GENETICS

Everyone receives one set of chromosomes from their mother and one set of chromosomes from their father, ie, half their genetic material comes from their mother and half comes from their father. This explains why you may look more like one or other of your parents.

46 chromosomes 46 chromosomes

meiosis

Egg cell with 23 chromosomes

meiosis

Sperm cell with 23 chromosomes

Fertilization

A child with 46 chromosomes with some

characteristics of his mother and some of his

father.

ALLELES

Paternal

chromosome

Maternal

chromosome

- For eye colour

Alleles – for hair colour

Alleles – for straight or

curly hair

Brown eyes

Homozygous blue

Blue eyes Brown eyes

Homozygous

brownHeterozygous

brown

M P M PM P

Brown eyes is dominant to blue eyes – the gene for brown eyes is

represented by ‘B’.

Blue eyes is recessive to brown eyes – the gene for blue eyes is

represented by ‘b’.

Homozygous blue Homozygous

brownHeterozygous

brown

M MMP PP

bb BbBB

HOW WAS ALL OF THIS DISCOVERED????

Pure breeding tall pea

plantX Pure breeding short pea

plant

All the offspring were tall

Tall offspring X Tall offspring

A ratio of 3 tall plants

to 1 short plant.

P1

meiosis

gametes

Tall x Short

TT tt

T T t t

phenotype

genotype

T T

t Tt Tt

t Tt Tt

F1 Genotype Tt

Phenotype All tall

P2

meiosis

gametes

Tall x Tall

Tt Tt

T t T t

phenotype

genotype

T t

T TT Tt

t Tt tt

F1 Genotype TT; 2Tt; tt

Phenotype 3 Tall : 1 Short

Phenotypic ratio 3 : 1

Mendel’s Findings• Mendel called the characteristic that showed in the F1, the

dominant characteristic.

• He called the characteristic that was hidden the

recessive characteristic

•For each characteristic, there are only two genes which

segregate so that each gamete has only one of these

genes. This is Mendel’s First Law: The Law of

Segregation.

•The various genes are separate entities and do not

influence each other in any way. They sort themselves

out independently during gamete formation. This is

Mendel’s Second Law: The Law of Independent

Assortment

Examples of dominant

characteristics

Hand Clasping

Clasp your hands together (without

thinking about it!). Most people place their

left thumb on top of their right and this

happens to be the dominant phenotype.

Now, for fun, try clasping your hands so

that the opposite thumb is on top. Feels

strange and unnatural, doesn’t it?

Alleles: L,l

Dominant phenotype: left thumb on top

Dominant genotype: L –

Recessive genotype: ll

Bent Little Finger

A dominant allele causes the

last joint of the little finger to

dramatically bend inward

toward the 4th finger. Lay

both hands flat on a table

relax your muscles, and note

whether your have a bent or

straight little finger.

Alleles: B, b

Dominant phenotype: bent

little finger

Dominant genotype: B –

Recessive genotype: bb

Tongue

Try to roll your tongue into a tube.

The ability to roll your tongue is the

dominant phenotype. If you cannot

roll your tongue it does not matter

how much you try you will never be

able to do it.

Alleles: T,t

Dominant phenotype: the ability to

roll your tongue

Dominant genotype: T –

Recessive genotype: tl

Monohybrid crosses with

DominanceThe gene for red flowers is dominant over white. A homozygous red flowering plant is

crossed with a homozygous white flowering plant to produce the F1 generation

1. Determine the genotype and phenotype of the F1 generation. Illustrate your

answer in the form of a diagram.

2. If the F1 generation were allowed to self-pollinate, determine the genotypic ration

and phenotypic ratio of the F2 generation.

3. If 200 seeds were produced in the F2 generation, how many would germinate into

plants with red flowers and how many will germinate into plants with white flowers?

Monohybrid Crosses with Dominance

P1 Red flowers x White flowers

RR rr

R R r r

meiosis

gametes

phenotype

genotype

R R

r Rr Rr

r Rr Rr

F1 Genotype Rr

Phenotype All red

P2

meiosis

gametes

Red x Red

Rr Rr

R r R r

phenotype

genotype

R r

R RR Rr

r Rr rr

F1 Genotype RR; 2Rr; rr

Phenotype 3 Red : 1 White

Phenotypic ratio 3 : 1

When a black rabbit is crossed with a white rabbit, all offspring produced are grey.

X

How does this happen?

