Transcript IA and IB are codominant with each other

Genetics
 Genetics- is the branch of biology which
studies heredity and variation among
related organisms. It is the science of
heredity
 Heredity-the transmission of
characteristics from parents to offspring
INHERITABLE CHARACTERISTICS
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Eye color
Height
Bone structure
Hair color
Skin color
Foot Size
MENDEL AND PEAS
 Gregor Mendel: the 1st
person to predict how
traits are passed on
 Austrian (Movarian)
Monk (1822-84)
 Interested in
mathematics and
botany and combined
the two to make a
statistical study of peas
for a period of eight
years (1857-65)
WHY MENDEL CHOSE PEAS:
1. Showed some definite characteristics
 Height: tall and short
 Flower color: white and various colors
 Seed color: yellow and green
 Seed shape: round and wrinkle
2. Peas usually self-pollinate:
a. Flower is the reproductive
structure in seed plants.
1. Each flower contains stamens
which produce pollen grains which
form sperm nuclei
2. Each flower contains a pistil which
contains egg cells at its base.
3. The transfer of pollen from
stamens to pistil results in
fertilization
4. This called pollination
b. Self-Pollination
1. Mechanism: Pollen is
transferred from
stamens to pistil on the
same flower or on
flowers of the same
plant
2. Purpose: selfpollinating plants
generally breed true
generation after
generation
c. Cross-pollination
1. Mechanism:
Pollen is transferred
from one plant to the
flowers of a different
plant
2. Purpose: Since
egg and sperm come
from different plants
you can study how
contrasting traits are
passed on in heredity
DETERMINATION OF A PURE
CHARACTERISTIC
 Mendel planted seeds of self-pollinated
plants to see if they would show the same
characteristics as their parent plant.
 If generation after generation, the
characteristic appeared, he called this a
pure characteristic.
EXAMPLES
 Seeds from tall
plants always
produced tall
plants
 Yellow seeds
always produce
plants that develop
yellow seeds
THE LAW OF DOMINANCE
 Mendel then cross-pollinated a short plant with a
tall plant
 He found that one characteristic dominated or
masked the other
 This trait he called the dominant trait
 The hidden trait was called the recessive trait
Tall x Short  all tall plants (dominant trait)
 The law of dominance states that in two
contrasting characteristics (tall vs. short;
wrinkled seeds vs. round seeds) that one
characteristic will dominate the other
Dominant and Recessive Traits
THE F NUMBER
 The first generation produced by a cross is
called the F1 or first filial (sons &
daughters) generation
 The second generation after a cross is the
F2 (F1 x F1) etc.
 The parents are designated as P generation
THE LAW OF UNIT CHARACTERS
 1st generation: Mendel made a Cross of a
tall and short pea plant; offspring were all
tall
 2nd generation: crossed 2 plants from the
previous generation; offspring were 75%
tall and 25% short
Law of unit characters Cont.
 From this observation and w/o knowing
about chromosomes and genes or DNA,
Mendel developed the Law of Unit
Characters:
 States: that inherited characteristics are
controlled by factors (called genes) that
occur in pairs
How to determine if you are dominant
or recessive for a trait
 Probability: likelihood that a particular trait
will exist.
 Punnett squares: square that shows all
possible combinations of alleles that may
result.
 Male alleles go on top of square, female
alleles on left side of square.
Homozygous or Heterozygous
How do you determine if you use 2 capital
letters,
2 lowercase letters or 1 capital and 1 lowercase
letter?
 Homozygous: 2 identical alleles for a trait.
Ex. Mom is homozygous dominant tall-TT
Dad is homozygous recessive short-tt.
 Heterozygous: 2 different alleles for a trait.
Ex. Mom is heterozygous tall-Tt
 Each parent will be either homozygous or
heterozygous for each trait.
 Phenotype: visible trait (what you
see)
 Genotype: genetic make-up (letters)
(height)
Ex: Mom is TT.
What is her phenotype?
What is her genotype?
Ex. Dad is Tt.
What is his phenotype?
What is his genotype?
Ex. Daughter is tt.
What is her phenotype?
What is her genotype?
Both parents are
DOMINANT
T
for
 T TALL
T
T
TT
TT
TT
TT
T
T
Both Parents are
Heterozygous
1 TT, 2Tt, 1tt so there is a 1:2:1 ratio genotypically
and a 3:1 ration phenotypically
Both parents are
RECESSIVE
Short.
t
t
t
tt
tt
t
tt
tt
Codominance: both alleles
expressed.
Incomplete dominance: neither allele is dominant or
recessive (blended) neither allele is dominant or
recessive (blended)
 Multiple Alleles:
* when there are more than 2 alleles for a
gene
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* in human blood types there 3 possible
alleles for the ABO blood typing system
IA = A antigen
IB = B antigen
i = no antigen
" both IA and IB are dominant over i but,
" both IA and IB are codominant with each
other (that means, they are both expressed
equally)
Blood Typing