Basic Genetics
The
Father
of
Genetics
Gregor Mendel
Gregor Mendel
Objectives:

To distinguish between
heredity and inheritance

To define pollination

To identify the major parts
of a flowering plant

To describe Mendel’s
experiments in heredity
Heredity – transmission of
traits from parents to their
offspring
Inheritance
passing of
traits by
heredity
Mendel’s experiments
used pea plants
Pollination – transfer of pollen from
anthers to stigma in flowers
1) self pollination
occurs within the
same flower or
same plant
2) cross pollination
occurs between
different plants
Receptical
Mendel’s Crosses with Pea Plants
P
parental
1 generation
Pure tall
plants
X
Cross
F1
F2
first filial
generation
Pollination
All Tall plants
Self
second filial
generation
Pure short
plants
Pollination
787 tall plants, 277 short plants
3 to 1 ratio
Objective:

To describe Mendel’s 3
principles of inheritance
1) Principle of Dominance and
Recessiveness

Each trait is controlled by 2
factors, one factor (dominant ) may
mask the other factor (recessive )
preventing it from having an effect.
P1
F1
F2
2) Principle of Segregation

The two
factors for a
characteristic
separate
during the
formation of
eggs and
sperm.
3) Principle of Independent
Assortment

Factors for
different
characteristics
are distributed
to reproductive
cells
independently.
Objectives:

To define gene

To define allele
Gene – segment of DNA on a
chromosome that codes for a
particular protein

genes
occur in
pairs
Allele – alternative form of a gene
T = tall
t = short
Recessive
Lowercase
letter
Dominant
capital
letter
G = green
pods
g = yellow
pods
Objectives:



To define genotype and
phenotype
To distinguish between
homozygous and
heterozygous
To define multiple alleles
Genotype – genetic makeup
of an organism (genes)
(internal information)
Phenotype –
physical
characteristics
of an organism
(external appearance)
What does Phenotypes come form
Example of Genotype and
Phenotype
TT
genotype
Tall
phenotype
Homozygous – when both alleles
of a pair are the
same
homozygous
dominant
homozygous
recessive
TT
tt
Heterozygous – when both alleles
of a pair are not
the same
heterozygous
(tall)
Tt
Multiple alleles – 3 or more alleles
that control a trait

Example – blood type (IA,IB,io)
GENOTYPES
IA IA
IAio
IB IB
IBio
IAIB
ioio
RESULTING PHENOTYPES
Type A
Type A
Type
Type
Type
Type
B
B
AB
O
Objectives:


To define probability
To predict the results
of monohybrid
crosses by using a
Punnett square
Probability – likelihood that a
particular event will occur
number of times a particular event occurs
Probability = number of opportunities for the event to occur
Example 1: Flipping a Coin
Chances of coming
up heads
=
½
Example 2: Rolling Dice
1
6
probability
of rolling a
six on 1 dice
x
1
6
probability
of rolling a
six on 1 dice
=
1
36
probability
of rolling a
six on 2 dice
monohybrid cross –
Objectives:



To define test cross
To define incomplete
dominance
To define codominance
Test cross – an individual with
unknown genotype is crossed
with a homozygous recessive
individual

used to determine
the genotype of
any individual
whose
phenotype is
dominant
In rabbits, black fur color is
dominant over brown fur color
B = black fur
b = brown fur
bb
BB or Bb
Incomplete Dominance

when 2 or more alleles
influence the phenotype
results in a trait

intermediate between
the dominant and
recessive traits
Incomplete Dominance
Codominance – condition in which
both alleles of a gene are expressed

example – roan coat in horses


white hair (HW) is codominant with red
hair (HR)
horses with genotype (HRHW) have
coats with a mixture of red and white
hairs (roan)
Roan Coat
Objectives:

To predict the results of
dihybrid crosses by using
a Punnett square
dihybrid cross – cross between
individuals that involves two pair of
contrasting traits