21/03/2016
Understanding Organisms
(OCR Gateway)
W Richards
The Weald School
B1a – Fitness and Health
21/03/2016
Modern diets and health problems
21/03/2016
% obesity in the UK
The Circulatory system
21/03/2016
The circulatory system is responsible
for pumping ______ around the body.
We need blood to be taken around the
body because blood contains ________
and _______. These are needed so
that all the ____ in our bodies can
produce _____ through _________.
Words – energy, blood, glucose,
respiration, oxygen, cells
Arteries and veins
21/03/2016
Arteries carry high pressure blood away from the heart to the
rest of the body. The blood is under pressure due to heart
contractions.
Veins carry low pressure blood back to the
heart. They have thinner, less elastic walls and
have valves to prevent backflow of blood.
Heart disease
Cholesterol
21/03/2016
21/03/2016
Heart disease and High Blood Pressure
Heart disease and high blood pressure are conditions where
the ______ and blood vessels experience extra strain. They
can be caused by:
• Excess weight
• High stress levels
• _____
• Excess _______
• Diets that are high in saturated ___, sugar or salt
Long term high blood pressure can cause blood vessels to
weaken or even ______. To DECREASE blood pressure
regular exercise and a balanced ____ are a good start!
Words – alcohol, burst, smoking, heart, fat, diet
Measuring Blood Pressure
21/03/2016
Blood pressure
measurements are
taken in terms of
“Systolic pressure
over diastolic
pressure”.
High blood pressure can cause
heart attacks, strokes, dementia,
heart disease and kidney disease.
Low blood pressure can cause
dizziness or fainting.
Fitness and Health
“Having good health” means
“being free from disease”
“Being fit” means “having an
good ability to do physical
activity” and can be measured in
terms of stamina, strength,
agility etc
21/03/2016
Smoking
21/03/2016
Cigarettes contain 3 harmful things:
1. NICOTINE, which is an ___________ drug that raises the
heart beat, narrows the arteries and so causes ____
_____ _____. This leads to heart _________.
2. TAR, which coats the lining of the _______ making them
less able to take in oxygen. It also contains carcinogens
which cause ______________.
3. CARBON MONOXIDE, which is a _______ ____ which
joins up with ____ blood cells making them incapable of
transporting _____________ around the body. In
pregnant women it can cause oxygen deprivation, leading to
low birth ______.
Words – high blood pressure, oxygen, red, addictive,
disease, poisonous gas, lungs, cancer, mass
Saturated Fat and Heart Disease
21/03/2016
B1b – Human Health and Diet
21/03/2016
Balanced diet
21/03/2016
A balanced diet should contain fats, proteins and
carbohydrates in roughly these amounts:
Carbohydrates
Fat
Protein
• Carbohydrates are simple sugars such as glucose
• Fats are made up of fatty acids and glycerol
• Proteins are made up of amino acids
A good balanced diet should also contain water, vitamins,
minerals and fibre.
Factors affecting choice of diet
21/03/2016
Personal choice,
e.g. vegetarianism
Age – teenagers
need more
protein
What factors affect
our choice of diet?
Activity – a
sporty lifestyle
will need more
energy
Religion – some
foods may be
banned
Allergies
Protein
21/03/2016
Proteins are long chains of amino acids.
There are two classes of protein:
• Essential amino acids (must be eaten)
• Non-essential amino acids (can be made in the
body)
Meat and fish are
“first class” proteins
People who do not eat enough protein will not grow
properly. Protein deficiency can result in a disease
called kwashiorkor, where the muscles waste away and
the belly swells. This is common in developing
countries where overpopulation and limited investment
in agriculture can cause food shortages. Proteins are
used by the body as an energy source if fats are not
present.
How much protein should we eat?
EAR of protein (in g) = 0.6 x body mass (in kg)
Storing Food in our bodies
21/03/2016
How do our bodies store food?
The liver converts glucose
and other carbohydrates
into insoluble glycogen to
be stored in the liver
Fats are stored under the
skin and around organs as
“adipose tissue”
Proteins are not stored in the body.
