Gregor Mendel conducted experiments with pea plants in the 1860s to understand the patterns of inheritance for different traits from one generation to the next. Through his experiments, he discovered that traits are passed from parents to offspring through discrete units that are now called genes. Mendel determined that for many traits, one gene variant is dominant and will be expressed over another recessive variant, but the recessive variant can still be passed down and expressed in later generations. Mendel's discoveries established the foundations of classical genetics and heredity through his laws of inheritance.

2. History of Genetics

During the 1860’s, an
Austrian monk and
teacher named
Gregor Mendel
experimented with
pea plants to see if
he could find a pattern
in the way certain
traits are handed
down from one
generation to the next
generation.

3. 
The passing of genetic traits from parents
to offspring is called heredity .

From working with plants, Mendel knew that
sometimes a trait in one generation
(parents) would not appear in the next
generation (offspring ). Then the trait
would show up in the next generation.

4. 

Pea plants were
a good choice to
study for these
reasons:
(1) grow quickly

(2) many different
kinds available

(3) able to selfpollinate

5. A self-pollinating plant has both
male and female reproductive
structures
 In cross-pollination, pollen from
one plant fertilizes the ovule of a
flower on a different plant.


Mendel only studied one characteristic
at a time, such as flower color .

7. Mendel’s First Experiments

Mendel crossed
purple flowers with
white flowers. The
offspring from this
cross is called firstgeneration plants
(F1). All were purple
—Where did the
white flower trait
go???

8. 

Dominant trait= the
trait observed in
the first generation
when parents that
have different traits
are bred
Recessive trait= a
trait that reappears
in a second
generation after
disappearing in the
first generation
when parents with
different traits are
bred

9. 

Mendel’s Second
Experiments
Mendel allowed firstgeneration plants to
self-pollinate . The
recessive trait for
white flowers
reappeared in the
second generation.

10. Gone, but Not Forgotten


Mendel realized that his results proved
that each plant has two sets of
instructions for each trait . Each
parent would then donate one set of
instructions.
Mendel’s work wasn’t widely
recognized until after his death, more
than 30 years later.

11. A Great Idea




Mendel knew from his experiments that there
must be two sets of instructions for each
characteristic scientists now call these
instructions for an inherited traits “genes”
Each parent gives one set of genes to the
offspring —the different forms of a gene are
known as alleles , like hair color
Dominant alleles are shown with a capital letter
Recessive alleles are shown with a lowercase
letter

12. Phenotype & Genotype

Organism’s
appearance is
known as its
phenotype
– Examples: hair
color, eye color,
widow’s peak,
etc.

13. 
Both inherited alleles
together form an
organism’s genotype
– homozygousorganism
with two dominant or
two recessive alleles,
like RR or rr for flower
color
– Heterozygous
organism that has one
dominant and one
recessive allele, like Rr
for flower color

14. Label each genotype as “HOM” for
homozygous or “HET” for heterozygous

Hh: ____
AA: ____

ww: ____
Gg: ____

Ff: _____
SS: ____