Monohybrid Cross without

Dominance

(Incomplete Dominance)

Monohybrid Crosses without Dominance

P1 Black x White

BB WW

B B W W

meiosis

gametes

phenotype

genotype

B B

W BW BW

W BW BW

F1 Genotype BW

Phenotype All grey

P2 Grey x Grey

BW BW

B W B W

meiosis

gametes

phenotype

genotype

B W

B BB BW

W BW WW

F2 Genotype BB; 2BW; WW

Phenotype 1 black; 2 grey; 1 white

Family resemblance

What is variation?People are similar, but not identical, to their

parents and siblings. The differences within a

species are called variation.

People inherit characteristics from both parents

and each person gets a different combination of

features. This is called inherited variation.

Variation can come about for two reasons. What

are they?

Other characteristics are affected by a person’s surroundings. This

called environmental variation.

Dihybrid Crosses

A dihybrid cross involves two pairs of contrasting characteristics, e.g. round, yellow seed crossed with wrinkled green seeds.

X

X

Yellow is dominant

Round is dominant

Green is recessive

Wrinkled is recessive

YYRR X yyrr

YR yr

meiosis

gametes

P1 genotype

RY RY RY RY

ry RrYy RrYy RrYy RrYy

ry RrYy RrYy RrYy RrYy

ry RrYy RrYy RrYy RrYy

ry RrYy RrYy RrYy RrYy

F1 genotype RrYy

phenotype all round, yellow seeds

X

YyRr X YyRr

YR

meiosis

gametes

P2 phenotype

genotype

Yellow , round Yellow , round

yR Yr yr YR yR Yr yr

RY Ry rY ry

RY RRYY RRYy RrYY RrYy

Ry RRYy RRyy RrYy Rryy

rY RrYY RrYy rrYY rrYy

ry RrYy Rryy rrYy rryy

F1 genotype 1RRYY, 2RRYy,

2RrYY, 4RrYy, 2Rryy,

1RRyy, 1rrYY, 2rrYy,

1rryy

phenotype 9 round, yellow

3 round, green

3 wrinkled yellow

1 wrinkled green

SEX DETERMINATION IN HUMANS

XX XY

X X X Y

X Y

X XX XY

X XX XY

2XX and 2XY

50% chance of having a boy or a girl

GENE

MUTATIONS

During DNA replication, the base pairs maybe altered and

the new DNA formed is slightly different from the original.

This may be caused by X-rays, ultra-violet radiation and

certain chemical agents.

Most gene mutations are harmless but some may cause

problems such as sickle-cell anaemia and haemophilia.

Most people with Marfan Syndrome

are taller than normal. Males can

often reach at least 6’5” and most

females are taller than 6 feet.

Individuals with this disorder usually

have abnormally long arms and legs

that are out of proportion to the rest

of their body. They often have long,

thin fingers and toes and very

flexible joints.

Another characteristic of Marfan

Syndrome is a long, narrow face

and a small jaw. The roof of the

mouth may be high and crowded

teeth are common.

Many individuals have hunched

shoulders, a curved spine or

backbone and flat feet. Their

breastbone is often deformed and

either caves in or sticks out.

Stretch marks on the skin and

hernias are also very common and

almost every person with Marfan

Syndrome experiences eye

problems.

Marfan Syndrome

NATURAL SELECTION

Within a population the individuals show considerable

variation due to crossing over and the random

assortment of genes.

The individuals with the variation which makes them

best adapted to the environment will survive and

reproduce. Their offspring will carry the genes for the

favorable characteristics.

The individuals with variations that make them less

adapted to the environment either die or are unable

to reproduce. As they do not produce offspring the

unfavorable genes disappear from the gene pool

PRACTICAL APPLICATIONS

OF GENETICS

29/03/2020

Selective breeding

I raise cows. Each type of cow is good at a certain job. The Friesian cow produces large quantities of milk, the Jersey cow produces very nice milk

and the Hereford cow produces lot of beef.

If, for example, I want lots of milk I would only breed Friesian cows with each other – this is

SELECTIVE BREEDING.

Friesian

Jersey

Hereford

Selective breedingSelective breeding is a process used to produce different breeds of animals or

varieties of plants that have useful characteristics.

Farmers can choose individual cows to

mate in order to produce a generation of

cows that will yield more milk.

Apple growers want to produce a type of apple that is

tasty and resistant to disease.

This can be done by crossing a variety of apple known

for taste with another variety that shows strong

resistance to disease.