Body-Mass Index
21/03/2016
A commonly-used way to indicate is someone is overweight or
underweight is the Body Mass Index (BMI):
BMI =
Mass (kg)
Height2 (m2)
BMI
Meaning
<18.5
Underweight
18.5-25
Ideal
25-30
Overweight
30-40
Obese – obesity is linked to
heart disease, diabetes and
breast cancer
Eating disorders
21/03/2016
Anorexia nervosa – this is a condition where
sufferers restrict what they eat and
sometimes starve themselves, leading to
possible weight loss, abdominal pains,
discoloured skin, irregular periods etc.
Bulimia nervosa – this is when people vomit or
take laxatives straight after eating to get the
food out as quickly as possible. It can lead to
weight fluctuations, poor skin, hair loss,
irregular periods, tiredness etc.
B1c – Staying Healthy
21/03/2016
Pathogens
21/03/2016
Pathogens are microbes (micro organisms) that can cause
diseases. They can enter the body in a number of ways:
They can be
breathed in
through the
mouth or nose
…or other
natural
openings…
They can enter
through cuts or
bites in the skin
Spreading of Pathogens
21/03/2016
Diseases and pathogens can be spread by a number of means,
including:
Salmonella
Cholera
bacteria,
bacteria,
found in food
spread in
water
Influenza virus,
spread through
the air
Malaria, spread
through
“vectors”, e.g.
mosquitoes
Athlete’s foot, a
fungus spread
through contact
HIV, spread
through body
fluids
Microbes: our defence against them
21/03/2016
Our bodies have defence mechanisms against microbes:
The breathing
organs have hairs
and produce mucus
to cover the lining
of these organs and
The skin acts as
trap the microbes
a waterproof
barrier
If our skin is
cut platelets
seal the wound
by clotting
Our stomach contains
hydrochloric acid
However, these mechanisms can’t do anything about noninfectious diseases (e.g. cancer) or inherited diseases
(e.g. cystic fibrosis)
What pathogens do to us
21/03/2016
Pathogens can cause the
damage or death of cells,
e.g. in liver cirrhosis:
They can also damage the
body by producing toxins:
White blood cells
If microbes enter our body they need to be
neutralised or killed. This is done by
WHITE BLOOD CELLS:
White blood cells do 3 things:
1) They eat the microbe (these
white blood cells are called
“phagocytes”)
2) They produce antibodies to
neutralise the microbe
(“lymphocytes”)
3) The produce antitoxins to
neutralise the poisons produced
by microbes (lymphocytes again)
21/03/2016
Producing antibodies
21/03/2016
You’re going
down
Step 1: The lymphocyte “sees” the
pathogen (microbe)
Step 2: The cell produces
antibodies to “fit” the antigen
Step 3: The antibodies fit onto the
antigens and cause them to “clump”
Step 4: The pathogens are
“eaten” by the white blood cells
Specific antibodies
21/03/2016
Antibodies are specific for different antigens – they will
only neutralise the microbe they have been made for.
Fighting disease
NATURAL IMMUNITY
This is when antibodies are produced by a
person when needed or they are passed on by
the mother during pregnancy.
ARTIFICIAL IMMUNITY
Can be done in two ways:
1) A vaccine with dead microbes (which still carry
the antigen) is injected – the body is “tricked”
into producing antibodies ready for the real
thing. This is called PASSIVE
IMMUNISATION and the body then
“remembers” the microbe by producing memory
cells that “remember” it
2) The antibodies are injected directly into the
body – this is called ACTIVE IMMUNISATION.
21/03/2016
Vaccinations and Medicines
21/03/2016
Vaccinations have
eradicated some
diseases entirely
but they can
carry some side
effects.
Health problems can also be treated using antibiotics or
antivirals:
• Antibiotics are used to treat bacterial infections but they
have to be used sparingly or the bacteria might become
resistant (e.g. MRSA)
• Antivirals are used to treat a virus, such as HIV.
