14-19 Learning Core Development Programme

Laura BlacoeConnah’s Quay High School

Aim

To help pupils understand more about the importance of the increasing

knowledge of genetics and how and why people inherit genetic disorders.

Lesson Objectives

We are learning:

That genetic information is found in the nucleus of every cell in the body and determines characteristics.

That genetic information is inherited from parents and that in each pair of chromosomes one is inherited from the mother and one from the father.

That diseases and disorders can be inherited.

Lesson Outcomes

What I am looking for:

TYC describe what DNA, genes and chromosomes are and how they determine characteristics.

TYC describe how genetic information is inherited and use genetic cross diagrams to determine the possible genotype of offspring.

TYC describe the symptoms of 4 different genetic diseases and explain how they are inherited. Also, predict possible genotype of offspring using genetic cross diagrams.

Sexual Fertilisation

Zygote

Embryo

Foetus

Human Chromosomes

Using letters to represent alleles

Dominant alleles = Capital letterRecessive alleles = Lower case letter

of the dominant allele

Black hair allele = BRed hair allele = b

Genetic Crosses

B

b

B B

BB BB

Bb Bb

Black Hair Black Hair

Black Hair Black Hair

B

b

b

B

BB Bb

bb Bb

Mum’s Genotype

Dad

’s

Genoty

pe

Activity 1 – Huntington’s Disease

Huntington’s disease is a fatal disease that affects the nervous system. It is caused by a defective allele on chromosome 4. It affects both men and women and makes the body shake uncontrollably.

Faulty allele = HNormal allele = h

Answers to activity 1

H

h

h h

Hh

hh hh

Hh

Extension Activity

John and Karen have both discovered that they have the genetic disorder Huntington’s disease.

But, they already have 2 children together. Explain to them (using genetic cross diagrams) the possibilities of their children’s genotype.

Answers to extension activity

H

H

H H

HH HH

HH HH

H

h

H H

HH

HhHh

HH

HhHH

H h

H

h hhHh

Activity 2 – Cystic Fibrosis

Cystic Fibrosis is a genetic disorder caused by a recessive faulty allele. C = Normal allelec = Faulty alleleCystic Fibrosis affects the cells membranes and causes the production of excess mucus in the respiratory organs and digestive system.

C

c

C

c

Cc

Cc Cc

Cc

Activity 3 – Sickle Cell Anaemia

Distribution of Sickle Cell sufferers

S

s

S s

SS Ss

Ss ss

Activity 4 - HaemophiliaSymptoms: Main symptom is that

blood does not clot properly.

Even small cuts and tooth extractions can be lethal due to blood loss.

Small knocks can cause internal bleeding and big bruises and joints may also bleed.

Treatment

The condition can be treated quite successfully by regular injections of the clotting factor – FACTOR 8.

Haemophilia – The sex-linked Gene

• Sex linked means only present in males or females.

• Haemophilia is only present in males.

• Sex-linked conditions occur when the there’s a defective allelle on the X-chromosome.

• Any recessive genes on the man’s X-chromosome will express themselves because their equivalent gene is missing form the shorter Y-chromosome.

There are 5 possible combinations for the blood clotting allele

Normal Male XHY

Haemophiliac Male

XhY

Normal Female

XHXH

Carrier Female

XHXh

Zygote does not develop

XhXh

You can’t have a male carrier without them having the disease.

There are no female sufferers because the offspring don’t develop.

H = Normal

h = Haemophiliac

XHY XHXh

XH Y XH Xh

XHXh

XHXH XHY XhY

Parent Genotypes

Normal Female

Carrier Female

Normal Male

Haemophiliac Male

Genetic Cross Diagram for Haemophilia