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GENETICS
Mendel’s expt.
Incomplete Dorminant
Codorminance
Multiple allele
Linkage and Sex Link
Crossover
Genetic Variation
Mendel
Some characteristics used in
mendel’s experiment
Monohybrid(Law of Sgregation)
SS Ss
Ss
ss
Exercise of Pedigree
Dihybrid
Law of Independent
Assortment
RrYy
x
RrYy
Backcross(self-pollination)
TT
x
T
TT
T
TT
T: tall pea
t: short pea
Tt
x
T
t
TT
Tt
Tt
T
Tt
t
tt
Test cross
To test animals with dominant
characteristics(LL or Ll)
LL
x
ll
L
L
l
Ll
Ll
Ll
Ll
l
Ll
x
ll
L
l
l
Ll
ll
Ll
l
ll
Incomplete Dominance
RR
rr
Rr
Codominance
Blood group
A
B
AB
O
Blood
cells
antigen
Multiple allele
Phenotype
A
B
AB
O
Ai
Bi
AB
ii
AA
BB
Genotype
Types of allele:
Dominant gene:
Recessive gene:
Person:
Blood Group:
Tonque roll :
1
2
3
4
Ai
Tt
i i
Tt
Bi
Tt
Ai
tt
Blood transfusion
White blood cell B
A
B
Antibody A
Red blood
cell with
antigen A
Linkage
Y: yellow flower, y: white flower, R: red fruit, r: yellow fruit
If: YyRr
x
YyRr
Ans: yellow flower red fruit : white flower yellow fruit
3
:
1
According to Law of independent assortment, the ratio
should be 9:3:3:1. Why?
Allele of flower color and allele of fruit color are on
the same chromosome.
F1 generation
Phenotype:
Yellow flower
Red fruit
Y
y
Y
y
R
r
R
r
Y
y
Y
y
R
r
R
r
Gamete
F2 generation
Y
Y
Y
y
Y
y
y
y
R
R
R
r
R
r
r
r
Genotype:
Ratio:
3
:
1
Sex Chromosome
SEX Linkage
Female Gamete
B
b
X X
B
X Y
x
Male Gamete
X
Y
B
X
B
X
b
XX
B
B
XX
B
b
XY
B
XY
b
Haemophilia
CROSS OVER
Source of Genetic Variation
Continuous and Discontinuous
Variation
Blood group
A
B
AB
O
Blood
cells
antigen
Polygenic Inheritance
Environmental Effect
Temperature
MUTATION
Chromosome
Mutation
Down’s Syndrome
Change in Sex Chromosome
number
Gene Mutation
Change of a gene sequence
AACCGTGGAC
AACCTTGGAC
Cause: Sickle Cell anaemia
Mutagen
Mutagen is any agents which cause mutation.
Chemical: colchicine inhibit spindle formation and
cause polyploidy, formaldehyde, nitrous acid and
mustard gas.
Radiation: high energy particles as  &  and also UV
light. UV can combine TT nucleotide in DNA chain and
so affect replication and transcription.