21/03/2016
The importance of testing drugs – e.g. Thalidomide
Mat Fraser,
comedian and actor
Tony Melendez,
guitarist
Developing new drugs
21/03/2016
Before a new drug can be approved it has to go through a
strict testing process. Consider the example of thalidomide:
Date
Event
Mid 1950s
Animal testing using thalidomide was undertaken.
Tests showed that it was safe but the tests were
“inadequate” – no tests were done on pregnant animals
Late 1950s
Thalidomide prescribed to pregnant mothers to help
sleep and morning sickness problems
Early 1960s
Babies are born with birth defects and the drug was
banned worldwide. Around 12,000 deformed
Thalidomide babies born, 4,000 die in first year.
Mid 1960s
Tests show that Thalidomide can help leprosy
sufferers and it is still used today for this purpose.
Researching new medicines
21/03/2016
Before new drugs can be approved they have to go through
three stages. What are the advantages and disadvantages of
each stage?
1. Is it toxic? Tests are done on cells
2. Is it safe for animals? Animal tests are
carried out
3. Is it safe for humans? Human
volunteers are tested on.
Placebos
21/03/2016
Clinical trials can be done in different ways:
1) Blind trials
Patients do not know which drugs they are taking – a real drug
or a “placebo”
2) Double blind trial
Neither the doctors or the patients know if they are taking
the real drug
Placebos offer anethical dilemma as a patient might be
sick and still be given a “dummy” pill. Also, you might
notice if you had a placebo as you wouldn’t get the side
effects of normal drugs...
Malaria
21/03/2016
Parasite
Host
The spread of malaria can be
restricted by:
• Sleeping under mosquito nets
• Taking malaria pills
• Avoiding being bitten
Cancer
21/03/2016
Cancer is a disease where cells show uncontrolled growth.
Our diets can affect our chances of getting cancer:
“Good” foods:
“Bad” foods:
Fruit
Salt
Vegetables
Saturated fats
Fibre
Red meat
Exercise can play a key part as well – Cancer Research UK
recommends “30 minutes a day of moderate activity” 5 days a
week, such as gardening, walking etc.
Tumours
21/03/2016
Tumours can be classed as “malignant” or “benign”:
Malignant tumours are cancerous and will still grow
Benign tumours are not cancerous – they may still
grow but won’t spread
This graph shows the
survival rates of different
types of cancer (source:
Cancer Research UK).
What conclusions can you
draw from it?
B1d – The Nervous System
21/03/2016
The Eye
Iris
Lens
21/03/2016
Sclera
Retina
Pupil
Optic
nerve
Cornea
Ciliary muscles
Blind
spot
Vision
“Binocular vision”
21/03/2016
“Monocular vision”
What are the advantages and disadvantages of each?
Seeing things
Rays of light are refracted
(bent) first by the cornea
and then by the lens. They
focus on the retina.
21/03/2016
Focussing on different distances
For distant objects the
ciliary muscles relax
and the suspensory
ligaments pull tight
making the lens pull
thin – the light doesn’t
bend as much.
For close objects the
ciliary muscles contract
allowing the lens to go
fat, thus bending the
light more.
21/03/2016
Problems with vision
Short sighted
Colour blindness,
caused by a lack
of specialised
cells in the cornea
Long sighted
21/03/2016
Using lenses to correct vision
21/03/2016
Short
Long
Laser eye surgery could also be used, which basically reshapes the cornea
The Nervous System
21/03/2016
The CENTRAL NERVOUS SYSTEM (CNS) enables us to react
to our surroundings. It consists mainly of the brain, the spinal
chord, nerve cells (“neurones”) and receptors.
Types of receptor:
1) Light receptors in the eyes
2) Sound receptors in the ears
3) Taste receptors on the tongue
4) Smell receptors in the nose
5) Touch, pressure and temperature receptors in the skin
6) Changes of position receptors in the ears (balance)
Nervous Reactions
21/03/2016
When we react to a stimulus our bodies use the following
pattern:
Stimulus
Receptor
For example, consider a
man and a camel:
Coordinator
Effector
Response
Oh
No!