BLOOD GROUPS

BLOOD GROUP

(Phenotype)

GENES

(Genotype)

O ii

AB IAIB

A IAIA or IAi

B IBIB or IBi

Two parents, one heterozygous for A blood group and one heterozygous for B

blood group produce children. Determine the possible phenotypes and

genotypes of the children.

P1 A type blood x B type blood

IAi IBi

IA i IB i

meiosis

gametes

phenotype

genotype

IA i

IB IAIB IBi

i IAi ii

F1 Genotype IAIB; IAi; IBi; ii

Phenotype AB; A; B; O

A mother who is heterozygous for blood group A and a father with blood

group O have two children. The children have different blood groups. What

type of blood do they have?

P1 A type blood x O type blood

IAi ii

IA i i i

meiosis

gametes

phenotype

genotype

IA i

i IAi ii

i IAi ii

F1 Genotype IAi; ii

Phenotype A; O

Mrs Steyn and Mrs Stassen both had babies in the same hospital on 24 May

2007. Mrs Steyn’s baby was born at 03:44am and Mrs Stassen’s baby at

0:45am. The tags with the babies’ names were put around their wrists

straight after birth to identify them. Jana was given to Mrs Steyn and Laura

to Mrs Stassen. However, after 3 days the mothers instinctively felt that the

babies had been switched at birth. They insisted on blood tests to determine

whether this had indeed happened. The results of the blood tests were as

follows.

Mr Steyn - A

Mrs Steyn - B

Mr Stassen - A

Mrs Stassen - AB

Jana - A

Laura - O

Use genetic diagrams to determine whether or not a switch took place.

P1 A type blood x B type blood

IAi IBi

IA i IB i

meiosis

gametes

phenotype

genotype

IA i

IB IAIB IBi

i IAi ii

F1 Genotype IAIB; IAi; IBi; ii

Phenotype A; B; AB; O

The Steyns

Mrs Steyn must be IAi and Mr Steyn must be IBi

The Stassens

Mrs Stassen can be AA or AO and Mr Stassen is AB.

Either cross can produce a child with A type blood but Mr and Mrs

Stassen can never have a child with O type blood.

ANSWER

Yes, a swop did take place. The Steyns are the only couple

that are able to have a child with O type blood. This means

that Laura belongs to the Steyn’s and Jana belongs to the

Stassens.

RHESUS FACTOR

RHESUS DISEASE

PRENATAL

DIAGNOSTIC

TESTING

Percutaneous

umbilical

blood sample

Each abnormality can be classified into one of three levels

LEVEL 1

The mutation causes part of a single gene to be altered.

Colour blindness, Sickle cell anaemia, Haemophilia, Albinism,

Cystic fibrosis, Severe combined immunodeficiency

LEVEL 2

An entire chromosome or large portion of it is missing (deletion), doubled

(duplicated), turned around (inverted) or altered in some way where part of

a chromosome may break off and join a non-homologous chromosome.

Klinefelter syndrome, Down’s syndrome, Cri-du-Chat syndrome, Turner

syndrome, Williams syndrome, Huntington’s disease

LEVEL 3

Mutations occur in multiple genes and is often linked to environmental

causes

Alzheimer’s disease, Colon cancer, Breast cancer, Ovarian cancer,

Hypothyroidism

Cystic Fibrosis Severe Combined

Immunodeficiency

CF is a chronic, progressive and genetic (inherited) disease of the body's exocrine (mucus producing) glands CF primarily affects the respiratory, digestive and reproductive systems, as well as the sweat glands. The mucus secreted is very thick and blocks passageways in the lungs and digestive tracts.

SCID is actually a group of inherited disorders that cause severe abnormalities of the immune system. These disorders lead to reduced or malfunctioning T- and B-lymphocytes, the specialized white blood cells made in the bone marrow to fight infection. When the immune system doesn't function properly, it can be difficult or impossible for it to battle viruses, bacteria, and fungi that cause infections.

Cri-du-Chat syndrome

Cri du chat syndrome (French for cry or call of the cat), is a rare genetic disorder due to a missing part of chromosome 5. The condition affects an estimated 1 in 20,000 to 50,000 live births. The syndrome gets its name from the characteristic of the cry of infants born with the disorder. The infant sounds just like a meowing kitten, due to problems with the larynx and nervous system. Other symptoms of cri du chat syndrome may include:

•feeding problems because of difficulty swallowing and sucking, •low birth weight and poor growth, •severe cognitive, speech, and motor delays, •behavioral problems such as hyperactivity, aggression, tantrums, and repetitive movements, •unusual facial features which may change over time. •excessive dribbling. •constipation.

