1. Prepared By:
Montalbo, Daniel Justin B.
De Castro, Ralph Louis R.

2.  Mendel’s Law of Segregation states that there are two alleles
for every gene determining a specific characteristic, and these
alleles are segregated into separate gametes during
reproduction.
 When the 2 different alleles occur together in one individual
(heterozygote), the dominant allele will be the one that is
expressed in the phenotype of the individual.
 The Law of Addition is used to combine probabilities, when
there are 2 or more ways to arrive at a given outcome.
 The Law of Multiplication is used to combine probabilities of 2
or more different events that need to occur in combination.
 Mendel’s Law of Independent Assortment says that 2 or
more different genes, if found on separate chromosomes, are
determined independently of each other.
 Many characteristics have been found to follow patterns of
inheritance that are modifications of Mendel’s rules.

3. • pure • forked line
• gene breeding • polygenes
• allele • hybrid • contributor
• dominant • homozygous y allele
• recessive • heterozygous • non-
contributor
• character • P (parental
y allele
generation)
• trait • continuous
• F1 (first filial variation
• phenotyp
generation) • discontinuo
e
• F2 (second us variation
• genotype
filial
generation)
• Punnett

4. CHARACTERS TRAITS
• Pre-Mendel beliefs in
genetics: blending
theory
• Augustinian monk and
science teacher
• Why Pisum sativum?
– Pea plants available in
many varieties
• character (heritable feature)
• trait (character variant)
– Perfect flowers
• cross-pollination and
self-pollination
– Short generation time
– Many offspring

5. MONOHYBRID CROSS
inheritance of a single trait
P Generation
(true-breeding
x
parents)
Purple White
flowers flowers
F1 Generation
(hybrids)
All plants had
purple flowers
self-pollination
F2 Generation
705 plants 224 plants

7. Allele for purple flowers
 Alternative versions
of genes exist
Homologous
(alleles)
Locus for flower-color gene pair of › Dominant
chromosomes
› Recessive
 Organism inherites
Allele for white flowers 2 alleles
› Dominant is fully
expressed
› Recessive has no
visible effect
 Law of segregation
› 2 alleles for one
character
separate and go
to different
gametes

8. True-breeding plants have identical P Generation
alleles. x
Purple flowers White flowers
Gametes each contain only one allele PP pp
for the flower-color gene. Every gamete Appearance:
produced by one parent has the same allele. Genetic makeup:
P p
Gametes:
F1 hybrids have a Pp combination.
Purple-flower allele is dominant, F1 Generation
all hybrids have purple flowers.
Purple flowers
Hybrid plants produce gametes, Appearance:
Genetic makeup: Pp
two alleles segregate: half the
gametes receiving the P allele and
1
/2 P
1
/2 p
Gametes:
the other half the p allele.
Punnett square: shows all possible F1 sperm
combinations of alleles in offspring P
p
from an F1 x F1 (Pp x Pp) cross. F2 Generation
P
Each square represents an equally probable PP Pp
product of fertilization. F1 eggs
p
Pp pp
Random combination of the gametes
results in the 3:1 ratio that Mendel
3 :1
observed in the F2 generation.

9. • Homozygous –
identical alleles,
true-breeding
• Heterozygous –
different alleles
• Phenotype –
physical
appearance
• Genotype –
genetic make-
up

10. APPLICATION
An organism displaying the dominant phenotype can either X
be homozygous or heterozygous for the trait. A test-cross will
help determine which.
Dominant phenotype, Recessive phenotype,
unknown genotype: known genotype:
TECHNIQUE PP or Pp? pp
The individual with the unknown genotype is crossed with
a homozygous individual expressing the recessive trait
(white flowers in this example). By observing the If Pp,
If PP,
phenotypes of the offspring resulting from this then 1⁄2 offspring purple
then all offspring
cross, we can deduce the genotype of the purple-flowered
purple: and 1⁄2 offspring white:
parent.
p p p p
RESULTS
P P
Pp Pp Pp Pp
P p
Pp Pp pp pp

11.  Illustrates the
inheritance of two
characters
 Produces four
phenotypes in the F2
generation
 Law of Addition -
combines probabilities
for mutually exclusive
events
 The Law of
Multiplication -
combines probabilities
of 2 or more
independent events
that need to occur
together

13. Forked Line Method
AaBbCc x AaBbCc

14. 1. Codominance
– two dominant alleles affect
phenotype in separate
ways
– both alleles manifest
– e.g. roan coloring in horses
– both red and white
2. Incomplete dominance
– phenotype of offspring is
between phenotypes of
two parents
– e.g. red and white parents
give rise to pink offspring
3. Multiple alleles
– genes with more than two
alleles that control the
phenotype
– e.g. ABO blood type system
has 3 alleles--A,B,i. A and B
are codominant, i is
recessive to both