7.3 Mendelian Inheritance

Introduction

The field of genetics began in 1900 with the rediscovery of a paper published in 1866 by Gregor Johann Mendel, an Augustinian monk. Mendel was the first person who successfully explained the mode of inheritance of traits from one generation to the next through his experiments on pea plants. The mode of inheritance according to the principles proposed by Mendel is known as Mendelian inheritance. Mendel's work laid the foundation for the science of inheritance, which is why he has been titled as the "Father of Genetics."

Definition

Mendelian inheritance is the mode of inheritance of traits from one generation to the next according to the principles proposed by Gregor Johann Mendel.

Main Idea

• The field of genetics began in 1900 with the rediscovery of a paper published in 1866 by Gregor Johann Mendel.
• Mendel was the first person who successfully explained mode of inheritance of traits from one generation to the next through his experiments on pea plants.
• The mode of inheritance according to the principle proposed by Mendel is known as Mendelian inheritance.
• Mendel's work laid the foundation for the science of inheritance, which is why he has been titled as the "Father of Genetics".
• First, he developed true-breeding plants, which consistently produced offspring with the same traits after self-fertilization.
• This was achieved by repeated self-fertilization over successive generations.
• Mendel worked with seven pairs of contrasting traits, creating true-breeding plants for each.
• Mendel then carried out hybridization, where he cross-fertilized plants with different traits.
• For example, he crossed a round-seed plant with a wrinkled-seed plant to study a single trait (monohybrid cross) and a round, yellow-seed plant with a wrinkled, green-seed plant to study two traits (dihybrid cross).
• A monohybrid cross involves parents differing in one trait, while a dihybrid cross involves parents differing in two traits.
• Mendel ensured specific matings of different pea plants by removing the stamen of one plant and transferring pollen using a paintbrush.
• By analyzing the inheritance of one, two, or three traits at a time, Mendel formulated what are now known as Mendel's laws of inheritance.

Core Concept

Mendel's Experiments

Seven Pairs of Contrasting Traits in Pea Plant

Detailed Explanation

1. Gregor Johann Mendel

• Mendel was an Augustinian monk.
• He published his paper in 1866.
• His work was rediscovered in 1900.
• He is titled as the "Father of Genetics".

Simple explanation: Mendel was a monk who discovered the basic principles of inheritance by experimenting with pea plants.

2. True-Breeding Plants

First, he developed true-breeding plants, which consistently produced offspring with the same traits after self-fertilization. This was achieved by repeated self-fertilization over successive generations.

Simple explanation: True-breeding plants always produce offspring with the same trait. For example, a true-breeding round-seed plant always produces round-seed offspring.

3. Seven Pairs of Contrasting Traits

Mendel worked with seven pairs of contrasting traits, creating true-breeding plants for each.

Examples:

• Seed shape: Round vs. Wrinkled
• Seed color: Yellow vs. Green
• Flower color: Purple vs. White
• Stem length: Tall vs. Short

Simple explanation: Mendel studied seven different traits, each with two contrasting forms.

4. Hybridization

Mendel then carried out hybridization, where he cross-fertilized plants with different traits.

Examples:

• He crossed a round-seed plant with a wrinkled-seed plant to study a single trait (monohybrid cross).
• He crossed a round, yellow-seed plant with a wrinkled, green-seed plant to study two traits (dihybrid cross).

Simple explanation: Hybridization is crossing two plants with different traits to see how those traits are inherited.

5. Types of Crosses

Simple explanation: A monohybrid cross looks at one trait at a time. A dihybrid cross looks at two traits at a time.

6. Mendel's Technique

Mendel ensured specific matings of different pea plants by:

• Removing the stamen of one plant (to prevent self-fertilization).
• Transferring pollen using a paintbrush.

Simple explanation: Mendel controlled which plants mated by removing the male parts of one plant and manually transferring pollen from another plant.

7. Mendel's Laws of Inheritance

By analyzing the inheritance of one, two, or three traits at a time, Mendel formulated what are now known as Mendel's laws of inheritance.