Huntington’s diseaseWilliams syndrome

A rare neurodevelopmental disordercaused by a deletion of about 26 genes from the long arm of chromosome 7. It is characterized by a distinctive, "elfin" facial appearance, along with a low nasal bridge; an unusually cheerful demeanor and ease with strangers; mental retardation coupled with unusual (for persons who are diagnosed as mentally retarded) language skills; a love for music; and cardiovascular problems .

The most characteristic physical symptoms are jerky,

random, and uncontrollable movements called

chorea. In a few cases, very slow movement and

stiffness (called bradykinesia and dystonia) occur

instead. As the disease progresses, any function that

requires muscle control is affected, causing physical

instability, abnormal facial expression, and difficulties

chewing and swallowing. Eating difficulties

commonly cause weight loss and may lead to

malnutrition.

Select cognitive abilities are impaired progressively.

Psychiatric symptoms vary far more than cognitive

and physical ones, and may include anxiety,

depression, a reduced display of emotions (blunted

affect), egocentrism, aggression, and compulsive

behavior, which can cause, or worsen addictions,

including alcoholism and gambling.

Hypothyroidism

Hypothyroidism is the disease state in humans and in animals caused by insufficient production of thyroid hormone by the thyroid gland. Cretinismis a form of hypothyroidism found in infants.

Primary hypothyroidism occurs when the thyroid gland does not produce enough thyroxin.

Secondary hypothyroidism occurs when the bodies cells are unable to use the thyroxin even though there is enough present.

The reduced ability of people to distinguish between certain colours. It is

a sex-linked inherited disease that affects mostly men.

There are three types of cone cells in the retina. If one or more types of

cone cells becomes faulty then the person becomes colour blind.

inability to see

the color red or

to distinguish

red and bluish-

green (the most

common kind)

inability to see

the color blue

or to

distinguish the

colors blue

and yellow

inability to see

the color green

or to

distinguish

green and

purplish-red

TYPE OF COLOUR BLINDNESS

Colour blindness can show up as :

1. Different shades of red appear dull and indistinct.

2. Shades of green orange, red and brown all appear as the same hue

and may be distinguished only by their intensity.

In one type all

colours

cannot be

distinguished

and vision is

only black and

white.

In another

very rare type,

yellows and

blues cannot

be

distinguished.

P1Normal female (carrier) x Normal male

XBXb XBY

XBXb

XB Y

meiosis

gametes

phenotype

genotype

XB Xb

XB XBXB XBXb

Y XBY XbY

F1 Genotype XBXB; XBXb; XBY; XbY

Phenotype 2 normal females,

1 normal male, 1 colour blind male

There is no particular treatment if it is inherited. If it is caused by

medication then the medication must be stopped immediately. If

there are underlying eye disorders then those must be treated.

SCA is caused by a mutation in a gene on chromosome 11 which causes the abnormal formation of haemoglobin molecules. This results in RBC’s becoming rigid and having a concave shape like a sickle. These cells cannot transport oxygen efficiently, and they tend to get stuck in blood vessels

Symptoms

1. Damage to organs like heart, liver, lungs, kidneys, spleen due to a lack of oxygen.

2. Low RBC count (anaemia)

3. Episodes of pain called ‘crisis’ due to RBC’s becoming stuck in the blood vessels

4. Strokes

5. Delayed growth

6. Jaundice

Diagnosis

Most newborns are screened for the disease with a simple blood test. If not detected at birth a test called haemoglobin electrophoresis is performed.

Treatment

Babies and children are usually given a daily dose of penicillin to prevent infections. Patients are advised to take folic acid to help build RBC’s, to get plenty of rest, avoid strenuous activity and to drink plenty of water. Blood transfusions can be performed and in the most severe cases patients may be treated with a bone marrow transplant

Symptoms

Blood does not clot well. Internal bleeding, especially at the joints occurs.

Diagnosis

Parents can undergo genetic testing to determine if they are carriers.

Treatment

Haemophiliacs are normally given injections of purified clotting agents that have

been extracted from human blood plasma. Dangers involved include HIV and

rejection. Patients were therefore given drugs to suppress the immune system.

These days, however, most of the clotting factors are harvested from genetically

engineered organisms and therefore produce few side-effects.

