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 self-
pollinate
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 .
6.
7. Mendel’s First Experiments
Mendel crossed
purple flowers with
white flowers. The
offspring from this
cross is called first-
generation 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 first-
generation 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
– homozygousorganism
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: ____