The “father of genetics”, Gregor Mendel, was a Monk who lived in the 19th century.He was the first to carry out experiments and describe how genes are passed down from parent to offspring, carrying out experiments using pea plants.

Mendel studied seven of their characteristics:

  • The shape of the pod
  • The colour of the pod
  • The shape of the seed
  • The colour of the seed
  • The colour of the flower
  • The position of the pod and the flower
  • The length of the stem

Important definitions in Genetics

Before we get into the details of Mendelian Genetics, let us point out and explain important terms that will be used repetitively throughout this course.

  1. Gene: a segment of the DNA that codes for a protein and/or RNA
  2. Locus: the location of a particular gene on a chromosome
  3. Allele: An allele is a variant of a gene. It can be dominant or recessive
  4. Dominant allele: this is an allele that will be expressed as a dominant trait. A dominant trait is one that is expressed always if it is present
  5. Recessive allele: this is an allele that will be expressed as a recessive trait. A recessive trait will only be expressed in the absence of a dominant trait.
  6. Co dominance: this is an exception to the 'dominant-recessive allele' theory. In this case, the two alleles present are both dominant and both of them will be expressed in the cell individually. For example, a person with blood group AB has the genes for both A and B antigens. As they are both dominant genes, both the 'A' antigen and 'B' antigen will be expressed on the surface of the red blood cell (see illustration below). Details on blood groups are discussed in

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