Vertebrate Development I: Amphibians & Fish

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Questions and Answers

Which of the following statements about chordates and vertebrates is true?

Vertebrates are a subgroup within chordates. (correct)

Chordates do not possess a notochord.

Some vertebrates are not classified as chordates.

All chordates are vertebrates.

What is a characteristic of the tunicate during its larval stage?

It possesses vertebrae.

It does not exhibit bilateral symmetry.

It develops a complex digestive system.

It has a notochord and dorsal nerve chord. (correct)

What initiates the formation of the neural tube in vertebrate embryos?

The somites develop first.

The notochord induces the overlying ectoderm. (correct)

The presence of yolk is crucial for this process.

The embryonic membranes influence its formation.

Why do differences in development among vertebrate taxa occur?

Due to evolutionary factors, modes of reproduction, and yolk. Signup and view all the answers

What is unique about mammalian eggs compared to those of reptiles and birds?

They are small with little yolk. Signup and view all the answers

In the context of vertebrate development, what does the term 'phylotypic stage' refer to?

The stage where all vertebrate embryos exhibit significant similarity. Signup and view all the answers

Which structures flank the notochord during vertebrate development?

Somites. Signup and view all the answers

What type of symmetry is exhibited by vertebrates?

Bilateral symmetry. Signup and view all the answers

What happens to the notochord in adult vertebrates?

It degenerates completely. Signup and view all the answers

What is the primary factor influencing the mid-blastula transition in zygotic gene expression?

Ratio of DNA to cytoplasm Signup and view all the answers

What characterizes the animal hemisphere of an unfertilized egg?

Denser concentration of pigment granules Signup and view all the answers

What happens to the dorsal surface of the embryo after fertilization?

It forms at the point of sperm entry. Signup and view all the answers

During oogenesis, where are maternal mRNAs primarily localized?

Concentrated in the vegetal hemisphere Signup and view all the answers

What occurs immediately after fertilization in terms of egg structure?

The cortical rotation begins. Signup and view all the answers

Which of these statements about the animal-vegetal axis in amphibian embryos is true?

It involves a primary polarity of the egg. Signup and view all the answers

What is the increase in the rate of protein synthesis after fertilization attributed to?

Expression of maternal mRNAs Signup and view all the answers

How does the antero-posterior axis relate to the animal-vegetal axis in an amphibian embryo?

Antero-posterior axis cannot be defined without the dorso-ventral axis. Signup and view all the answers

What is the role of the notochord during neurulation?

To induce the development of the neural plate. Signup and view all the answers

What begins to happen approximately at the mid-blastula transition?

Cell movement begins to take place. Signup and view all the answers

What structure do neural crest cells develop into?

Nerves and other various structures. Signup and view all the answers

Which of the following describes the cleavage pattern in most fish eggs?

Telolecithal and discoidal meroblastic cleavage. Signup and view all the answers

What does the epiblast form during germ layer formation?

The superficial layer that aids in cell intercalation. Signup and view all the answers

Which pair of axes must be determined in vertebrate embryos?

Anterior-posterior, dorsal-ventral, and mediolateral. Signup and view all the answers

Which structure undergoes significant elongation during embryonic development of Xenopus?

The neural tube. Signup and view all the answers

What process is characterized by the inward movement of a layer of cells during gastrulation?

Ingression. Signup and view all the answers

During the development of fish, what is the first cell movement that occurs?

Epiboly of blastoderm cells over the yolk. Signup and view all the answers

What is a characteristic of the zebrafish embryo during early development?

It undergoes rapid development and remains transparent. Signup and view all the answers

What does the blastoderm form during early cleavage in fish?

A mound of cells on the yolk. Signup and view all the answers

What happens to the neural cells during convergence and extension in the epiblast?

They migrate towards the dorsal midline. Signup and view all the answers

At what developmental stage does embryonic gene expression begin in Xenopus?

At mid-blastula transition. Signup and view all the answers

What is the primary function of the amniotic shell in the development of reptiles?

Allows for gas exchange and prevents desiccation Signup and view all the answers

Which extraembryonic membrane is responsible for gas exchange in the amniote egg?

Chorion Signup and view all the answers

How do amphibians differ from reptiles in terms of embryonic development?

Amphibians remain anamniotic and do not form an amnion Signup and view all the answers

What triggers the sexual maturation and mating behavior in frogs?

Environmental changes and hormones Signup and view all the answers

Which region of the frog egg contains the majority of yolk?

Vegetal hemisphere Signup and view all the answers

During fertilization in frogs, which structure is formed when the sperm and egg pronuclei fuse?

Zygote Signup and view all the answers

What is the process called when cells move inward during amphibian gastrulation?

Involution Signup and view all the answers

What is the fate of cells found in the marginal zone of the frog blastula?

Develop into mesodermal structures Signup and view all the answers

At what stage does gastrulation begin in frog embryos?

10000-15000 cell stage Signup and view all the answers

Which germ layer is primarily responsible for forming the nervous system in frogs?

