2. Section 1: Mendel´s work
Gregor Mendel made
experiments on plants that
revolutionized the study of
heredity
Heredity is the passing of
physical characteristics from
parents to offspring
3. Each different form of a characteristic is
called a trait
Ex: eye color
Mendel observed plant traits such as
height and seed color
Genetics is the study of heredity
4. Mendel´s experiments
Mendel used pea plants
He developed a method by which he cross-
pollinated, or “crossed” pea plants: he took
pollen from one and brushed it into the
second plant
Fertilization is the process in which an egg
cell and a sperm cell join to form a new
organism
5.
6. Crossing pea plants
Mendel crossed plants with contrasting
traits (ex: tall and short)
He started with purebred plants
A purebred organism is the offspring of
many generations that have the same
trait
7. The F1 offspring
Mendel crossed purebred tall plants
with purebred short plants (P= parental
generation)
The offspring from this cross are called
F1 generation
All the F1 plants were tall
8. The F2 offspring
The F1 generation self-pollinated,
resulting in the F2 generation
Some plants were tall and some short
in the F2 generation
Tall= ¾ plants
Short= ¼ plants
9.
10. In all of Mendel´s crosses, only one
form of the trait appeared in the F1
generation. However, in the F2
generation, the “lost” form of the
trait always reappeared in about one
fourth of the plants
11. Dominant and recessive
alleles
A gene is the set of information that controls a
trait.
Alleles are the different forms of a gene
An orgnaism´s traits are controlled by the alleles
it inherits from its parents. Some alleles are
dominant, while other alleles are recessive.
12. A dominant allele is one whose trait
always shows up in the organism when
the allele is present. Ex: Y
A recessive allele is hidden whenever
the dominant allele is present. Ex: y
13.
14. A hybrid is an organism that has 2
different alleles for a trait
Ex: Yy
15. A dominant allele is represented by a
capital letter (Ex. T= tall)
A recessive allele is represented by a
lowercase letter (Ex. t= short)
Examples:
Purebred= TT, tt
Hybrid= Tt
16.
17. Mendel´s contribution
Mendel´s discoveries demonstrated that
traits are determined by individual,
separate alleles inherited from each
parent rather than being a blend from
the parents´traits
