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Introduction to Genetics
The Work of Gregor Mendel
Biology Text Chapter 11
The Beginning of Genetics
• Genetics is the study of heredity (Traits we inherit from our
parents).
• Gregor Mendel was an Austrian Monk who was in charge of
the monastery garden. Mendel carried out experiments with
garden peas.
• The original pea plants Mendel had were true-breeding.
True-breeding plants produce offspring identical to
themselves. Tall seeds produced tall plants, some produced
yellow seeds, etc.
Cross Pollination
• To cross pollinate pea plants, Mendel
cut off the male parts of one flower,
then using a brush dusted it was pollen
of another flower.
• In the example to the left, a purple
flower (Parent plant) was crossed with a
white flower pea plant (Parent plant).
• Purple flower color is dominate over the
white color. The first generation (F1)of
plant expresses its color as purple, but
also has recessive genes for white
flowers that might be expressed in its
offspring.
Genes and Dominance
• Mendel studied seven different
pea plant traits.
• Traits are specific
characteristics, like seed color
or plant height that varies from
one individual to another.
• Mendel crossed plants with the
seven different traits.
• Each original plant is a parent
(P) generation. The offspring
are called F1 or first filial. Filial
is Latin for son or daughter.
• Hybrids are the offspring of
parents with different traits.
Mendel’s Conclusions
• Mendel’s first conclusion was that traits are passed from one
generation to the next. From parents to offspring.
• Scientists call the chemicals that control and determine traits
genes.
• Different forms of a gene are called alleles. Alleles for plant
height are short or tall. Seed shape is a round allele or
wrinkled allele, etc.
Principle of Dominance
• Mendel’s second conclusion is the principle of dominance
• The principle of dominance states that some alleles are
dominant and others are recessive. When a dominant and
recessive allele are on a gene, the dominant allele will
express over the recessive gene.
• The capital letter represents the dominant allele and the
lowercase letter represents the recessive allele
Segregation
• Mendel wondered what happened to the
recessive alleles from the parent plant.
• He crossed two of the hybrid F1 plants to
produce the F2 or second filial
generation.
• The alleles separated during the
formation of gametes (sex cells) in the
F1.
• As the male and female gametes came
together, different dominant and
recessive plants were produced in the F2
generation.