Mendel and Genetics

Gregor Mendel and the Foundations of Genetics

Goal: Understand Mendel’s work and why it was important for genetics.

1. Background

• Genes are sections of DNA on a chromosome, each coding for a specific protein.

• Alleles are different versions of a gene:

  • Dominant allele: expressed even if only one copy is present (e.g., purple flowers in peas).

  • Recessive allele: only expressed if two copies are present (e.g., yellow flowers in peas).

2. Mendel’s Experiments

• Mid-1800s, Gregor Mendel, a monk, carried out thousands of breeding experiments on pea plants.

• He studied different characteristics, such as:

  • Flower color

  • Pod shape

Key discoveries:

1. Characteristics are inherited in discrete units (now called genes) rather than being blended.

2. Some characteristics can be masked and reappear in later generations → recessive alleles.

3. Dominant alleles mask recessive ones in heterozygotes.

3. Publication and Initial Neglect

• Mendel published his work in a scientific paper.

• At the time, many scientists still believed in blended inheritance.

• Mendel’s work was largely ignored during his lifetime.

4. Rediscovery and Significance

• Late 1800s: Scientists studying chromosome behavior during cell division noticed patterns similar to Mendel’s units.

• Early 1900s: Mendel’s units were renamed genes, understood to be located on chromosomes.

• Mid-1900s: Discovery of DNA structure and gene function explained how inheritance works at a molecular level.

✅ Key Takeaways

• Mendel showed that inheritance is predictable and follows specific patterns.

• Dominant vs recessive alleles explain why some traits skip generations.

• Mendel’s work laid the foundation for modern genetics.