view all the answers

What is the main purpose of neurulation in vertebrate development?

Transformation of the neural plate into the neural tube Signup and view all the answers

Which germ layer is primarily responsible for forming muscles and the skeletal system?

Mesoderm Signup and view all the answers

What is the primary function of the epidermis in amphibians?

To facilitate cutaneous respiration Signup and view all the answers

Which layer of skin in reptiles is mostly characterized by extensive keratinization?

Stratum corneum Signup and view all the answers

What distinguishes the integument of birds from other vertebrates?

Presence of feathers Signup and view all the answers

Which type of skin gland in reptiles is involved in reproductive functions?

Fermoral glands Signup and view all the answers

What is the role of the brood patch in birds?

To keep eggs warm during brooding Signup and view all the answers

Which of the following components is NOT found in the integument of mammals?

Feathers Signup and view all the answers

What factors can influence the process of molting in reptiles?

Temperature and humidity Signup and view all the answers

What type of connective tissue is primarily found in the dermis of reptiles?

Fibrous connective tissue Signup and view all the answers

Study Notes

Phylogenetics

Cladograms depict species relationships through branching patterns.
Phylogenetic Trees illustrate evolutionary relationships, including time scales.
Node: Represents a point of divergence.
Branch: Represents an evolutionary lineage.
Clade: Includes a common ancestor and all its descendants.
Synapomorphy: A trait present in the immediate ancestor but not in the earliest ancestor.
Symplesiomorphy: A trait present in both the immediate and earlier ancestors (ancestral/primitive traits).
Autapomorphy: A unique, derived trait found in a single taxon.
Monophyletic Group: Includes a common ancestor and all its descendants.
Paraphyletic Group: Includes a common ancestor but not all descendants.
Polyphyletic Group: Includes species without a common ancestor.

Origin of Chordates

Chordates include vertebrates, sea squirts, and lancelets.
Share characteristics like notochord, dorsally situated central nervous system, and gill slits during development.
Evolved during the Cambrian period from a deuterostome ancestor (related to echinoderms and hemichordates).

Theories of Chordate Origin

Echinoderm Origin: Proposed by Johannes Muller (1860) suggesting echinoderm larvae gave rise to chordates through neoteny (retention of juvenile features into adulthood).
Hemichordate Origin: Proposed by Romer (1959) suggesting ancestral deuterostomes were sedentary tentacle feeders with ciliated, mucous-laden tentacles to trap plankton.
Urochordate Origin: Proposed by W. Garstang (1928) and later supported by N.J. Berrill (1955) based on unequal-sized blastomeres during development with larger ones at the vegetal pole and smaller ones at the animal pole.

Vertebrate Embryonic Development

Types of Eggs:
- Alecithal: Little to no yolk (e.g., mammals).
- Mesolecithal: Moderate amount of yolk concentrated at the vegetal pole (e.g., amphibians).
- Macrolecithal: Large amount of yolk (e.g., reptiles, birds).
Types of Cleavage:
- Holoblastic: Cleavage furrows divide the entire egg (e.g., mammals).
- Meroblastic: Cleavage furrows do not completely divide the egg (e.g., birds).
Gastrulation: Process of reorganizing the blastula into a multilayered gastrula.
- Forms the three embryonic germ layers (ectoderm, mesoderm, endoderm).
- Forms the embryonic gut (archenteron).
- Defines major body axes.
Blastopore: The first opening formed during gastrulation.
- In protostomes, becomes the mouth.
- In deuterostomes (echinoderms & chordates), becomes the anus.
Neurulation: Folding process transforming the neural plate into the neural tube.
- The embryo at this stage is called the neurula.
Organogenesis: Development of organs from the three germ layers.
- Ectoderm: Forms skin, brain, nervous system, teeth, ENT.
- Mesoderm: Forms muscles, skeletal system, circulatory system, kidney, urogenital ducts.
- Endoderm: Forms gut lining, cavities, and organs of the foregut, midgut, and hindgut.
Mesenchymal Stem Cells: Multipotent stromal cells that can differentiate into various types of cells.
Types of Embryos:
- Diploblastic: Two embryonic cell layers (no mesoderm).
- Triploblastic: Three embryonic cell layers.

