Biology Figures: Miescher, Flemming, Morgan

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Questions and Answers

What did Miescher name the substance he found within cell nuclei?

Chromatin

Nuclein (correct)

Cytoplasmic Material

Nucleic Acid

According to Miescher’s research, which element did he believe nuclein lacked?

Carbon

Phosphorus

Oxygen

Sulfur (correct)

Which of the following was NOT stated as a criterion for a molecule to be a carrier of inheritance?

Must be physically stable

Must have the ability to mutate (correct)

Must be passed on to the next generation

Must be duplicated and equally divided

Why was DNA not considered the carrier of genetic information during Miescher's time?

Because proteins were known to contain more information Signup and view all the answers

What is the primary purpose of forward genetic screening in this experimental design?

To isolate a specific gene based on phenotype Signup and view all the answers

What role do the mutated genes play in the growth of spores on minimal media?

They disrupt amino acid biosynthesis pathways Signup and view all the answers

What was hypothesized regarding the function of each gene based on this experimental design?

Each gene produces a unique protein or enzyme Signup and view all the answers

In the context of this experiment, what can be inferred about wildtype spores?

They can synthesize all amino acids and grow on both media types Signup and view all the answers

What is the conclusion drawn from the observations regarding the mutated gene?

The mutated gene is responsible for at least one specific amino acid synthesis Signup and view all the answers

What term did Walther Flemming coin to describe the behavior of chromosomes during cell division?

Mitosis Signup and view all the answers

Which scientist discovered that genes close together on chromosomes are often inherited together?

Thomas Morgan Signup and view all the answers

What was the significance of Beadle and Tatum's choice of the Neurospora model organism in their experiment?

They are haploid and can produce ascospores. Signup and view all the answers

Which of the following statements about chromosomes is correct?

Chromosomes are only visible during cell division. Signup and view all the answers

How did Hermann Muller contribute to the understanding of gene inheritance?

He used X-rays to induce mutations that could be inherited. Signup and view all the answers

What did the results of Thomas Morgan's experiments with fruit flies demonstrate about eye color?

Eye color is genetically linked to sex in fruit flies. Signup and view all the answers

What does DNA's ability to duplicate and equally divide indicate about its role?

It is the underlying molecule of inheritance. Signup and view all the answers

What was a key finding from Beadle and Tatum's experiment with Neurospora?

Genes can be linked to specific biochemical pathways. Signup and view all the answers

Which of the following best describes the process of forward genetic screening?

Identifying responsible genes through changes in phenotype. Signup and view all the answers

How did Beadle and Tatum conduct their forward genetic screening?

By crossing wildtype with mutagenized conidia. Signup and view all the answers

What was the primary conclusion of Beadle and Tatum's experiment in relation to the one gene:one enzyme hypothesis?

Each gene produces a distinct protein, often functioning as an enzyme. Signup and view all the answers

Which of the following is an exception to the one gene:one enzyme hypothesis?

Some genes direct the synthesis of tRNAs and rRNAs. Signup and view all the answers

What does the term 'transformation' refer to in a molecular biology context?

The introduction of DNA from the environment into a bacterial cell. Signup and view all the answers

What was a significant observation made during Griffith's experiment with the pneumonia-causing bacteria?

The R strain could be transformed into the S strain when mixed with heat-killed S strain. Signup and view all the answers

What role does the polysaccharide coat play in the virulence of the S strain in Griffith's experiment?

It prevents immune cells from recognizing and attacking the bacteria. Signup and view all the answers

Which of the following best explains Griffith's conclusions regarding genetic material?

Genetic traits can be transferred between different bacterial strains. Signup and view all the answers

What was the hypothesis behind Avery, Macleod and McCarty's experiment?

If DNA was the molecule of inheritance, it would be the molecule transferred to R cells. Signup and view all the answers

What observation led to the conclusion that DNA was the transforming substance in Avery, Macleod and McCarty's experiment?

No transformation occurred when DNA was absent. Signup and view all the answers

Why is Hershey and Chase's experiment often referred to as the blender experiment?

A blender was used to separate protein coats from DNA after infection. Signup and view all the answers

What was the main finding of Hershey and Chase's experiment regarding the genetic material of bacteriophages?

DNA was confirmed as the genetic material injected into E. coli. Signup and view all the answers

What method did Avery, Macleod and McCarty employ to determine which component of the S strain was responsible for transformation?

They selectively destroyed different biomolecules to assess the impact on transformation. Signup and view all the answers

What radioactive isotopes were used in Hershey and Chase's experiment to label the components of bacteriophages?

35S and 32P Signup and view all the answers

What significant conclusion can be drawn from the research of Avery, Macleod and McCarty?

DNA is the molecule responsible for the transfer of genetic information. Signup and view all the answers

What does the transformation of non-virulent R strain into virulent S strain suggest?