What are the stimulus, receptor, coordinator, effector and
response in this situation?
Examples of reactions
Stimulus
Bright light
Sour taste
Losing balance
Sit on a drawing
pin
Receptor
(i.e. the thing
that detects the
stimulus)
Effector
(i.e. the thing
that will do the
reaction)
21/03/2016
Response
(i.e. action
taken)
Structure of a nerve cell
21/03/2016
Nucleus
Muscle strands
(effector)
Cell body
Axon
Myelin sheath – increases
the speed of transmission
Dendrons – conduct the
impulse to the cell
1) Motor neurone
2) Sensory neurone
Impulse
Impulse
3) Relay neurone
Synapses
21/03/2016
Neurones never ____ each other – there is a small gap
between them called a _____. A signal is sent from one
_______ to the next by a _______ transmitter across
the synapse. These transmitters are then ________.
Words – chemical, synapse, neurone, touch, destroyed
Conscious actions
21/03/2016
A conscious action is one where the brain makes a considered response.
Here’s what happens:
4) The brain
3) Here another sensory neurone
decides to move
carries the signal to the brain
away the hand
5) This impulse is
sent by MOTOR
NEURONES to the
hand muscles (the
effectors) via the
spinal chord…
2) The impulse is carried
by SENSORY NEURONES
to the spinal chord
1) Receptors in
your skin detect
a stimulus
Stimulus
6) Which then
moves the hand
away
Receptor
Motor Neurone
Sensory Neurone
Effector
Coordinator
Response
Reflex actions
21/03/2016
Sometimes conscious action is too slow to prevent harm, e.g…
In situations like this
the body bypasses the
brain to produce a
quicker response.
Here’s how it works…
Reflex actions
21/03/2016
3. Relay
neurone in the
spinal chord
2. Sensory
neurone
4. Motor
neurone
1. Receptor
5. Effector
Stimulus
Receptor
Motor Neurone
Sensory Neurone
Effector
Response
CNS
B1e – Drugs and You
21/03/2016
Cannabis: Pros and cons
21/03/2016
In January 2004 cannabis was changed from a class B drug to
a class C drug. Some people think that Cannabis should be
made legal. What are the pros and cons of cannabis?
Pros:
Cons:
Drugs Research Project
21/03/2016
Explain and give examples for the following:
1) Define the terms addiction, tolerance, withdrawal symptom and
rehabilitation.
2) Why do people use legal drugs?
3) What are the drawbacks of legal drugs?
4) Alchohol is a legal drug. What does it do to the human body?
5) Why do people use illegal drugs?
6) What are the drawbacks of illegal drugs? What can they cause?
7) Choose one drug and discuss how it affects the human body
Legal drugs
Drug
Effect on
activities
21/03/2016
Abnormal behaviour
caused
Caffeine/ other
stimulants
Reactions could
become faster
Highly strung, leads
to exhaustion
Alcohol
May make you
drowsy, you
shouldn’t drive
Leads to depressant
effects on the
nervous system
Paracetamol/
other painkillers
May make you
drowsy, you
shouldn’t drive
Side effects include
dizziness or itchiness
Overall, the effect of these legal drugs can be greater than the effect of
illegal drugs simply because more people use them.
Drugs
21/03/2016
Drugs are classed as “a substance that affects the central
nervous system, causing changes in psychological behaviour and
possibly addiction”. Some examples:
Type of drug
Effects
Examples
Painkiller
Block nervous
impulses
Morphine, aspirin,
paracetamol
Hallucinogen
Distort sense
perception
LSD
Stimulant
Increase reactions
Caffeine, nicotine,
ecstasy
Depressant
Slow down brain
activity
Alcohol, solvents,
termazapam
Synapses and drugs
21/03/2016
Depressant drugs can bind with ______ molecules in the
membrane of adjacent _______ and block the
transmission of an ______.
Stimulants can cause more ___________ to cross the
________.
Words – neurotransmitter, receptor, synapse, neurones, impulse
Investigating Reaction Times
21/03/2016
Task: Design an experiment that investigates the affect of
caffeine on reaction times.
