 Gregor Mendel was a priest from the mid 19 th century who conducted experiments in his garden.  Mendel is considered the “Father of Genetics!”

 While working in his garden, Mendel wondered why different pea plants grew tall, while others were short.  Some had green seeds, others yellow.  He called all these characteristics traits.

 Mendel experimented with thousands of pea plants to understand the process of heredity – the passing down of traits through generations.  Genetics is the scientific study of heredity.

 If you look at a flower, you can see that the petals surround two structures.  The first is the Pistil. It produces eggs, the female sex cell of plants.  The second is the stamen. Stamens produce pollen – the male sex cell. It contains sperm.

 When the egg and pollen (sperm) cells join, this is called fertilization.  Pea plants are usually self-pollinating – meaning they can pollinate themselves, even when they are alone.  Mendel developed a method to cross- pollinate – meaning he moved the pollen from one plant to the pistol of another. This is called “cross pollination” or “crossed” for short.

 Mendel decided to cross plants that looked completely different to see what would happen.  He started with purebred plants. Plants that he saw that generation after generation, produced plants that looked identical to the parent plant.  He called the Parent generation the “P generation” for short.

 In one experiment, Mendel crossed pure- bred tall plants with purebred short plants.  Scientists today call these parent plants the parental generation (P generation).  All of offspring were Tall!

 The offspring generation are called “F generations.”  The “F” stands for filial – the Latin word for “daughter” and “son.”  The first generation of offspring are noted by a little number 1 after the letter “F” (F 1 ).  The second generation (from mating the F 1 ’s together) form the F 2 generation (and so forth).

 When the plants in the F 1 generation were full grown, Mendel allowed them to self- pollinate.  Surprisingly, the plants in the F 2 generation were a mix of tall and short plants!  The shortness trait had reappeared!

 Mendel counted the tall and short plants.  About 3/4ths of the plants were tall, while only 1/4 th of the plants were short.

 Mendel also crossed pea plants with other contrasting traits.  In all of Mendel’s crosses, only one form of the trait appeared in the F 1 generation.  However, in the F 2 generation, the “lost” form of the trait always reappeared in about 1/4 th of the plants!

 Mendel reached several conclusions on the basis of his experimental results.  He reasoned that individual factors, or sets of genetic “information,” must control the inheritance of traits from peas!  The factors must come in PAIRS!  One from the male parent and one from the female parent!

 The last conclusion Mendel made was that one factor in the pair can Mask or Hide the other!  In Mendel's experiments, Tallness in pea plants masked the Short pea characteristic. 

 Today, we use the word “Gene” instead of “factor.”  Alleles are the different forms of the same Gene.  Plant Height = Gene › Tall plants = allele › Short plants = allele

 Each pea plant inherits two alleles from its parents – one from the egg and one from the sperm.  A pea plant may inherit two alleles for tall stems, two alleles for short stems, or one of each.

 An organism’s traits are controlled by the alleles it inherits from its parents.  Some alleles are Dominant, while other alleles are recessive.  A Dominant allele is one whose traits ALWAYS shows up in the organism when it is present!  A recessive allele, on the other hand, is hidden by a dominant trait. It only shows up when it is ALONE!

 In Mendel’s cross for stem height, the purebred tall plants in the P generation had two alleles for tall stems.  The purebred short plants had two alleles for short stems.  The F1 plants each inherited an allele for tall stems from the tall parent and an allele for short stems from the short parent.

 When you have two genes that are different (not purebred) then you are called a Hybrid! › Name another thing you think about when you hear the word “Hybrid.” What does it mean in your example?

 Geneticists use letters to represent alleles.  A Dominant allele is ALWAYS represented with a capital letter! › Tall plants = T  A recessive allele is ALWAYS represented by a lowercase version of THE SAME LETTER OF THE DOMINANT ALLELE! › Short plants = t  This way, you always know that the “T’s” go together!

 When a plant inherits two Dominant alleles for tall stems, its alleles are written as TT.  When a plant inherits two recessive alleles for short stems, its alleles are written as tt.  When a plant inherits one allele for tall stems and one allele for short stems, its alleles are written as Tt.

 Unfortunately, the importance of Mendel’s discovery was not recognized during his lifetime.  Then, in 1900, three different scientists rediscovered Mendel’s work.  These scientists quickly recognized the importance of Mendel’s ideas.  Because of his work, Mendel is often called the Father of Genetics.