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KS4 Biology
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Inheritance
Variation
This describes how the characteristics of organisms vary. Variation can be inherited
or is the result of environmental factors or a mixture of the two. Variation can be
described as continuous or discontinuous.
Continuous Variation
This is used to describe a characteristic that has a range of different values.
E.g. the length of thumbs in the human population.
Discontinuous Variation
This is used to describe a characteristic that has a few or no in-between forms.
E.g. Tongue rolling, either you can roll your tongue or you can’t.
The following are examples of variation in humans; decide whether each one is
probably caused by genes, by the environment or by both. For each one decide
whether it is an example of continuous or discontinuous variation.
Blood Group
Hair Colour
Sex
Ability in Maths
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Height
Eye colour
Activity
Measure the height of each person in your class to the nearest centimeter.
Divide the heights into classes e.g. 120 - 124, 125 – 129 and tally the number of
individuals in each category.
Height Category
Tally
Height Category
Tally
Construct a histogram to display your results. Join the tops of the bars in your
histogram with a smooth curve.
Questions
1.
2.
3.
4.
5.
6.
What does the shape of the curve tell us about the way height varies?
Suggest reasons why the members of your class should vary in height.
What is the average height in the class? Does this correspond to the
tallest bar?
What group(s) contains the largest and fewest numbers of people?
What is the height range (that is the difference between the shortest and
tallest students) in the class?
Is height an example of continuous or discontinuous variation?
Complete a similar survey for tongue rolling.
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KS4 Biology
B14b / Side 1
A Design for Life
Your body is made up of cells.
Each cell contains a nucleus which controls
the cell.
Each nucleus contains lots of thin threads
called chromosomes.
Chromosomes carry information, which
controls how your body works and what you
look like.
There are 46 chromosomes.
They are found in pairs.
One comes from the father and one from
the mother.
Each chromosome is made up of tangled
threads.
Each thread is made up of a molecule called
DNA.
DNA is the chemical which stores coded
instructions.
A gene is a length of DNA.
Genes are coded instructions for making
proteins.
A protein will control a characteristic e.g.
eye colour.
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Complete the following:
Inside the nucleus are structures called _______________. In humans there are
_______________
chromosomes
arranged
in
_______________.
One
chromosome from each pair comes from the _______________ and the other from
the father.
In human sperm cells and egg cells there will only be _______________
chromosomes. When the sperm and egg fuse in the process of _______________
and produces the _______________ the number of chromosomes is restored back
to _______________.
Chromosomes are made up of a chemical called _______________.
This is a
chemical which can store _______________.
A Length of DNA found on a chromosome that contains all the information for making
a protein is called a _______________.
Below is a diagram showing the chromosomes found in a male (left) and a female
(right). Note how they are arranged into pairs.
Highlight a difference between the chromosome pairs of a male and female.
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Genetic Vocabulary
Allele
Different forms of the same gene are known as alleles.
E.g. the gene controlling eye colour has many different forms black, brown, grey,
green and brown etc.
Alleles for the same gene are always written with the same letter.
Dominant
If you inherit two different alleles for a particular gene one may be stronger that
the other. The stronger allele will mask (cover) the affect of the weaker allele.
E.g. Brown eye colour is dominant over blue eye colour.
Dominant alleles are always written with a capital letter. E.g. B for the brown allele
controlling eye colour.
Recessive
This refers to the weaker of two different alleles that may be inherited. Its effect
will be masked by a dominant allele.
E.g. Blue eye colour is always recessive to brown eye colour.
Recessive alleles are usually written with a lower case letter. E.g. b for the blue
allele controlling eye colour.
Questions
1. What alleles will a person have who has blue eyes?
2. What alleles will a Chinese lady have for eye colour?
3. Explain using the terms above why most Eurasian children have brown eyes even if
their father or mother has blue eyes?
Genotype
Refers to the alleles an organism has.
E.g. the genotype for a person with blue eyes will be bb.
Phenotype
Refers to the appearance of an organism.
E.g. An organism with the genotype Bb will have the phenotype brown eyes.
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Homozygote
An organism is described as being a homozygote or being homozygous if it has two
alleles for a gene, which are identical.
E.g. A person with blue eyes, bb, will be described as being homozygous recessive.
Heterozygote
An organism is described as being a heterozygote or being heterozygous if it has two
alleles for a gene which are different.
E.g. A person with brown eyes, Bb, (who had a blue eyed parent) would be described
as being heterozygous.

Complete the following:
Genes that code for the same character are called _________________. In a pair
of alleles one may be ‘stronger’ or ________________ to the other ‘weaker’ allele
which is known as being _______________.
If both alleles are the same the
organism is said to be ________________.
If the alleles are different it is
described as being _______________.