Extraembryonic Membranes

Assist in embryonic development, originating from the embryo but not part of it.
Functions in nutrition, gas exchange, and waste removal.
Amnion: Protects the embryo in a sac filled with amniotic fluid.
- Amniotes: Develop within an amniotic sac.
- Anamniotes: Do not develop an amniotic sac.
Yolk Sac: Source of food for the developing embryo.
Chorion: Participates in gas exchange.
Allantois: Stores metabolic wastes and also participates in gas exchange.

Extraembryonic Membranes in Different Vertebrates

Fishes: Only the yolk sac forms. Respiration and excretion occur through direct contact with the environment.
Reptiles and Birds: Amnion protects the embryo. Yolk sac provides nourishment. Chorion facilitates gas exchange. Allantois stores wastes (mainly uric acid) and aids in gas exchange.
Mammals:
- Monotremes (echidna, platypus): Produce shelled eggs.
- Marsupials (Metatherians): Pouched mammals (no true placenta). Yolk sac provides a rudimentary connection to the mother's blood.
- Eutherians (Placental mammals): Have a placenta facilitating nutrient transfer, gas exchange, hormone secretion, and fetal protection.

Integumentary System

Integument (Skin): The outer covering of vertebrates, including mucous membranes.
Function: Forms the interface between organisms and the external environment.
Other functions:
- Protective barrier: Protects against various forms of damage.
- Cutaneous receptors: For sensation.
- Temperature regulation: Helps maintain homeostasis.
- Excretion: Through sweat.
- Vitamin D synthesis: From sunlight exposure.

Structure of Skin

Epidermis: Derived from ectoderm.
- Composed of stratified squamous/transitional epithelium (keratinized).
- Contains pigment cells and contributes to the immune system.
- Layers: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum germinativum/basale.
- Epidermal Cells: keratinocytes, melanocytes, Langerhans cells, Merkel cells.
Dermis: Contains blood vessels, nerves, hair follicles, smooth muscles, glands, and lymphatic tissue. Composed of areolar connective tissue (collagen, elastin, reticular fibers).
Hypodermis: Not part of the skin; lies below the dermis. Made up of fat, connective tissue, and larger blood vessels.

Skin Glands

Exocrine Glands: Secrete substances onto epithelial surfaces via ducts.

Classification of Unicellular Exocrine Glands

Club Cells: Elongated binucleated cells in amphibians that secrete mucus.
Granular Cells: Found in lampreys and fishes; secrete mucus in the skin.
Goblet Cells: Narrow at the apical end, wide at the base (found in bony fishes); secrete mucus.
Sacciform Cells: Secrete toxic products to repel enemies.

Types of Multicellular Glands

Sweat Glands: Eccrine and apocrine.
Sebaceous Glands: Secrete sebum.
Ceruminous Glands: Secrete cerumen.
Mammary Glands: Secrete milk.
Poison Glands: Contain toxic or repellent chemicals.

Integument of Different Vertebrates

Fishes: Alive and active epidermis at the surface, with no keratinized cells. Contains epidermal cells and unicellular glands.
Amphibians: Specialized for cutaneous respiration. Epidermis has four layers. Dermis contains fibrous connective tissue, mucus, poison glands, and chromatophores.
Reptiles: Adapted for terrestrial environments. Extensive keratinization, with fewer skin glands. Molting (Ecdysis): Periodic shedding of the skin.
Birds: Skin covered by feathers adapted for movement. Feathers are epidermal growths that form plumage. Dermis is richly supplied with blood vessels, sensory nerves, and smooth muscles.
Mammals: Multilayered system of keratinized skin, hair, and glands. Specialized structures include hair, horns, antlers, and hooves.

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Description

Test your knowledge on phylogenetic trees and cladograms, focusing on the relationships between species and the classification of chordates. This quiz covers essential concepts such as clades, monophyletic, paraphyletic, and polyphyletic groups, as well as traits like synapomorphy and autapomorphy.