P1Normal female (carrier) x Normal male

XHXh XHY

XHXh

XH Y

meiosis

gametes

phenotype

genotype

XH Xh

XH XHXH XHXh

Y XHY XhY

F1 Genotype XHXH; XHXh; XHY; XhY

Phenotype 2 normal females,

1 normal male, 1 haemophiliac male

Albinism is characterized by the inability of the patient to produce melanin of the skin, hair and eyes. There are about 10 different kinds of albinism. The most common is oculocutaneous albinism which affects the eyes, skin and hair. It is caused by a mutation on chromosome 15. The type of albinism that affects only the eyes is called ocular albinism. It is caused by a mutation on the X chromosome.

Symptoms

1. The eyes are usually light brown to pale in colour, sensitive to the sun and may display nystagmus (fast, involuntary back and forth movements) or strabismus (squinting). Vision could also be impaired.

2. The skin is very light in colour and is sensitive to sunlight. Freckles or pigmentation patches could develop.

3. Hair ranges in colour from reddish, light brown, yellow to white with eyebrows and eyelashes also being yellow to whitish.

4. Intelligence is within the normal range although infants may seem a little slower in developing because of their visual problems.

Diagnosis

DNA testing and parents can undergo screening before having children.

Treatment

There is no cure. People with the disorder have to learn to manage it. Many people with the disorder are stigmatised by their communities. Greater effort is required to educate the public about this disorder.

Myths

1. It is caused by the food that the mother ate

2. The mother may have laughed at a person with albinism.

3. The mother had a fright or an accident during pregnancy

4. If the mother is a person of colour then she had a sexual encounter with a white person

5. People with albinism have supernatural powers.

6. People with albinism do not die, they disappear.

A genetic disorder that only affects males. They have an extra X chromosome which gives them a total of 47 chromosomes. It is caused by nondisjunction, i.e. a pair of chromosomes fail to separate during meiosis either during the formation of the egg or the sperm.

Symptoms

1. The extra X chromosome mainly affects the testes. This affects the production of testosterone and sperm. At puberty the males normally grow tall and display subtle male characteristics. They usually, however do not develop male secondary sex characteristics.

2. Males develop more breast tissue than normal and have a less muscular body.

Many males have no idea they have the syndrome until puberty or until they try to have children and they are usually sterile as they cannot produce sperm.

Diagnosis

As an adult DNA testing is done. Prenatal testing can also be performed to screen for the abnormality before birth.

Treatment

Hormone replacement therapy which involves testosterone injections.

Phenotype female x male

Genotype XX XY

meiosis

XXX Y

nondisjunction

XXX

Female

Usually self-aborts

XXY

Male with Klinefelter

syndrome

Phenotype female x male

Genotype XX XY

meiosis

XXY

nondisjunction

XXY

Male with Klinefelter

syndrome

GENERAL INFORMATION

Down’s Syndrome is caused by an extra copy of chromosome 21. It is the most common genetic disorder caused by a chromosomal abnormality and it affects as many as 1 out of every 800 babies. It is caused by nondisjunction during the development of the sperm or the egg where a pair of chromosome 21 fail to separate during meiosis.

(Trisomy 21)

General cont…

In very rare cases it is caused by translocation which occurs when one of the arms of chromosome 21 breaks off and then becomes attached to the centromere of another chromosome. This will lead to the person being a carrier of Down’s but will not display the symptoms.

Symptoms

•A flat face

•Upwardly slanting eyes

•A small broad nose

•Abnormally shaped ears

•A large tongue

Increased risk of developing respiratory infections, heart defects, hearing loss, gastrointestinal tract obstructions, leukaemia, eye abnormalities, hypothyroidism and moderate to severe retardation.

Diagnosis

•Ultrasound

•Alpha-Fetoprotein Plus test and the Triple Screen Test

•Amniocentesis, chorionic villus sampling or precutaneous umbilical cord sampling.

•At birth due to the distinctive features.

Treatment

There is no cure and treatment is supportive and palliative.

GENERAL INFORMATION

This disorder can affect as many as 1 in 2000

babies. It is caused by either a missing X

chromosome or an incomplete X chromosome

and people with this syndrome develop as

females.

It is also caused by nondisjunction where a pair

of sex chromosomes fails to separate during

meiosis.

XX

XXXX -- --

FEMALE

X

+

This child will have 45 chromosomes and

cannot survive

-Y

X

X-

This child will have 45 chromosomes and can

survive

+

General cont…

The syndrome is not an inherited disorder, since women with this disorder are usually sterile.

Symptoms

It affects both growth and sexual development. One of the missing genes on the X

chromosome is responsible for long bone growth so girls who have this disorder are short.