Genetic information can be shared between bacterial strains. Signup and view all the answers

Study Notes

Friedrich Miescher

Discovered nuclein, a substance found in the nuclei of cells.
Nuclein was found to contain large amounts of phosphorus, but no sulfur.
Salmon sperm, rich in nuclei, was used to purify nuclein.
Nuclein was composed of C, N, H, O, and P, the same components found in DNA.

Walther Flemming

Improved microscope resolution, allowing for detailed observation of cell division.
Used a basophilic dye to stain the material inside the cell nucleus, which he termed chromatin.
Observed chromatin collecting into thread-like structures during cell division, which he termed chromosomes.
Coined the term mitosis to describe the behavior of chromosomes during cell division.
Found that daughter cells contained a set of chromosomes identical to the parent cell, suggesting DNA as the molecule of inheritance.

Thomas Morgan

Studied fruit flies due to their rapid reproductive cycle.
Observed that the inheritance of eye color in fruit flies did not align with Mendel's Law of Dominance.
Discovered genetic linkage, where genes close together on chromosomes are often inherited together, contradicting Mendel's Law of Independent Assortment.
Proposed that sex could play a role in inheritance, introducing the concept of sex-linked genes.

Herman Muller

Collaborated with Morgan to induce mutations in fruit fly genomes using X-rays.
Demonstrated that genes could be inherited.
Showed that genes could be mutated by chemical and radiological means, and that those mutated genes could be passed onto offspring.

Beadle and Tatum

Used the model organism Neurospora (bread mold) for their experiment.
Neurospora is a haploid organism that rapidly mates with mutated strains, allowing for easy observation of genetic mutations.
Proposed the “one gene, one enzyme” hypothesis, stating that each gene is responsible for creating a different protein, most of which function as enzymes
Conducted a forward genetic screen to isolate a specific gene by introducing mutations.
Found that the mutated gene was responsible for synthesizing specific amino acids, supporting their hypothesis.
Demonstrated that genes code for proteins.

Forward and Reverse Genetic Screens

Forward genetic screening: Phenotype → Gene
- Random mutagenesis.
- Isolation of a mutant phenotype and study of its gene.
- Identifies responsible genes by observing phenotypic changes.
Reverse genetic screening: Gene → Phenotype
- Targeted mutagenesis.
- Mutations of a known gene to observe its governing phenotype.
- Observes changes in phenotype.

Beadle and Tatum's Experiment

A forward genetic screen, where mutations were introduced and screened for a specific phenotype.
Mutagenized conidia were crossed with wild-type to produce ascospores.
Observed ascospores that lost the ability to synthesize specific amino acids.

The “One Gene, One Enzyme” Hypothesis

Each gene in an organism is responsible for creating a different protein, most of which function as enzymes.
Exception: Not all genes code for enzymes. Some code for RNA molecules like tRNAs (transfer RNAs) and rRNAs (ribosomal RNAs).

Griffith's Experiment

Studied the pathology of bacteria that cause pneumonia.
Identified two strains of bacteria:
- R strain (non-virulent) could be recognized by immune cells.
- S strain (virulent) was not recognized by immune cells due to its polysaccharide coat.
Discovered transformation: uptake of foreign DNA from the environment incorporated into bacterial DNA.
Mixing heat-killed S cells with living R cells resulted in the uptake of DNA by R cells.
Concluded that heritable traits could be exchanged between bacterial strains.
Significant because it suggested that genetic information could be transferred between organisms.

Avery, Macleod, and McCarty's Experiment

Hypothesis: DNA is the molecule of inheritance.
Experimental design: Elimination of other components (proteins, RNA) by using enzymes to see if transformation still occurred.
Observed that transformation only occurred when DNA was present.
Concluded that DNA was the molecule responsible for transformation.
This experiment provided crucial evidence that DNA is the genetic material.

Hershey and Chase's Blender Experiment

Hypothesis: Is DNA or protein the genetic material of bacteriophages?
Experimental design: Used radioactive isotopes to label the protein coat (35S) and DNA (32P) of bacteriophages.
Infection of bacteria with labeled bacteriophages followed by blending and separation.
Observed radioactivity in the bacteria only in the presence of 32P (DNA).
Concluded that DNA, not protein, was the genetic material of the bacteriophages.
This experiment provided strong evidence that DNA is the molecule of inheritance.

Significance of Hershey and Chase's Research

Demonstrated that DNA is the genetic material transferred from bacteriophages to bacteria.
Strengthened the evidence that DNA, not protein, is responsible for inheritance.
Often referred to as the “blender experiment” due to the use of a blender to separate the bacteriophage components.

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Description

Explore the contributions of Friedrich Miescher, Walther Flemming, and Thomas Morgan to the field of biology. This quiz covers essential discoveries related to nuclein, chromatin, chromosomes, and inheritance using fruit flies as a model organism. Test your knowledge on these pivotal scientists and their groundbreaking work in genetics and cell biology.