Mendel's laws include:

• Law of Segregation
• Law of Independent Assortment

Simple explanation: Mendel's experiments led to the discovery of the basic laws of inheritance.

Summary of Mendelian Inheritance

Intermediate Level

Mendelian inheritance is the mode of inheritance of traits according to the principles proposed by Gregor Johann Mendel.

Key points:

• Mendel was an Augustinian monk.
• He published his paper in 1866.
• His work was rediscovered in 1900.
• He is titled as the "Father of Genetics".
• He developed true-breeding plants.
• He worked with seven pairs of contrasting traits.
• He carried out hybridization (cross-fertilization).
• He performed monohybrid and dihybrid crosses.
• He formulated the Law of Segregation and the Law of Independent Assortment.

Seven pairs of contrasting traits:

Important Points

• - The field of genetics began in 1900 with the rediscovery of a paper published in 1866 by Gregor Johann Mendel.
• - Mendel was the first person who successfully explained mode of inheritance of traits from one generation to the next through his experiments on pea plants.
• - The mode of inheritance according to the principle proposed by Mendel is known as Mendelian inheritance.
• - Mendel's work laid the foundation for the science of inheritance, which is why he has been titled as the "Father of Genetics".
• - First, he developed true-breeding plants, which consistently produced offspring with the same traits after self-fertilization.
• - This was achieved by repeated self-fertilization over successive generations.
• - Mendel worked with seven pairs of contrasting traits, creating true-breeding plants for each.
• - Mendel then carried out hybridization, where he cross-fertilized plants with different traits.
• - For example, he crossed a round-seed plant with a wrinkled-seed plant to study a single trait (monohybrid cross).
• - He crossed a round, yellow-seed plant with a wrinkled, green-seed plant to study two traits (dihybrid cross).
• - A monohybrid cross involves parents differing in one trait, while a dihybrid cross involves parents differing in two traits.
• - Mendel ensured specific matings of different pea plants by removing the stamen of one plant and transferring pollen using a paintbrush.
• - By analyzing the inheritance of one, two, or three traits at a time, Mendel formulated what are now known as Mendel's laws of inheritance.

Remember

• - Mendel = Father of Genetics
• - Organism = pea plant
• - True-breeding plants = always produce same trait
• - Seven pairs of contrasting traits
• - Hybridization = cross-fertilization
• - Monohybrid cross = one trait
• - Dihybrid cross = two traits
• - Mendel's laws = Law of Segregation, Law of Independent Assortment
• - Mendel called genes "factors" or "elements"

Common Mistakes

• 1. Thinking Mendel worked with animals.
• - Mendel worked with pea plants.
• 2. Forgetting the number of traits Mendel studied.
• - Mendel studied seven pairs of contrasting traits.
• 3. Confusing monohybrid and dihybrid crosses.
• - Monohybrid = one trait.
• - Dihybrid = two traits.
• 4. Thinking Mendel knew about DNA.
• - Mendel did not know about DNA. He called genes "factors" or "elements".
• 5. Believing Mendel's work was immediately accepted.
• - Mendel's work was largely ignored until 1900, when it was rediscovered.
• 6. Mixing up the terms "true-breeding" and "hybridization".
• - True-breeding = always produces same trait.
• - Hybridization = cross-fertilization of different traits.
• 7. Forgetting that Mendel removed the stamen.
• - Mendel removed the stamen to prevent self-fertilization and control matings.

Quick Revision

Seven Pairs of Contrasting Traits

60-Second Revision

• Mendel = Father of Genetics
• **Organism** = pea plant
• True-breeding plants = always produce same trait
• Seven pairs of contrasting traits
• Hybridization = cross-fertilization
• Monohybrid cross = one trait
• Dihybrid cross = two traits
• Mendel's laws = Law of Segregation, Law of Independent Assortment
• Mendel called genes "factors" or "elements"
• Warning: Do not confuse monohybrid (one trait) with dihybrid (two traits) crosses. Mendel worked with pea plants, not animals. His work was rediscovered in 1900.