Cross out the incorrect words in the following sentences:
A pea plant with a tall genotype / phenotype could have a genotype / phenotype TT or
Tt.
A tall pea plant with a genotype TT is homozygous / heterozygous dominant.
A tall pea plant with a genotype Tt is homozygous / heterozygous.
A dwarf pea plant with genotype tt is homozygous / heterozygous recessive.

State how many chromosomes are found in the following human cell types:
a.
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Egg
b.
Muscle
c.
Zygote
d.
Sperm
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Predicting the Outcome of a Simple Cross
Remembering from earlier pages that humans have 46 chromosomes that are present
in 23 pairs. When an organism produces gametes (sperm and egg cells) the pairs
separate so that only one of each chromosome goes into a single gamete cell.
Alleles for the same characteristic are always found on the same chromosome pair.
When the pair separates when gametes form only one allele will be present in each
gamete.

1.
2.
Questions
When a male heterozygous for eye colour (Bb) forms sperm cells, what
percentage of his sperm will have a B allele and what percentage will have a
b allele?
When a female homozygous recessive for eye colour forms her eggs, what
percentage of her eggs will have a B allele and what percentage will have a b
allele?
In genetics the probability of the offspring of a mating having a certain genotype can
be calculated using a punnett square.

1.
2.
3.
4.
Look at the diagram below:
What % of the father’s sperm has a B allele?
What % of the mother’s eggs has a b allele?
What is the probability of having a blue-eyed child?
Explain why the couple above may have 6 children but they all have brown
eyes?
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Genetics Questions
1.
In gerbils the allele for brown coat colour is dominant over the allele for black
coat colour.
a.
If the symbol for the allele for brown coat colour is B, and the allele for
black coat colour is b, give the possible genotypes of:
i.
b.
2.
b.
c.
d.
A black gerbil
What will be the phenotype of a heterozygous gerbil?
Suggest suitable alleles for these two alleles (use the same letters one
capital and one lower case).
Write down three possible genotypes of a pea plant.
What will be the phenotype of a heterozygous pea plant?
What will be the genotype of a pea plant with wrinkled seeds?
Dalmatian dogs have spots. The spots may be black or brown. The allele for
black spots is B, and the allele for brown spots is b.
a.
b.
4.
ii.
In peas the allele for smooth seeds is dominant to the allele for wrinkled
seeds.
a.
3.
A brown gerbil
Heterozygous dogs have black spots. Which allele must be dominant?
What is the genotype of a brown spotted Dalmatian?
In rabbits the allele for brown coat colour is dominant to the allele for white
coat colour.
a.
b.
Write down suitable symbols for these two coat colour alleles.
What coat colours would you expect to find in the offspring of a mating
between two white rabbits? Explain your answer fully using a punnett
square.
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5.
B14d / Side 3
c.
What offspring would you expect to find in the offspring of a mating
between a brown homozygous and a white rabbit? Explain your answer.
d.
Two brown rabbits mated. They had 12 babies, 3 had white coats and 9
had brown coats, explain this.
Some people are born with ‘hitch-hiker’s thumb’.
This is caused by a dominant allele H. The diagram at the top of the next page
shows the inheritance of hitch-hiker’s thumb in a family.
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a.
What is the genotype of grandmother A? Explain the reason for your answer.
b.
Use a genetic diagram to explain why some of the children of C and D had a
hitch-hiker’s thumb, but others did not.
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6.
B14d / Side 5
The black panther is a black variety of the spotted leopard. It occurs quite
commonly in dense tropical rainforests. However, it is much rarer in areas of
open grassland where the normal (spotted) form is more common.
The diagram shows the results of a cross between a spotted leopard and a
black panther and it also shows the results of a cross between two of their
offspring (the F1 generation).
Assume that coat colour is controlled by a single gene with two alleles (H and
h), one being responsible for the spotted coat and the other for black coat.
a.
Which one of the alleles H or h controls black coat colour, explain your
answer.
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b.
Write hh, Hh or HH in the boxes on the diagram to show the possible alleles
possessed by each of the animals illustrated.
c.
What is the expected ratio of homozygous to heterozygous individuals in the
F2 generation. Explain your answer.
d.
Black panthers are far more common in the rainforests than in open grassland
explain what you think may be the reason for this?
Summary of Genetic Crosses
If a heterozygous individual is crossed with a homozygous recessive the probable
outcome in terms of phenotype will always be in a 1:1 ratio.
b.
b.
B
Bb
bb
b.
Bb
bb
If two heterozygous individuals are crossed the probable outcome in terms of
phenotype will always be in a 3:1 ratio.
B
b.
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B
BB
Bb
b.
Bb
bb
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Inherited Diseases
Example:
Sickle Cell Anaemia
Affected Populations:
Affects:
African, South Eastern Europeans, Middle Eastern and
South East Asians.
When the red blood cells of people with sickle cell disease don't get
enough oxygen, it causes a change in the shape of the haemoglobin these
cells change shape. They become longer and curved. Some people think
they look like the blade of a cutting tool called a "sickle."
Sickle-shaped
Normal Red Blood cells
Sickle cells can get stuck in blood vessels and keep blood from reaching parts of the
