A transgenic plant can be

1
A transgenic plant can be grown from a
transformed tissue culture cell. It will have a
transgene in every cell
2
A Hemizygous plant has only one copy of a
transgene.
Bt gene
One chromosome has the transgene
The other chromosome does not
3
When gametes are made, the paired chromosomes
separate. In a hemizygous plant, half of the
gametes will have a copy of the Bt gene, and half
will not.
Silk (egg)
Bt gene
Pollen
4
When two hemizygous plants are mated, the
gametes chromosomes will randomly pair.
Silk (egg)
Bt gene
Pollen
5
One in four offspring will have two copies of the
Bt gene.
Silk (egg)
Bt gene
Pollen
6
Two in four offspring will have one copy of the
Bt gene.
Silk (egg)
Bt gene
Pollen
7
One in four offspring will have no copies of the
Bt gene.
Silk (egg)
Bt gene
Pollen
8
A Homozygous plant has two copies of a transgene.
Bt gene
Bt gene

Both chromosomes have a copy of the transgene.
9
If a homozygous plant is mated with a hemizygous
plant, the possible genotypes of the offspring
would be different.
Silk (egg)
Bt gene
Pollen
10
Two of the four plants will have two copies of
the Bt gene.
Silk (egg)
Bt gene
Pollen
11
Two of the four off spring will have one copy of
the Bt gene.
Silk (egg)
Bt gene
Pollen
12
Lines that work well in genetic engineering
typically have poor agronomic traits.
Transgenic Elite
Inbred (GE) plant
13
Plant breeders use the backcross breeding method
to move the transgene into an elite line with
good agronomic traits.
Transgenic Elite
Inbred (GE) plant
14
The seed from this cross will be called the F1
generation seed. Half of its genes will be from
the transgenic donor parent, and half will be
from the elite inbred parent.
F1s
X
Transgenic Elite
Inbred (GE) plant
15
Backcross breeding begins by making a cross
between the transgenic inbred and the elite
inbred.
X
Transgenic Elite
Inbred (GE) plant
16
The F1 seed is planted. At the same time, more
seed from the elite recurrent parent is planted.
F1 seed Elite Inbred
next generation (next week in Hawaii)
17
The F1 plants are mated back to the elite inbred
parent.
BC1
X
F1 plant Elite Inbred
18
The seed from this cross is called the backcross
1 generation (BC1). It will have 75 elite
genes.
BC1 seed
X
F1 plant Elite
Inbred
( 50 elite genes 100 elite
genes ) / 2 parents 75 elite genes BC1
generation
19
Plants that have the Bt gene are selected from
the BC1 plants and crossed back to the elite
inbred.
BC2 seed
X
BC1 plant Elite
Inbred
( 75 elite genes 100
elite genes ) / 2 parents 87.5 elite
genes BC2 generation
20
Plants that have the Bt gene are selected from
BC2 plants and crossed back to the elite inbred.
BC3 seed
X
BC2 plant Elite
Inbred
( 87.5 elite genes 100
elite genes ) / 2 parents 93.75 elite
genes BC3 generation
21
This continues until plant breeders are
satisfied with the percentage of elite genes,
(usually 98-99). This may take 5-7 generations
of crossing.
BC4 seed
X
BC3 plant Elite
Inbred
( 93.75 elite genes 100
elite genes ) / 2 parents 96.875
elite genes BC4 generation
22
The BC corn lines must also be tested to screen
against any negative traits from either the
genetic engineering process or from the
agronomically poor parent.
23
X
Transgenic line
Elite Inbred (F1 seed)
F1 Plants have a consistent appearance.
F1 plants

The genetic makeup of the plants changes with
each generation of backcrossing.
24
X
Transgenic line
Elite Inbred (F1 seed)
Backcross 1 75 elite genes
X
F1 plants
Elite inbred (Backcross 1 seed)
Each generation, the backcross progeny will look
more like the elite parent.
25
Transgenic line
Elite
Backcross 1 seed 75 elite genes
Elite
F1 plants

BC1 plants are more variable in appearance
BC1
BC 1 plants are more variable because they may
receive different gene combinations from the F1
parents.
26
Transgenic line
Elite
Backcross 1 seed 75 elite
Elite
F1 plants
Backcross 2 seed 87.5 elite
BC1 Elite
Plants that are most similar to the elite parent
and have the Bt transgene are selected for
crossing back to the elite parent.
27
Transgenic line
Elite
Backcross 1 seed 75.0 elite
Elite
F1 plants
Backcross 2 seed 87.5 elite
BC1 plants Elite
BC 2 plants are beginning to look more like the
elite inbred parent.
BC2 plants
28
Transgenic line
Elite
The backcross progeny are becoming
genetically similar to the elite parent.
Elite
F1 plants
BC1 plants Elite
Backcross 3 seed 93.75 elite
BC2 plants Elite
29
Downside of Backcrossing -Takes time -
Conservative, no selection for yield increase
(yield lag)
1998
Bt gene backcrossed with
New 1998 Elite Hybrid 155 b/a
1995 Elite Hybrid 150 b/a
30
Bt
X
Bt hybrid Roundup Ready
Roundup Ready
Gene Stacking
31
Gene Stacking
Bt
X
Roundup Ready
Bt hybrid Roundup Ready
Bt Roundup
Bt
Roundup Ready
32
The Top Cross System
15 Oil
Breeder develops an elite male-sterile hybrid
33
The Top Cross System
X