Genetics and Model Organisms Quiz

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Questions and Answers

What was the primary contribution of Thomas Hunt Morgan's experiments with fruit flies?

Proving that all traits are determined by environmental factors.

Developing the first genetically modified organisms.

Establishing traits as located on chromosomes. (correct)

Introducing the concept of genetic engineering.

Which phenomenon did Thomas Hunt Morgan discover related to chromosome behavior?

Transcription

Mutation

Crossover (correct)

Mitosis

Why is Drosophila melanogaster considered a model organism?

It has a long lifespan and is commercially valuable.

It can produce many generations quickly and shows clear mutations. (correct)

It is resistant to all diseases and pests.

It has a complex genome requiring extensive resources.

What is the primary reason for using Caenorhabditis elegans in research?

Its simplicity in structure. Signup and view all the answers

What percentage of the genes in Caenorhabditis elegans have human homologues?

36% Signup and view all the answers

What is the approximate number of genes found in the genome of the fruit fly?

14,000 Signup and view all the answers

What does Arabidopsis thaliana serve as a model organism for?

Molecular biology in plants. Signup and view all the answers

How many somatic cells does a mature Caenorhabditis elegans have?

959 Signup and view all the answers

How long does it typically take Arabidopsis thaliana to produce thousands of shoots?

8-10 weeks Signup and view all the answers

What is the approximate length of the Caenorhabditis elegans genome?

100 million base pairs Signup and view all the answers

What forms can adult Caenorhabditis elegans take?

Males and hermaphrodites Signup and view all the answers

What was the significance of sequencing the fruit fly genome in 2000?

It allowed researchers to study gene function in humans. Signup and view all the answers

What is the role of the cuticle in Caenorhabditis elegans?

To protect the organism Signup and view all the answers

What major genetic topics were elucidated by Morgan's research?

Inheritance patterns and linkage of characters on chromosomes. Signup and view all the answers

What is the approximate lifespan of a Caenorhabditis elegans adult?

2-3 weeks Signup and view all the answers

What key advantage does the transparency of Caenorhabditis elegans provide in research?

Facilitates observation of developmental processes Signup and view all the answers

What is the maximum magnification achievable with a conventional light microscope?

1,000 X Signup and view all the answers

Which of the following microscopes has the highest resolving power?

Transmission electron microscope Signup and view all the answers

What is the resolving power of the human eye?

0.1 mm Signup and view all the answers

Which component is NOT part of the mechanical system of a conventional optical microscope?

Eyepiece Signup and view all the answers

What value does NA (Numerical Aperture) represent in microscopy?

The refractive index and angle of the light cone Signup and view all the answers

Which factor primarily determines the resolution in microscopy?

Wavelength of light used Signup and view all the answers

What type of tissue can primarily be observed using optical microscopy?

Epithelial tissue Signup and view all the answers

Which of the following statements about electron microscopy is true?

It offers much higher magnification than light microscopy. Signup and view all the answers

What did Antoni van Leeuwenhoek refer to the microscopic organisms he observed?

Animalcules Signup and view all the answers

Which of the following was NOT a component of cell theory as formulated in 1839?

Cells are capable of spontaneous generation. Signup and view all the answers

Which cell type is characterized by the absence of a nucleus?

Prokaryotic cells Signup and view all the answers

Who are credited with the formulation of cell theory?

Matthias Schleiden and Theodor Schwann Signup and view all the answers

What is the main structural difference between prokaryotic and eukaryotic cells?

Eukaryotic cells have a more complex genome structure. Signup and view all the answers

What significant role did Rudolf Virchow play in the development of cell theory?

He proposed that cells arise from pre-existing cells. Signup and view all the answers

What type of organisms do eukaryotic cells include?

Protozoa, plants, fungi, and animals Signup and view all the answers

How long ago did life emerge on Earth according to the information provided?

3.8 billion years ago Signup and view all the answers

What is the primary purpose of using paraffin in histological processing?

To provide structural support for fine sectioning Signup and view all the answers

Which type of dye is primarily used to stain acidic substances in tissue?

Hematoxylin Signup and view all the answers

What is the main characteristic of resins compared to paraffin in histology?

Resins are harder and facilitate finer cuts than paraffin Signup and view all the answers

What is the purpose of the cryostat in histological techniques?

To maintain tissues at a low temperature during cutting Signup and view all the answers

What technique allows the visualization of proteins without the need for fixation or staining?

Green Fluorescent Protein (GFP) Signup and view all the answers

Which of the following is NOT a basic dye used in optical microscopy?

Eosin Signup and view all the answers

What does the rate of fluorescence recovery in FRAP indicate?

The rate of protein movement within the cell Signup and view all the answers

In FRET, what is required for the interaction between two proteins to be detected?

They must absorb and emit light at different wavelengths Signup and view all the answers

What is the typical thickness range for sections made with a microtome for optical microscopy?

Between 3-5 mm Signup and view all the answers

How are freeze-fixed samples typically sectioned?

Using a cryostat while maintaining a low temperature Signup and view all the answers

How does confocal microscopy improve the detail of images acquired from samples?

By focusing laser light onto a defined spot at a specific depth Signup and view all the answers

What allows for the direct visualization of cells in liquid mediums without significant processing?

The absence of fixation or sectioning steps Signup and view all the answers

What is the purpose of the pinhole in the optical pathway of a confocal microscope?

To filter out light from out-of-focus areas Signup and view all the answers

What method can be used to visualize 3D objects using confocal microscopy?

Scanning several optical planes and stacking them Signup and view all the answers

Which aspect of protein visualization does the GFP revolution primarily focus on?

Live imaging of proteins without fixation Signup and view all the answers

What type of analysis does FRET specifically enable?