Variables: What are the independent, dependant and control
variables?
Results: Draw your own results table:
Conclusion: What do your results show you?
Steroids
21/03/2016
Steroids are drugs that are used to boost athletic
performance. They’re banned and using them will lead to
disqualification from competing.
Ben Johnson, who ran the 100m in 9.79
seconds in 1988 but had his Olympic gold
medal stripped away from him after
testing positive for steroids.
This picture isn’t real…
Smoking revisited
21/03/2016
Cigarettes contain 4 harmful things:
1.
NICOTINE, which is an ___________ drug that raises the heart
beat, narrows the arteries and so causes ____ _____ _____. This
leads to heart _________.
2. TAR, which coats the lining of the _______ making them less able to
take in oxygen. It also contains carcinogens which cause
______________.
3. CARBON MONOXIDE, which is a _______ ____ which joins up with
____ blood cells making them incapable of transporting
_____________ around the body. In pregnant women it can cause
oxygen deprivation, leading to low birth ______.
4. Particulates, which accumulate in the lungs.
Words – high blood pressure, oxygen, red, addictive,
disease, poisonous gas, lungs, cancer, mass
Diffusion in the lungs
21/03/2016
Oxygen diffuses in and carbon dioxide diffuses out of blood in
the lungs:
CO2
Damaging the lings (emphysema)
21/03/2016
Another way smoking can
damage the body is
through destroying the
shape of alveoli:
Before
smoking
After
smoking – less
surface area
21/03/2016
More damage by smoking – smoker’s cough
The “pink” hairs in this photo
show cilia, small hairs lining
the windpipe that clear dust
and other particles away from
the air we breathe. Regular
smoking causes the cilia to
become paralysed and excess
mucous and tar build up in the
lungs, causing smoker’s cough.
Tobacco and Lung Cancer
21/03/2016
Smoking has existed in Western
culture since the 16th Century.
However, scientists only proved the
link between it and various diseases
shortly after the Second World War.
Over 50 years I proved the link between
smoking and lung cancer. I published my first
findings in 1950, based on patients in London
hospitals, and then studied 40,000 doctors and
proved a link in a paper published in 1954.
Sir Richard
Doll, 1912-2005
Cancer Research UK statistics
21/03/2016
What do these statistics imply?
The Effects of Alcohol
21/03/2016
Time
Effects
Short term
Blurred vision, lowering of inhibitions,
slowing of reactions (hence why there is a
limit on drink-driving)
Long term
Liver cirrhosis, brain damage
Alcohol content is measured in %ABV.
Wine is typically 12% while beer is 46%. 40% of hospital A&E incidents are
alcohol-related. When the liver
removes alcohol it turns it into toxic
chemicals that cause liver damage or
liver cirrhosis:
B1f – Staying in Balance
21/03/2016
Homeostasis
21/03/2016
Homeostasis means “controlling internal conditions”:
Waste products that need to be removed + how
CO2
Produced by respiration, removed via lungs
Internal conditions that need controlling + how
Temperature
Increased by shivering, lost by sweating
Water content
Increased and decreased by hormones
Some of these mechanisms are controlled by “negative
feedback” systems, i.e. the absence of a particular hormone
causes the reaction to change.
Measuring Body Temperature
21/03/2016
Some possible methods…
Body thermometers/
probes
Heat sensitive strips
Thermal imaging
Common places to measure temperature are in the armpit, the
mouth, the fingers, the ears or the anus.
Controlling Body Temperature
21/03/2016
Wow it’s hot! My body
temperature needs to stay at 37OC
as its the best temperature for
the enzymes in my body. How does
my body keep the temperature
right?
The thermoregulatory centre in the
brain detects “warm blood”.
Also, temperature sensors in the skin
detect the heat and send information
to the brain.
When the brain detects the high
temperature it takes two main steps....
Maintaining Body Temperature
21/03/2016
Cold
Hot
Vasodilation
Vasoconstriction
Vasodilation increases heat transfer to the surroundings and
heat is also lost through the evaporation of sweat.
