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We are learning today about
Why you are you!
23/05/2017

What am I looking for?
•Can we all recall the terms gene, allele and
characteristics?(Pass)
•Can most of us use a Punnett square?(Merit).
•Can some of us use Pedigree Analysis? (Distinction)
word bank available
1

Kate and her
sister have
similar
features.
Baby George
will inherit
some of
them.
Biological families have characteristics in common because
we inherit genes from each parent. Different forms of the
same gene are called alleles. Combining the alleles gives us
our characteristics.
Monohybrid inheritance
2

Zag and Pod are aliens. They want to have offspring.
It is important to Zag that some of their offspring have
yellow antennae like her.
Their antennae colour is controlled by just one gene.
Passing on a characteristic controlled by one gene is called
monohybrid inheritance.
Monohybrid inheritance
2
The two versions of the antennae gene (the alleles) are,
C – blue allele
c – yellow allele
Zag and Pod inherited one allele from their mother and
one from their father.
Zag inherited c(mother) and c(father)
so she is cc
Pod inherited C(mother) and C(father)
so he is CC

Remember last lesson?
2 
Two of the same allele (version of a gene) = homozygous
Zag’s genotype is cc = homozygous
Her phenotype is yellow antennae
Pod’s genotype is CC = homozygous
His phenotype is blue antennae
Quad has two different alleles = heterozygous
Quad’s genotype is Cc = heterozygous
Monohybrid inheritance
6
We can use a Punnett square to find out the chances of
their offspring having yellow antennae.
father’s
genotype
C
C
c
Cc
Cc
c
Cc
Cc
mother’s
genotype

c
c
C C
Cc Cc
Cc Cc
CC
= blue
cc
=yellow
but all the offspring are
3
Cc
What colour will their antennae
will be?
In fact they will have blue antennae.
The Blue allele is described as DOMINANT.
Even if the blue gene is inherited from only one parent
that colour will take over.
Genotype
Cc gives phenotype blue antennae
The yellow allele is RECESSIVE.

So Pod is obviously not what Zag is looking for!
2

What about Quad? He has genotype Cc.
father’s
genotype
mother’s
genotype
C
c
c
Cc
cc
c
Cc
cc
but now two offspring,
(50% chance), have
yellow antennae.
as before two offspring ,(50% chance),
have blue antennae.
Lan has genotype Cc and so has blue antennae.
2

What would Quad’s offspring with Lan be?
Fill in the square on your
sheet
and of
find
out
3 out
4 offspring
father’s
genotype
mother’s
genotype
C
c
C
CC Cc
c
Cc
cc
have blue antennae.
-75%
This relationship could
produce a yellow
antennae offspring, but
it is less likely -25%
The Punnett square only tells you the chance that
each offspring will have the characteristic.
If the Quad and Lan had offspring there is a 25%
chance for each one that they will have yellow
antennae.
The square does NOT say that if they had 4 offspring
3 would definitely have blue antennae and 1 would
have yellow.
Summary
9

characteristics are inherited from our
Some of our ..............................
genes We inherit one version of the
parents through our .............
one from our father.
allele – from our mother and ........
gene – ............
If we inherit the same allele from both parents our
homozygous
genotype is ........................
If we inherit different versions of the gene our genotype
heterozygous
is ...........................
dominant
The alleles for each characteristic can be ..................
recessive (lower case letter)
(capital letter) or.....................
dominant allele will always ‘win’.
The ...................

Have a go at the question on the worksheet.
Get back to work!!
Mutations
Our genes and chromosomes are made of DNA.
Sometimes the code it contains has been changed.
E.g. the base pairs might be in a different order.
This different code means that the gene might produce
a different effect. This change in code is called a
mutation.
Some mutations can be useful – beneficial
Some mutations dangerous - harmful
http://www.bbc.co.uk/learningzone/clips/mutations-and-genetic-diseases/10653.html

Sickle Cell Disease.
4

Sickle cell disease is caused by a mutation in the gene that
controls making haemoglobin (the chemical that carries
oxygen in your blood).
Think about this couple who are thinking of starting a
family.
Mum: genotype - Rr
phenotype unaffected carrier
A carrier is someone who can pass on the disease but
doesn’t have it themselves.
Dad: genotype - Rr
phenotype unaffected carrier
On your sheet fill in the Punnett square for the
couple to show their chances of having children with
sickle cell disease.
father’s
genotype
mother’s
genotype
R
3

r
R
RR Rr
r
Rr
rr
So, for this couple the chance of having a child with sickle
4 or 25%.
1 in ........
cell disease is .......
50
The chance of being a carrier is ..............%
Here is another type of genetic diagram to show this. 1

Fill in the
details on
your sheet.
What if one of the parents has the disease and the
other is a carrier?
father’s
genotype
r
r
Rr
Rr
Fill in the punnet
square on your sheet
mother’s
genotype
R
r
rr
rr
The chances of their
child having sickle cell
is 50% (2 in 4 or 1in 2)

What if one parent has the disease but the other isn’t
even a carrier?
r
R
r
R
r
R
r
R
r
R
R
r
Now all the children are carriers but none of them has
sickle cell disease.

4
Pedigree Analysis.
2

The inheritance of a particular characteristic in a family
can be studied using a pedigree chart.
male
carrier
female
carrier
fully shaded = with disease
?
half shaded = carrier
carrier
carrier
carrier
carrier
Is Theo a carrier, a person who has sickle cell or an
unaffected person?
23/05/2017

What am I looking for?
•Can we all recall the terms gene, allele and
characteristics?(Pass)
•Can most of us use a Punnett square?(Merit).
•Can some of us use Pedigree Analysis? (Distinction)
word bank available