body. This causes pain and can damage the body's internal organs. Blocked blood
vessels in the arms, legs, chest or abdomen can cause strong pain. Children with sickle
cell disease might get more infections because their spleen is damaged by sickle
cells. One of the spleen's main jobs is to protect against infection. When sickle cells
block blood flow to organs and cause pain and other problems, this is called a "sickle
cell crisis," or a "pain crisis."
Inheritance of the Disease
In this disease there are alleles for normal shaped haemoglobin and haemoglobin that
becomes sickle shaped in areas of low oxygen concentration.
Allele for normal haemoglobin = HbA
Allele for abnormal haemoglobin = Hbs
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Interestingly these alleles are codominant which means that if you are born
heterozygous for this condition half of your blood cells will have normal haemoglobin
and half will have abnormal haemoglobin.
A person homozygous for the Hbs allele usually dies early in life and therefore the
spread of the disease involves heterozygous individuals.
A heterozygous individual is said to suffer from sickle cell anaemia.
Questions
1.
What are the chances of producing normal offspring if a sickle cell sufferer
and a ‘normal’ person produce offspring?
2.
What are the chances of producing normal offspring if two sickle cell
sufferers produce offspring?
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Extension
The percentages of adults who are heterozygous for sickle cell anaemia in different
areas are shown in circles on the map of parts of East Africa below. The distribution
of the malarial parasite is also shown.
Explain the distribution of the sickle-cell gene and that of the malarial parasite.
Suggest an explanation for the distribution of the malarial parasite shown on the
map.
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Genetic Engineering
Gene – a section of DNA that codes (contains the information for making) for a
protein.
Genetic engineering describes a process whereby genes are transferred from
organism to another; they may be between the same or different species.
Use the Internet to answer the following:
Describe 2 examples of genetic engineering in animals.
1.
2.
Describe 2 examples of genetic engineering in plants.
1.
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2.
Complete the table to show 3 benefits and three concerns about genetic engineering:
Benefit
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Concern
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Cloning
When one individual plant or animal is cut up and used to make many genetically
identical individuals it is called cloning. Taking some cells from the plant and growing
them on a nutrient jelly in small, sterile pots can be used to clone a plant. This is
called tissue culture.
All the plants produced will be genetically identical to the parent plant and will
therefore show all the characteristics that the parent plant shows.
Oil Palms and Tissue Culture
Oil palm and sunflower oil provide 30% of the world’s supply of vegetable oil.
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Oil palm trees grow in the tropics. The trees vary greatly in the quantity of oil they
produce. Unfortunately even if you breed two high yielding plants together they may
not necessarily produce offspring that produce a lot of oil. When you breed two
plants together the resulting offspring may take up to three years to reach maturity
and produce oil-yielding palms.
Questions
1.
Palm trees have great commercial value importance in Malaysia because they
produce palm oil. Explain how cloning and tissue culture can be used to help the
yield for palm tree farmers.
2.
Imagine that cloning became very common and soon only one variety of palm
trees was grown. What are the dangers of only growing one variety?
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Mutations
A change in the number or kinds of genes in a cell is called a mutation. DNA is a very
stable molecule. It does not change or react with other molecules easily. This means
that the genes in your cells tend to stay the same all your life.
But things do occasionally go wrong and DNA molecules in a cell do sometimes change.
This may happen for no obvious reason or there may be a definite cause, such as
ionizing radiation (e.g. gamma rays, UV light etc.), or the DNA may be damaged when
it is copying itself so that the new DNA is not the same as the original, or
chromosomes may not be shared properly when the gametes are formed.
Most mutations probably go unnoticed, either because the mutant cell is one among
millions of ordinary cells, or because it is destroyed by white blood cells. But some
mutations can cause cancer. Cancer causes cells to divide uncontrollably and form a
tumour. Most mutations cannot be inherited; if they are inherited the mutation
needs to be present in the DNA of the sperm or egg involved.
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Questions
1.
What is a mutation? Give two examples of ways in which mutations may be
caused.
2.
Why is a mutation in a cell of a person’s ovary or testis more likely to have
harmful effects than a mutation in one of the other cells?
Extension
Cancer Prevention
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a.
What are cancers and why can they be so serious?
b.
Smoking can cause several different cancers, but which cancer is it primarily
associated with?
c.
Which component in cigarette smoke is mainly responsible for cancer?
d.
Explain the thinking behind the advice ‘take care in the sun’.
e.
Outline the link between skin cancer and CFC’s (clorofluorocarbons).
f.
Do you think vegetarians tend to have higher or lower rates of cancer than
non-vegetarians, give your reasons?
g.
List three main treatments for cancer.
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