Heat stroke and hypothermia
21/03/2016
21/03/2016
Body Temperature and the Nervous System
Nerve endings in the skin detect the
external temperature
Temperature detectors in the brain
detect the blood temperature
The hypothalamus coordinates a
response using hormones
Effectors (muscles and sweat glands)
carry out the response
Controlling Blood Sugar levels
21/03/2016
We need glucose in our bodies to help our cells to respire and
produce energy. What happens if we have too much glucose?
If blood sugar is too high the
pancreas releases insulin, which
travels in the blood stream. Insulin
lowers blood glucose levels by
converting glucose into insoluble
glycogen.
If glucose levels fall too low
then the hormone glucagon is
released from the pancreas
which causes liver to turn
glycogen back into glucose.
The trouble with hormones is
that they are slower than
nervous reactions.
Diabetes
21/03/2016
What is diabetes?
What do the pens (above right) do?
What does an insulin injection (above left) do?
What is the difference between Type 1 and Type 2 Diabetes?
How does physical activity affect Type 1 and Type 2
Diabetics?
Diabetes
21/03/2016
Type 1 Diabetes is a ________ in which a person’s blood sugar
(i.e. glucose) level may rise to a _______ level. This is
because the ______ doesn’t produce enough _________.
Physical activity will _______ the amount of glucose needed
by the body.
Diabetes can be treated by __________ carefully or by
injecting extra insulin when needed. Diabetics have to test
their blood sugar level before they decide how much insulin to
_______ themselves with. Type 2 Diabetes occurs when the
patient becomes _______ to insulin so the patient will have to
be careful regarding physical activity.
Words – insulin, disease, inject, dangerous, eating, pancreas,
increase, resistant
B1g – Controlling Plant Growth
21/03/2016
Plant Growth Introduction
21/03/2016
Plants grow due to their cells dividing through mitosis. The
cells then specialise into root hair cells, palisade cells etc.
Unlike animals, plants continue to grow for the rest of their
lives.
Plant Hormones
21/03/2016
The growth of roots and shoots is controlled by hormones
called auxins that move through the plant in solution:
In the shoots the hormone
auxin is “destroyed” by
light, so the shoot will bend
towards the light as the
cells on the shaded side
grow quickest.
In the roots hormones slow
down growth of the cells in
the lower region, which
makes the root bend down.
Some Definitions
21/03/2016
Shoots grow towards light (positive phototropism) and against
gravity (negative geotropism). This is caused by cell elongation
on the underside of the shoot and this happens because auxin
is made in the tip and is unevenly distributed through the
shoot.
Roots grow away from light (negative phototropism) and in the
direction of gravity (positive geotropism). This is caused by
cell elongation on the upper side of the root.
Artificial Plant Hormones
21/03/2016
Hormones can be used to help plant growth and the
development of fruit:
1) Auxin
2) Ethene
This hormone helps
fruit to develop
This hormone helps
fruit to ripen
Other uses include rooting powders (to help root
development), control of dormancy and weedkilling.
B1h – Variation and Inheritance
21/03/2016
Variation
21/03/2016
“Variation” is the name given to differences between
individuals of the SAME species.
Variation is due to GENETIC or ENVIRONMENTAL causes.
For example, consider dogs:
1) Ways in which they are the
same:
2) Ways in which they are
different:
Variation
21/03/2016
Variation means “differences within a species. For example,
consider some of the people in your class:
Ways in which they are the same
Ways in which they are different
Environmental differences
21/03/2016
Some of this variation is due to our parents, but some of it is
due to our upbringing and the environment in which we live –
this is called “Environmental variation”.
Variation due to
inheritance only
Variation due to
environment only
Variation due to a
bit of both
Genes, Chromosomes and DNA
21/03/2016
Humans have 23 pairs of chromosomes. Different species
Sexual Reproduction
21/03/2016
We have similar characteristics to our parents due to genetic
information being passed down in genes through gametes:
The human egg
and sperm cell
(“GAMETES”)
contain 23
chromosomes
each.
