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1. MENDELLIAN PRINCIPLES
OF HEREDITY
Christine Joyce Javier ☺
II – LOVE
January 18, 2012

2. Millions of different kinds of organisms
abound our Earth and they reproduces only its
own kind. It didn’t ever happen that a cat can
produce puppies as well as dogs can’t produce
kittens. Cabbage seeds will not ever produce
pepper. For a long time no one understood how
traits were inherited, until an Austrian monk
tinkered in his garden and observe his peas.

3. MENDEL’S GARDEN PEAS EXPERIMENT
Gregor Mendel, as a
monk, also spent this time
in the garden. He studied
the different structural
characteristics and growing
habits of plants. Finally,
he selected the garden
peas for his experiments. What do you think are
the reasons why he used the peas for his study?

4. REASONS FOR CHOOSING GARDEN PEAS
1.) Garden peas have presence of observable
traits with contrasting forms.
2.) Garden peas reproduce at a fast rate and
reproduce several generations in a short time.
3.) They are hardy plants. They do not need
much caring.
4.) Garden peas have its own structural
adaptation of self-pollination.

5. PROCEDURE OF THE EXPERIMENT
Mendel used 29, 000 pea plants and
obtained 14 varieties of seeds. He chose to
study the 7 traits. Each trait had two or more
forms, like height in the pea plant is a trait
with two-forms: short and tall. Pea plants do
not grow to be middle-sized.

6. RESULTS OF THE EXPERIMENT
Traits – is the general characteristics of the peas
(or any other organism). For example, the color
of the seed.
Characters – is the specific characteristics of the
peas (or any other organism). For example,
yellow or green seed.

7. RESULTS OF THE EXPERIMENT

8. RESULTS OF THE EXPERIMENT
After the research with plants, the basic
underlying principles of heredity that he
discovered also apply to people and other
animals because the mechanisms of heredity
are essentially the same for all complex life
forms.
In our book, we have there “3 Principles of
Heredity” but in other references, they just only
have 2.

9. DEFINITION OF TERMS
 Genes – section of a chromosome; control
what traits any living thing will have and
controls what traits a living thing can pass to
its young.
 Dominant Trait – trait that hides another trait.
 Recessive Trait – trait that is hidden.
 Purebreeding or Truebreeding – when the
traits of the offsprings are the same as the
parent plant for several generations.
 P Generation – parent generation.

10. DEFINITION OF TERMS
 Allele - is one of two or more forms of a gene;
groups of genes.
 F1 Generation – first filial generation, or the
offsprings of P generation.
 F2 Generation – second filial generation, or the
offsprings of F1 generation.
 Genotype – genetic makeup of the cell.
 Phenotype – organism's observable
characteristics or traits; external appearance
of an individual.

11. DEFINITION OF TERMS
 Homozygous – has 2 of the identical (same)
alleles of a gene.
 Heterozygous – has 2 different alleles of a
gene.
 Punnett Square – is a diagram that is used to
predict an outcome of a particular cross or
breeding experiment.
 Heredity – passing of traits to offspring.

12. BASIC PRINCIPLES OF HEREDITY
Some biologists refer to Mendel‘s
“principles“ as "laws".
1.) The Law of Dominance
2.) The Law of Segregation
3.) The Law of Independent Assortment

13. 1ST LAW: THE LAW OF DOMINANCE
It states that: “when purbreeding plants
having contrasting characters are crossed, all
the offsprings will show only one of the
characters. The character that appears is
dominant and the one that does not is
recessive.”
Meaning: When certain genes, come in 2 forms,
one trait will be expressed over the other
(dominant form over the recessive one).

14. 1ST LAW: THE LAW OF DOMINANCE
Ex: In the P Generation, there was a purple
flower and a white flower. They were
combined. Don’t expect that the result of the
flower color was light violet. For the F1
Generation, all plants have purple flowers. The
purple form of the trait was visible but the
white form was hidden. For the F2 Generation,
the ¾ of plants have purple flowers, and ¼ only
of them have white flowers.

15. 1ST LAW: THE LAW OF DOMINANCE
Dominant Form
(visible):Purple form
Recessive Form
(hidden):White form

16. 2ND LAW: THE LAW OF SEGREGATION
It states that: “two genes of a pair separate
or segregate during gamete formation.
Therefore, the traits are distributed.”
Meaning: Members of a pair of genes for
hereditary characters separate cleanly from
each other so that only one members of the
pair of genes goes into a particular gamete.

17. 2ND LAW: THE LAW OF SEGREGATION
Ex: During the formation of gametes, mother or
father’s alleles segregate (separate) so that
each zygote (fertilized egg) only carries
a single complete copy of a gene. In the
picture on the next slide, T=Tall and t=short. In
the F2 generation, each zygote either has one
"T" or one "t" from mother or one "T" or one
"t" from father.

18. 2ND LAW: THE LAW OF SEGREGATION
They segregated from
the dominate factor and
expressed in its original
state.

19. 3RD LAW: THE LAW OF INDEPENDENT ASSORTMENT
It states that: “the expression of one
particular trait does not affect the expression
of another trait.”
Meaning: A trait of one gene does not affect
the inheritance of another trait. The genes are
inherited independently.

20. 3RD LAW: THE LAW OF INDEPENDENT ASSORTMENT
Ex: The F2 Generation
produced 4 types: round
yellow, round green,
wrinkled yellow, and
wrinkled green. The result
was the dominant trait of
(round shape) did not affect
the recessive trait of another
kind (green color). Therefore, the green color
(recessive) can appear in both round and wrinkled.
The seed color trait does not affect the shape of
the seed.

21. PUNNETT SQUARE
It is a diagram that is used to predict an
outcome of a particular cross or breeding
experiment.
Example: