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Manipulating genes. © Sir Ralph Riley. 2. Cross breeding. Ever since humans have been domesticating animals and raising crops they have been (unwittingly) manipulating genes. By cross pollination and cross breeding they have tried to introduce

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Slide1 l.jpg

Manipulatinggenes

© Sir Ralph Riley


Cross breeding l.jpg

2

Cross breeding

Ever since humans have been domesticating animals and raising crops

they have been (unwittingly) manipulating genes

By cross pollination and cross breeding they have tried to introduce

the beneficial characteristics of one variety into a different variety

of the same species*

For example, a bull born to a cow that has a good milk yield, might

be mated with a cow from a low-yielding stock, in the hope that the

offspring will inherit the characteristics which lead to a high milk yield

This has been done for thousands of years without any knowledge

of genes or the mechanism of inheritance


Crossing l.jpg

3

Crossing

In the following (hypothetical) example, a variety of high yielding

wheat which has poor resistance to disease…

…is crossed with a variety which has good disease resistance but

gives a poor yield

The gene* for ‘high yield’ is represented by H

The gene for ‘low yield’ is represented by h

The gene for ‘good disease resistance’ is represented by R

The gene for ‘poor disease resistance’ is represented by r


Slide4 l.jpg

4

pollen

grain

ovule

HHrr

high yield

low resistance

hhRR

low yield

high resistance

The F1 consists of

plants with high yield

and good resistance

zygote


Slide5 l.jpg

5

Can you see any disadvantages in this method of

manipulating genes ?

Try working out what would happen if you tried to breed from

the F1

Work out the various gene combinations in the gametes

Put them into a

4x4 Punnett Square


F 1 cross l.jpg
F1 cross

6

F1 cross HhRr x HhRr

Possible combination

of genes in gametes

HR

Hr

hR

hr

HR

Hr

hR

hr

HhRR

HhRr

HR

HHRR

HHRr

HHRr

Hr

HHrr

HhRr

Hhrr

hR

HhRR

HhRr

hhRR

hhRr

hr

Hhrr

hhRr

HhRr

hhrr

The F1 does not breed true. Of the 16 possible combinations

of genes, 7 do not have the combined beneficial genes


Wheat l.jpg

7

wheat

a

b

c

d

e

Manipulating genes

by cross breeding

Wheat variety (a)

was crossed with

wild grass (b) to give

hybrid wheat (c)

Hybrid wheat (c) was

crossed with wild

wild grass (d) to give

hybrid wheat (e) used

for making flour and

bread

a xb

= c

c x d

= e

© Sir Ralph Riley


Genetic engineering l.jpg

8

Genetic engineering

Interbreeding transfers the complete genome of one variety to

another.

This means that many new and unpredictable gene combinations

may be formed in addition to those intended

This method of genetic recombination can take place only between

varieties of the same or closely related species

Genetic engineering makes it possible to transfer single genes

The genes can also be transferred from one species to a totally

different species


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9

Plasmids

There are several ways in which genes from one organism can be

inserted into a different organism

They can be coated on to microscopic gold particles and ‘fired’

into the cells

They can be delivered by viruses

They can be transmitted by using structures, called plasmids,

present in bacteria

For example, the human gene for making insulin can be transferred

to bacteria, which are then allowed to reproduce in a culture medium

from which the insulin can be extracted


A bacterium l.jpg
A bacterium

10

in addition to a loop of DNA…

…bacteria also contain numerous

rings of DNA called plasmids

cell wall

cytoplasm

0.001mm

cell membrane

the plasmids can be

extracted and used for

genetic engineering


Inserting a gene l.jpg

11

Inserting a gene

plasmid

human DNA

strand

restriction

enzyme cuts

plasmid

the same

restriction

enzyme cuts

the insulin gene

out of the

human DNA

insulin

gene

the insulin gene

is inserted into

the plasmid


Recombinant plastids l.jpg
Recombinant plastids

12

The recombinant plastids are

inserted into a bacterium *

the insulin gene makes the

bacterium produce insulin


Applications l.jpg
Applications

13

Only about 1 in 100,000 bacteria take up the recombined plasmids

There are techniques for identifying and isolating these bacteria

The bacteria with the insulin gene are then allowed to reproduce

in a culture solution from which the insulin can be extracted*

Human growth hormone can be made in a similar way

Factor VIII, needed by haemophiliacs, (blood clotting disorders)

can be produced from hamster cells containing plasmids with the

factor VIII genes

Chymosin, used for clotting milk in cheese-making, can be

produced from yeast cells with recombinant plasmid DNA


Applications14 l.jpg
Applications

14

As well as producing useful substances from genetically altered cells, whole organisms can be genetically modified.

Some examples are ….

A bacterial gene which makes an insecticide can be introduced into

crop plants, e.g. maize and cotton, to make them resistant to attack

by moth caterpillars

A gene which confers resistance to herbicides has been inserted

into crop plants so that spraying kills weeds but not the crop plants

A gene introduced to oilseed rape makes the oil more suitable

for commercial processes, e.g. detergent production

Genes which control the production of human enzymes have been

inserted into sheep so that the enzymes can be recovered from

their milk


Applications15 l.jpg
Applications

15

Genetic engineering does not always have to involve gene transfer

between unrelated organisms

Genes in a single organism can be modified to improve their

characteristics or their products

A gene for the production of ß carotene (a precursor of Vitamin A)

has been introduced to rice to benefit countries where rice is the

staple diet and Vitamin A deficiencies are common*

The next slide shows tomatoes which have been genetically

modified to suppress production of an enzyme which causes the

fruit to soften as it ripens. This improves the keeping qualities


Tomatoes l.jpg
Tomatoes

Genetically modified

Control tomatoes

Genetically modified tomatoes

After storage

After storage

© AstraZeneca


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17

Opponents of genetic engineering stripped the bark off these poplars

in order to kill them.

A gene had been inserted which softened the cell walls so that fewer

environmentally damaging chemicals were needed in paper-making.


Cloning l.jpg
Cloning

18

When organisms reproduce asexually, all the offspring receive a full

set of genes from the parent.

As a result they are identical to each other and to the parent

Examples are

Bacteria and single-celled organisms

Plants with vegetative reproduction by bulbs, corms etc.

Fungi

Some of the lower invertebrates

A population of identical individuals arising from asexual

reproduction is called a clone


Clone of crocuses l.jpg

19

Clone of crocuses

A clone of crocuses


Bacterial clone l.jpg
Bacterial clone

Next slide


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20

Vertebrates do not reproduce asexually but clones can be produced

artificially

In some cases this is done by transferring the nucleus from a body

cell to an egg cell (ovum) from which the nucleus has been removed

The following slide illustrates one of the first successful

techniques for cloning a mammal


Dolly l.jpg

21

Dolly

cells in sheep A’s

mammary gland

egg cell (ovum)

from sheep B

diploid

nucleus

one cell

isolated

nucleus

removed

the two cells

are fused together *

cell division produces

early embryo

embryo implanted

in uterus of sheep C

cloned lamb

born


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22

Sheep, pigs, horses, cows and, by now, probably many more animals

have been cloned

So far, this is being done on an experimental basis

Hundreds of embryos have to be prepared and implanted to obtain

one or two successful births

If the process becomes cheap and reliable it means that beneficial

genes will be present in all the offspring, thus eliminating the

chances of their being lost during conventional breeding

Before the early embryo is implanted in the surrogate mother, it can

be broken up into its individual cells. Each of these can develop into

a new embryo


Slide24 l.jpg

23

fertilised frog egg

at the 8-cell stage, any one of these

cells can develop into a frog

cell division to form

an embryo

growth and development to

produce tadpole and frog


Clone of frogs l.jpg

24

Clone of frogs

each cell can develop into a frog

8-cell frog embryo

cells separated


Embryonic stem cells l.jpg

25

Embryonic stem cells

The cells from the 8-cell embryo are called embryonicstem cells….

…because each one can form all the cells and tissues to

produce a complete frog

After the 16-cell stage, the cells lose this ability and can only

produce specialised cells such as blood, bone and nerve cells

Cells capable of dividing to produce specialised cells are

called stem cells

Specialised cells normally lose the power to divide and may have

a limited life span

The tissues produced by specialised cells usually contain some

stem cells which retain the power of division


Skin stem cells l.jpg

26

Skin stem cells

hair

basal layer

cells worn away

epidermis

cells dividing

dermis

basal cells

(skin stem cells)

2mm

these stem cells keep

dividing and pushing

new skin cells to the

outside

fat layer

section through skin


Blood stem cells l.jpg
Blood stem cells

27

red cells

several types

of white cell

stem cell in red

bone marrow

produces ……..

platelets


Slide29 l.jpg

28

Skin stem cells can normally give rise only to skin epidermal cells

Bone marrow stem cells can normally give rise only to 6 types of blood cell

But embryonic stem cells can produce all the cells of the body

Human embryonic stem cells can be obtained from 10 day embryos*

These embryonic stem cells can be cultured in a special nutrient

solution


Human escs l.jpg

29

Human ESCs

section through a 10-day

human embryo

these cells will contribute

to the placenta

stem cells transferred

to culture dish

0.5 mm

nutrient medium*

stem cells cultured

(cloned)

these cells will form

the embryo (stem cells)


Slide31 l.jpg

30

All the cells in the body have a full set of genes

When the cells become specialised, they lose their ability to divide

and many of the genes are ‘switched off’

For example, the genes for producing hydrochloric acid in a stomach

cell would not be functional in a skin cell

Even though tissues consist mainly of specialised cells, most of them

also contain their own stem cells

It may become possible to treat stem cells from specialised tissues

with hormones and growth factors that cause them to produce a

wider range of specialised cells*


Applications of stem cells l.jpg
Applications of stem cells

31

Most applications of stem cells are in the experimental stage, are

undergoing clinical trials or have been tried on very few patients

Possibilities are

Replacement of damaged tissues such as heart muscle, skin,

bone and cartilage

Treatment of disease, e.g. diabetes by injecting islet cells

into the pancreas; or Parkinson’s disease by injecting nerve

stem cells into the brain

If the stem cells can be derived from the patient’s own tissue,

rejection by the immune system is avoided


Question 1 l.jpg
Question 1

What are the possible gene combinations in the gametes

From genotypesAAbbandaaBB?

(a) Ab

(b) AB

(c) ab

(d) aB


Question 2 l.jpg
Question 2

Which of the following statements is correct?

F1 hybrids from cross breeding or cross pollination…

(a) …may not be able to reproduce

(b) …can contain genes from unrelated species

(c) …may contain unwanted gene combinations

(d) …may not breed true


Question 3 l.jpg
Question 3

Genetic engineering can

(a) Transfer genes only within a species

(b) Transfer single genes between species

(c) Create new species

(d) Modify a species


Question 4 l.jpg
Question 4

The bacterial components which can be used to transfer

genes are

(a) mitochondria

(b) DNA

(c) plasmids

(d) proteins


Question 5 l.jpg
Question 5

DNA which has been genetically engineered is called…

(a) Engineered DNA

(b) Hybrid DNA

(c) Modified DNA

(d) Recombinant DNA


Question 6 l.jpg
Question 6

Which of the following can be made by genetically

engineered bacteria ?

  • Human insulin

(b) Human growth factor

(c) Blood-clotting Factor VIII

(d) Blood platelets


Question 7 l.jpg
Question 7

Which of the following could be described as a clone ?

  • A litter of kittens

(b) A clump of daffodils

(c) A bacterial culture

(d) An F1 hybrid


Question 8 l.jpg
Question 8

A cell is removed from cow P. An ovum is obtained from cow Q

and its nucleus is removed. The cell from P is fused with the

enucleated ovum from Q. The combined cell starts to form an

embryo which is transplanted into the uterus of Cow R and in due

course a calf is born.

Which of these cows is the biological parent of the calf?

  • P

(b) Q

(c) R

(d) The calf does not

have a biological parent


Question 9 l.jpg
Question 9

Which of these statements is correct ?

(a) All cells can produce new tissue

(b) Only stem cells can produce new tissue

(c) Stem cells can divide

(d) All cells can divide


Question 10 l.jpg
Question 10

Embryonic stem cells differ from other stem cells because …

  • They can produce only one type of tissue

(b) They can produce a complete organism

(c) They can produce all kinds of cell

(d) They cannot be cloned


Answer l.jpg
Answer

Correct


Answer44 l.jpg
Answer

Incorrect


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