Foundations of Heredity: Mendel, Sutton, Morgan, DNA & RNA

Gregor Mendel's Contributions to Genetics

Note: This section details the scientific method applied to the study of inheritance.

Mendel's Scientific Method in Inheritance

Formulation of the Problem:

How are characteristics passed down from parents to offspring?

Hypothesis:

Sex cells contain structures responsible for the transmission of characters.

Experiment (Proof):

Crosses were made with purebred pea plants. In Cross 1, one character varied while six others remained constant.

Results and Conclusions:

Cross 1: All F1 generation individuals expressed the dominant character. In the F2 generation, the phenotypic ratio was 3:1.

Conclusions: Gametes contain factors responsible for character transmission, and each character is determined by two factors.

Key Principles of Mendelian Inheritance

Law of Uniformity (First Law):

When crossing two purebred individuals differing in a particular character, the first-generation (F1) hybrids are phenotypically similar.

Law of Segregation (Second Law):

During gamete formation, each allele of a pair separates from the other to determine the genetic constitution of the final gamete.

Law of Independent Assortment (Third Law):

When purebred individuals differing in two or more characters are crossed, each character is transmitted to the next generation independently.

Mendel's Enduring Legacy in Genetics

Mendel established the concept of discrete hereditary units (genes) and their patterns of inheritance.

Walter Sutton and the Chromosomal Theory of Inheritance

Walter Sutton's Research on Meiosis and Heredity

Research Focus:

The relationship between meiosis and inheritance.

Central Question:

What is the relationship between meiosis and inheritance?

Hypothesis:

If chromosomes within gametes contain Mendelian factors, they allow for the transmission of characters.

Experiment:

Observation of meiosis in grasshoppers.

Results and Conclusions:

Chromosomes exist in pairs and are the bearers of heredity.

Thomas Morgan's Gene Mapping Discoveries

Thomas Morgan's Research on Gene Location and Distribution

Research Focus:

Location and distribution of genes on chromosomes.

Central Question:

How are genes distributed on chromosomes?

Hypothesis:

If genes are distributed linearly on chromosomes, this allows for the inheritance of characters.

Experiment:

Crosses were performed with Drosophila melanogaster (fruit flies).

Results and Conclusions:

Genes are located on chromosomes, including sex-linked characters.

Nucleic Acids: DNA and RNA Fundamentals

Deoxyribonucleic Acid (DNA)

• Full Name: Deoxyribonucleic acid
• Bases: Adenine, Guanine, Thymine, Cytosine
• Sugar: Deoxyribose
• Primary Location: Nucleus
• Function: Stores genetic information

Ribonucleic Acid (RNA)

• Full Name: Ribonucleic acid
• Bases: Uracil, Guanine, Adenine, Cytosine
• Sugar: Ribose
• Primary Location: Cytoplasm
• Function: Involved in processing and transmitting genetic information (e.g., protein synthesis)