When fertilisation happens the
gametes fuse together to make
a single cell called a ZYGOTE.
The zygote has 46 chromosomes
(23 pairs) and contains
information from each parent.
Sexual vs. Asexual reproduction
21/03/2016
Sexual reproduction:
•2 parents are needed
•Offspring will have “pairs” of chromosomes
•This will cause genetic variation
Asexual reproduction:
•Only 1 parent needed
•Offspring are GENETICALLY IDENTICAL to
parent (“clones”)
“Snuppy” – the
first cloned dog
(Aug 05)
Boy or Girl?
X
Y
21/03/2016
X
“Allele”
Girl
XX
XY
Boy
Mother
Boy or Girl?
21/03/2016
Son
Father
Daughter
Genotype
Phenotype
Key words
21/03/2016
•This allele determines the development of a
characteristic
•The characteristic caused by the genotype
Allele
•This allele will determine a characteristic only if
there are no dominant ones
Dominant
•This word refers to a pair of chromosomes being
made of two different alleles of a gene
Recessive
•The genetic make up in a nucleus
Homozygous
•This word refers to a pair of chromosomes being
made of two of the same alleles of a gene
•An alternative form of a gene
Heterozygous
Eye colour
21/03/2016
In eye colour the brown eye allele is dominant, so we call it
B, and the blue eye is recessive, so we call it b:
BB
Bb
bb
Homozygous
brown-eyed
parent
Heterozygous
brown-eyed
parent
Blue-eyed parent
What would the offspring have?
Eye colour
Example 1: A homozygous
brown-eyed parent and a
blue-eyed parent:
X
BB
Parents:
Gametes:
21/03/2016
Example 2: 2 heterozygous
brown-eyed parents
bb
Bb
X
Bb
B
B
b
b
B
b
B
b
Bb
Bb
Bb
Bb
BB
Bb
bB
bb
(FOIL)
Offspring:
All offspring have brown eyes
25% chance of blue eyes
Eye colour
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Example 3: A heterozygous brown-eyed
father and a blue-eyed mother:
Bb
bb
B
b
b
b
Bb
Bb
bb
bb
Equal (50%)
chance of
being either
brown eyed or
blue eyed.
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Another method – the “Punnett square”
Example 3: A heterozygous brown-eyed
father and a blue-eyed mother:
B
b
b
Bb
bb
b
Bb
bb
Father
Mother
Example questions
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1) In mice, white fur is dominant. What type of offspring
would you expect from a cross between a heterozygous
individual and one with grey fur? Explain your answer with a
genetic diagram.
2) A homozygous long-tailed cat is crossed with a homozygous
short-tailed cat and produces a litter of 9 long-tailed kittens.
Show the probable offspring which would be produced if two
of these kittens were mated and describe the characteristics
of the offspring (hint: work out the kitten’s genotype first).
Inherited diseases
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1) Cystic fibrosis – a disease that causes thick and sticky mucus to coat
the lungs, gut and pancreas, making breathing and digestion difficult. It’s
caused by faulty recessive alleles:
Ff
X
Ff
2) Huntingdon's disease – a disease of the nervous system that causes
shaking, memory loss, mood changes and eventually dementia. It’s caused
by a faulty dominant allele:
Cc
X
cc
3) Sickle cell anaemia – a disease that alters the shape of red blood cells,
thereby reducing their oxygen capacity, causing weakness and anaemia.
It’s caused by recessive alleles:
Ss
X
Ss
Family Pedigree Charts
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Consider the following chart of the offspring and
grandchildren between two sickle-cell anaemia carriers:
Key:
= male
= female
= S allele
= s allele
Q. Describe the genotype and the phenotype of each
of the grandchildren. Also, which member of this
family has got sickle-cell anaemia?
The debate over genes
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The “Nature vs Nurture” debate is all about whether or not
certain attributes or abilities are down to genetic reasons or
through upbringing, e.g.:
Sporting ability
Good health
Intelligence