A.  Basic Terminology
           1.  Gene - segment of DNA coding for the production of a protein product; known as the functional unit of DNA

           2.  Homologous Chromosomes - chromosomes with the same size, shape, and structure; they also contain the same genes at the same locations

               

           3.  Locus - location on a chromosome where the specific version of a gene is found

           4.  Genetics - study of the patterns of inheritance

           5.  Inheritance - the manner in which characteristics are passed from parents to offspring

     B.  Gregor Mendel
           1.  Background - Austrian Monk who is known as the Father of Modern Genetics
               a.  1866 - published a model of inheritance
               b.  proposed that organisms have a pair of "particles" governing each inherited trait

           2.  Pea Plants - organism that Mendel used in his genetic experiments
               a.  Reasons for Using Pea Plants:
                    1)  Small
                    2)  Inexpensive
                    3)  Short Generation Time
                    4)  Contain both male and female parts
                b.  Traits of Pea Plants:
                    1)  Seed Texture
                    2)  Seed Color
                    3)  Flower Color
                    4)  Flower Position
                    5)  Stem Length
                    6)  Pod Shape
                    7)  Pod Color

           3.  Generations:
                a.  Parental Generation = P₁ - Original mating organisms
                     - Example:  True-breeding Purple Flower  * True-breeding White Flower

                b.  First Filial Generation = F₁ - First generation of offspring
                     - Hybrid - offspring from two different parents
                     - Example:  Purple Flowers

                c.  Second Filial Generation = F₂ - Second generation of offspring
                     - Example:  75% Purple and 25% White Flowers

     C.  Alleles
           1.  Definition - alternative forms or versions of a gene

           2.  Homozygous vs. Heterozygous - two conditions that exist depending upon both alleles present for a particular trait
                a.  Homozygous - two of the same allele for a trait found on homologous chromosomes (BB in diagram below)
                b.  Heterozygous - two different alleles for a trait found on homologous chromosomes (Aa in diagram below)
                                         

           3.  Dominant vs. Recessive - classification of alleles based on which allele for a trait is actually expressed
                a.  Dominant - allele that expresses itself; represented by a capital letter (Example = Purple Flower Pea Plant)
                b.  Recessive - allele that is present, but NOT expressed; represented by a lower case letter (Example = White Flower Pea Plant)

           4.  Genotype vs. Phenotype
                a.  Genotype - arrangement of alleles and genes present in organism
                b.  Phenotype - visual or chemical expression of these genes (Remember that genes alone do not determine phenotype.  The environment also plays a role.)
                c.  Example:
                                        Genotype              Phenotype
Homozygous Dominant            PP               Purple Flowers
Heterozygous Dominant            Pp               Purple Flowers
Homozygous Recessive            pp                White Flowers

     D.  Mendel's Genetic Laws
           1.  Law of Dominance - When organisms having pure contrasting traits are crossed, their offspring will show only one of the traits
                Example:  
                  (P₁)  Purple Flowers (PP) * White Flowers (pp)
                  (F₁) All Purple Flowers (Pp)

           2.  Law of Segregation - Each gamete receives only one of each parent's pair of genes for that trait (one allele from each parent)
                -  These gametes combine at random to form new gene pairs at fertilization.

To test your knowledge about Basic Genetic Principles, click on the Basic Questions Link at the top of this page.  After you answer the questions, be sure to check your responses by clicking on the Basic Answers Link.

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