6.3 Mendel and Heredity
KEY CONCEPT
Mendel’s research showed that traits are inherited as
discrete units called genes (made of DNA).
6.3 Mendel and Heredity
Mendel laid the groundwork for genetics.
• Traits are distinguishing
characteristics that are
inherited.
• Genetics is the study of
biological inheritance patterns
and variation.
• Gregor Mendel showed that
traits are inherited as discrete
units—was a monk who
worked with pea plants b/c are
easy to breed
• Many in Mendel’s day thought
traits were blended.
6.3 Mendel and Heredity
Mendel’s data revealed patterns of inheritance.
• Mendel made three key choices in his experiments.
– use of purebred plants
– control over breeding
– observation of seven
“either-or” traits that
appeared in two forms
(tall vs short, round vs
wrinkled)
6.3 Mendel and Heredity
Pea Plant characteristics:
•
•
•
•
•
•
•
Pea shape
Pea color
Flower color
Pod shape
Pod color
Flower position
Plant height
6.3 Mendel and Heredity
• Cross = mating of two organisms
• Mendel used pollen to fertilize selected pea plants.
– Plants can self-pollinate and be pure-bred or can be
cross-pollinated
– interrupted the self-pollination process by removing
male flower parts
– P (parental) generation crossed to produce F1 (first filial)
generation; F1 generation produces the F2 generation
Mendel controlled the
fertilization of his pea plants
by removing the male parts,
or stamens.
He then fertilized the female
part, or pistil, with pollen from
a different pea plant.
6.3 Mendel and Heredity
• P generation: Mendel cross-pollinated the plants used
purebred plants for the P generation (crossed pure white,
pure purple)
• F1 generation, resulted in all plants that had purple flowers
• Mendel allowed the resulting plants to self-pollinate
• F2 generation, resulted in some plants had purple flowers
and some had white
• What does this tell us??
6.3 Mendel and Heredity
• Results: for all 7 traits, Mendel found approximately ¾ of F2
offspring had one trait and ¼ had the other trait (3:1 ratio)
when examining ONE trait at a time
6.3 Mendel and Heredity
• Conclusions:
– Traits are inherited as discrete units we now call genes
•Law of Segregation
– Organisms inherit two copies of each gene, one from
each parent.
– The two copies segregate
(separate) during gamete
formation.
purple
white