Detection of protein interactions based on proximity Signup and view all the answers

Study Notes

Unit 1: Overview of the Cell and Cell Research

Biology is the study of the composition, development, functioning, links, and distribution of living things.
Cells are the fundamental units of living beings, capable of independent reproduction.
Cell biology analyzes cell structure, function, components, interactions, and properties. It draws on genetics, biochemistry, and immunology among other areas of knowledge.
Molecular biology focuses on the processes of living beings from a molecular point of view. It examines macromolecules like nucleic acids (DNA, RNA) and proteins.
The fundamental difference is the focus. Cell biology focuses on how cellular systems work, cell regulation, and structure. Molecular biology focuses on the functions of molecular structure (especially in relation to DNA and RNA.)

1.1 Origin and evolution of cells

The cell is the basic structural, functional, and biological unit of all known organisms.
Robert Hooke (1635-1703) first described cells in cork.
Antoni van Leeuwenhoek (1632-1723) observed protozoa, blood cells, sperm, and bacteria, calling them "animalcules".
Cell theory (formulated in 1839) states: all living things are made of cells; the cell is the basic unit of structure and organization in organisms; cells come from pre-existing cells; heredity information passes from cell to cell.

1.2 Cells as experimental models

Unicellular models: Escherichia coli and Yeast
Multicellular models: Arabidopsis thaliana, Caenorhabditis elegans, Drosophila melanogaster, Danio rerio, Mus musculus

1.3 Cell biology instruments (a)

Optical microscopy (magnification: 1000x, resolution: 0.2 µm)
Electron microscopy (magnification 150,000 - 200,000x, resolution 1-2 nm)
Super-resolution Microscopy

1.3 Cell biology instruments (b)

Specimen preparation
Flow cytometry
Subcellular separation
Growth of animal cells in culture
Virus

Specimen preparation

Histological processing: Fixation, Tissue embedding, Sectioning, Staining

Fixation

Physical: Cryofixation (exposing tissue to temps below -70°C)
Chemical: using chemicals to stabilize macromolecules in the tissue

Tissue embedding

Paraffin: used for optical microscopy, consisting of long-chain hydrocarbons.
Resins: used for electron microscopy, often harder than paraffin, and capable of finer cuts

Sectioning

Histological sections are made in a microtome (3-5 µm) or ultra-microtome (10-100 µm)
Freeze-fixed samples are thicker (6-8 µm) and processed in a cryostat

Stainings

Dyes with different affinities are used in optical microscopy, dependent on the chemical composition.
Examples include hematoxylin (basic), eosin (acidic), and various others.
In electron microscopy, high molecular weight molecules like heavy metals (uranium acetate or lead citrate) are often used to improve contrast.

Immunohistochemical techniques

Purpose: to identify a specific protein in a tissue section, using specific antibodies.
Direct method: Primary antibody is conjugated to the visualizing agent.
Indirect method: Primary antibody is not conjugated, a secondary antibody is used for visualization.

Flow cytometry

A technique for analyzing the number, size, and complexity of a cell suspension.
Used to quantify cells and isolate populations.
Components include: Fluidic sample transport, Optical laser illumination, Electronic detector.
Measures forward scatter (FSC) for size and side scatter (SSC) for complexity.

Subcellular separation

Methods to isolate specific organelles and subcellular particles.
Enzymatic methods (like lysozyme) for cells with walls
Physical methods (like osmotic shock or mechanical grinding)

Differential centrifugation

Used to separate different cellular components based on size and density.

Density gradient centrifugation

A method to separate organelles by sedimentation based on density.
Utilizes sucrose or cesium chloride solutions to separate components as bands.

Equilibrium separations

Separation of components based on their exact density matching the surrounding medium in the gradient.

Cell cultures

Isolation and maintenance of cells in lab conditions for study.
Advantages over intact organisms: greater control over experimental conditions.
Cultured cells can be genetically homogeneous (clones), which simplifies research.

Animal cultures

Tissue dispersion to establish primary cultures.
Cells grow to cover the dish.
Cells can be removed and replated (secondary cultures)
Some cells (like fibroblasts) have limited growth potential (passages)

Immortal cells

Derived from tumors, they can proliferate indefinitely.
Examples include HeLa cells (from a cervical cancer biopsy).

Cultured cells: media

Necessary: salts, glucose, amino acids, vitamins, and growth factors.
Maintaining oxygen levels (5% CO2 and 95% O2) at 37°C is crucial for optimal growth.

Viruses

Require a host cell (animal, plant, fungal, or bacterial) for their lifecycle.
Cultivated in cell cultures to study their roles in cell biology.

Other models

A. thaliana: used in plant molecular biology, studies of plant development and stress response.
D. melanogaster (fruit fly): used in analysis of animal development, differentiation, and genetics, especially in relation to cancer.
D. rerio (zebrafish): used for analysis of vertebrate development, neurological development, and regeneration.
Mus musculus (mouse): used for comparative studies with humans to study genetics, and for testing and developing therapies for humans (neuroscience, pharmacology, and physiology).

Additional Information: Model Organisms

Today's cells all descend from a common ancestor.
Studying one organism's features provides valuable insights into other organisms, including humans.
Some organisms present advantages for detailed study in a lab environment. (easy growth, short life-span, transparency, or easily available genome information)
The choice of an organism depends on the research question being addressed. Factors like the ability to maintain, manipulate, and cultivate the organism are critical decisions.

The choice of model organisms

Selecting a suitable model organism is crucial
Finding the right organism
Developing appropriate techniques

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Description

Test your knowledge on the contributions of Thomas Hunt Morgan and the significance of model organisms like Drosophila melanogaster and Caenorhabditis elegans. Explore their genetics and roles in research, including genome sequencing and phenotypic variations. Understand why these organisms are pivotal in the field of genetics.