Other missing genes regulate ovarian development and so the ovaries, eggs and sex

hormones cannot develop properly. Girls may be:

1. Short and stocky.

2. They may not start puberty when they should.

3. Have a short webbed neck.

4. Have a receding lower jaw.

5. Their arms may turn out slightly at the elbows

6. Have a low hairline at the back of the neck.

Other symptoms may include lymphedema, heart and kidney defects, high blood pressure and

infertility.

Diagnosis

Diagnosis is made using physical symptoms after the baby is born. Many patients are only

diagnosed in adolescence when they fail to go through puberty. Diagnosis can be

confirmed with a blood sample. Diagnosis can be done before birth but only if the doctor

suspects a problem.

Treatment

Hormone replacement therapy and growth hormone. Low doses of androgens are also given to

promote growth in height and to encourage the normal development of muscles and hair.

20 year old girl who I believe has Turner

syndrome (next to an American medical student who volunteered to help with our mission)

Alzheimer’s causes dementia and affects

those parts of the brain that deal with memory,

thought and language.

The most common form is linked to a gene

known as the apoE gene on chromosome 19.

This form of the disease occurs after the age

of 65

Rarer forms of this disease strike much earlier

in life and are caused by mutations on

chromosome 1, 14 and 21. Scientists don’t

know how this disorder develops but it may be

caused by a combination of genes and

environmental factors.

The forms of Alzheimer’s that strike early in life

are inherited in an autosomal dominant

pattern. This means that the presence of a

single defective gene results in the individual

developing Alzheirmer’s

Symptoms

Patients slowly lose their ability to think clearly. At first they forget names, where they put their

belongings or they may even start to forget words. As the disorder worsens they may forget

how to do simple things like combing their hair. Some patients also feel sad and/or nervous

Treatment

There is no cure for Alzheimer’s. Doctors prescribe medication to treat the symptoms. Patients

often need a caregiver to help them around and to do the things that they are unable to.

Descent Into Alzheimer’s

29/03/2020

Cloning1) Cloning plants:

2) Cloning sheep:

Cloning, however, is not new. Many organisms in

nature reproduce themselves, i.e. asexual

reproduction.

Farmers have also used it for thousands of years to

clone plants, i.e. vegetative reproduction.

During their experimenting with growing different

plants, farmers devised breeding techniques to

reproduce plants that would yield larger fruit or seeds

etc. This was the beginning of selective breeding.

29/03/2020

Selective breeding

I raise cows. Each type of cow is good at a certain job. The Friesian cow produces large quantities of milk, the Jersey cow produces very nice milk

and the Hereford cow produces lot of beef.

If, for example, I want lots of milk I would only breed Friesian cows with each other – this is

SELECTIVE BREEDING.

Friesian

Jersey

Hereford

Eventually scientists combined selective breeding techniques with cloning to produce many plants with desired traits. This later led to genetic engineering in which they manipulate DNA to create a plant with the exact desired traits very quickly and very accurately, e.g. GM foods

Advantages of GM Foods

1. Pest resistant

2. Herbicide tolerant

3. Disease resistance

4. Cold tolerant

5. Drought tolerant/salinity tolerant

6. Enhanced nutrition

7. Production of pharmaceuticals

Other Uses of Genetic Engineering

Controversies

1. ManyGenetically engineered plants to clean up heavy metal pollution from the environment.

2. Producing bacteria to consume pollutants.

3. Genetic modification of animals to give them new characteristics. They can then be used to produce commercial products, eg insulin for diabetics or clotting agent for hemophiliacs

4. people are opposed to the cloning of animals despite scientists arguing that this could lead to great advancements in medicine, the saving of endangered species or the resurrection of extinct species.

5. The fear that transgenic organisms could develop new diseases that could cause widespread epidemics.

6. Premature aging in cloned animals.

Stem Cell Cloning

When an embryo reaches the blastocyst stage the embryo contains cells that can differentiate into any type of cell, i.e. embryonic stem cells.

These stem cells can become any cell in the body but they lose this ability as they age. Adult stem cells from bone marrow seem to be the only stem cells that retain this ability.

SOURCE OF STEM CELLS

• Blood from the umbilical cord of a newborn.

• From embryos in a laboratory.

Pedigrees and Genetic Counselling

A pedigree is a diagram that represents the interrelationships of a family across the generations. A genetic counselor will draw up a pedigree to illustrate how a genetic disorder is inherited within a family. They will then use this pedigree to counsell a coupe about having children.