Hh - HET AA - HOM ww - HOM Gg - HET Ff - HET SS - HOM

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 .

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
– 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: ____