Ectoderm Signup and view all the answers

What is the role of the yolk sac in the amniote egg?

Stores nutrients for the embryo Signup and view all the answers

What major developmental event occurs as fertilization activates cleavage in frog embryos?

Establishment of the axes of the embryo Signup and view all the answers

Which of the following describes the blastocoel in the frog blastula?

A fluid-filled cavity Signup and view all the answers

Which structure forms during cleavage and is characterized as a cluster of cells before the formation of the blastula?

Morula Signup and view all the answers

Study Notes

Vertebrate Development I: Amphibians and Fish

All vertebrates are chordates, but not all chordates are vertebrates.
Chordates and echinoderms are deuterostomes.
Invertebrate chordates include lancets (e.g., amphioxus) and tunicates (sea squirts).
All chordates have a notochord and dorsal hollow nerve chord at some point in development.
Pharyngeal grooves and a post-anal tail are also chordate characteristics.
Amphioxus (lancelet) has rudimentary notochord and nerve cord structures.
Tunicates are the closest evolutionary relatives of vertebrates.
Tunicates lack vertebrae throughout their life.
Tadpole larvae have notochords and dorsal nerve chords.
During metamorphosis, the nerve cord and notochord degenerate.
Vertebrates have a similar body plan: segmented vertebral column surrounding the spinal cord, brain at the head end enclosed in a bony or cartilaginous skull, and bilateral symmetry with many paired structures.
Timing of development varies even within groups.
Somites are mesodermal tissue blocks flanking the notochord.
Differences in vertebrate development are due to evolutionary history, reproductive modes, and yolk content.
Mammalian eggs have little yolk, and the embryo is nourished first by fluids in the oviduct and then the placenta.
Reptiles, birds and mammals are amniotes, with four extra-embryonic membranes (amnion, yolk sac, allantois, and chorion).
The amniote egg allows development entirely on land.
The shell protects against desiccation and mechanical shock and allows gas exchange.
The yolk sac stores nutrients, the amnion provides a fluid-filled environment, the allantois manages nitrogenous waste and gas exchange, and the chorion interacts with the outside environment.
Fish and amphibians are anamniotic; they do not have the extra-embryonic membranes for land development.
Frog life cycle includes egg maturation, mating behavior dependent on environmental cues and hormones (e.g., estrogen), egg polarity (animal vs. vegetal hemispheres), and a vitelline membrane encased in a gelatinous coating.
Fertilization (external) involves sperm-oocyte fusion, meiotic division, and fusion of pronuclei, forming axes of the embryo.
Cleavage results in cell division with synchronous meridional and equatorial patterns, creating a blastoderm at the animal pole.
Amphibian cleavage initially divides animal and vegetal poles with a slower rate in the vegetal hemisphere and eventual 16-64 cell stage morula formation.
Germ layers (ectoderm, mesoderm, endoderm) form during gastrulation through involution, and epiboly.
Fate maps show what tissues develop from various early embryonic regions — Xenopus is a well-studied model.
In fish, the blastoderm cells cover the yolk through epiboly and create a germ ring.
The germ ring contains the epiblast and hypoplast layers.
Convergence and extension of the hypoblast form the chordamesoderm, and adjacent cells form mesodermal somites.
Germ layer formation establishes axes in the embryo.
Early development in Xenopus (and zebra fish) is largely dependent on maternal factors in the egg rather than zygotic gene expression.
Zygotic gene expression begins in mid-blastula transition.
Animal-vegetal axis is already established in the unfertilized egg.
The antero-posterior axis is roughly similar to that of the animal vegetal axis; development of the dorso-ventral axis follows fertilization.
Reorganization of cytoplasm occurs after fertilization with cortical rotation.
The middle of the grey crescent becomes the mid-dorsal point of the embryo, and this establishes the dorsal-ventral axis.
Dorso-ventral axis in zebrafish does not involve sperm entry or cortical rotation, but rather movement of maternal dorsalizing factors from the vegetal hemisphere.
Dorsally expressed signaling centers establish dorso-ventral polarity, including the formation of the Spemann organizer.
In 1924 Hans Spemann and Hilde Mangold discovered the organizer through classic transplantation experiments that induced a secondary embryo.
Mesoderm induction happens during the blastula stage at a certain time point when animal cells are competent for mesoderm-inducing signals.
Induction occurs via signaling molecules like TGF-B family members (e.g., Xnr, BMPs, Vg-1, activin).
These signaling proteins influence the specification of other genes leading to definitive features like notochord, muscle and blood development.
Patterns of mesoderm formation in the chick and mouse occur at the primitive stem stage.
Early axis formation depends on egg polarity and results are different between vertebrate groups.
VegT and nuclear β-catenin activate or contribute to Xnr gene expression in setting up the axis.

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Description

Explore the fascinating development processes of amphibians and fish in this quiz. Learn about the key characteristics of chordates, the evolutionary relationships between vertebrates and invertebrate chordates, and the changes that occur during metamorphosis. Test your understanding of vertebral structures and developmental timing.