Introduction to Classical Genetics

Mendelian Inheritance, Biological Sex and Reproduction

May 24, 2009 Barbara Melville

Classical genetics is the oldest field within genetic science, and an essential foundation for several other disciplines.

Classical genetics is a field concerned with traits and how they are inherited. In humans, traits such as hair color, height and nose shape are transmitted down through generations. Individuals may find it interesting to look through family photographs to see which observable traits (phenotypes) have recurred.

A basic understanding of traits and inheritance doesn’t require knowledge of molecular genetics, the sub-discipline concerned with genes at molecular level. Cell division and chromosomes are relevant in classical genetics, but a deep understanding of cell function isn’t required to grasp the basics of inheritance.

Gregor Mendel and Inheritance

The term “Mendelian genetics” refers to Gregor Mendel’s contributions to the science of heredity, and is considered a foundation of classical genetics. Mendel is best known for observing inheritance via a series of hybridization experiments with pea plants during the 19th century.

Mendel’s conclusions were astounding for his time, and mostly accurate. He suggested that an organism receives half of its genetic material from each biological parent. He also introduced the idea of dominant and recessive genes, which was later shown to be more complex than he proposed.

Biological Sex and Reproduction

Biological sex refers to an organism being male or female. In humans, there are notable differences between males and females, such as sexual organs, body hair and body fat. Unlike humans, some organisms actually change their biological sex under certain environmental conditions.

Traits cannot be transmitted without reproduction. Many animals require gametes (sex cells) from a male and female in order to produce offspring. In humans, reproduction takes place when the female egg cell is fertilized by the male sperm cell. The fertilized egg then has the potential to develop into a fetus.

Not all organisms reproduce this way. Bacteria, for example, are prokaryotic organisms that reproduce asexually by a type of cell division called binary fission. Some plants are hermaphrodites, meaning they are both male and female, and able to reproduce themselves.

For more information on the different areas within classical genetics, read the classical genetics section on the DNA from the Beginning website. Read Basic Cell Biology for Understanding Genetics, which includes the basics of eukaryotic cells, prokaryotic cells and cell division.

Sources

Genes, Alleles and Sources of New Inherited Variation (pp80-84); Genetics, Evolution and Biodiversity, published by Nelson Thornes in 2004, authors: Adds, J. et al.

Classical Genetics, Encyclopaedia Britannica website, accessed: 24th May 2009, no author specified.

Classical Genetics, DNA from the Beginning website, accessed: 24th May 2009, no author specified.

The copyright of the article Introduction to Classical Genetics in Genetics & Evolution is owned by Barbara Melville. Permission to republish Introduction to Classical Genetics in print or online must be granted by the author in writing.

Sperm Cells