INHERITANCE
Topic 3 - 2015
Year 10 Biology
TOPIC 3 – INHERITANCE
Things to cover:
1. Review of Topics 1-4
2. Genes & alleles
3. Heterozygous & homozygous
4. Genotypes & phenotypes
5. Dominant traits & recessive traits
6. Autosomal & sex-linked traits
7. Mutations
8. Pedigrees
Work to do:
1. Activity – Pedigree – A Family Tree
2. Textbook Qs – Ex2.5 – p77 – Q1-2, 8-9
3. Textbook Qs – Ex2.6 – p82 – Q6-7, 17-19
4. Textbook Qs – Ex2.8 – p92 – Q3-5, 8-10, 11, 13
Ideas to know:
 Gene
 Genotype
 Allele
 Phenotype
 ABO blood grouping
 Complete dominance
 Homologous chromosomes
 Co-dominance
 Gametes
 Carrier
 Heterozygous
 Punnett square
 Homozygous
 Monohybrid cross
 Dominant
 Pedigree chart
 Recessive
 Gender bias in pedigrees
 Base substitution mutation
 Generation skipping in pedigrees
 Frameshift mutation
 Sex linkage
 Insertion
 Haemophilia
 Deletion
 Colour blindness
REVIEW
Topic 1
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DNA is composed of ____________________ .
•
Each nucleotide consists of:
− A ____________________ sugar
− A ____________________ group
− A ____________________ base (_____ types)
•
The nucleotides form chains. Two chains twist to form the ____________________ shape of
the DNA molecule.
•
Chemical bonds hold the DNA molecule together. Strong ____________________ bonds hold
the nucleotides together, while weak ____________________ bonds form between the
bases.
Topic 2
•
DNA is coiled up tightly to form _______________
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There are _______________ of chromosomes in every cell.
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Most of these are _______________ , controlling general characteristics.
•
One pair are the _______________ , controlling both sexual and general characteristics.
•
Cell division is necessary for ____________________, ____________________ and
reproduction.
•
One type of cell division, ____________________, is used in the formation of new body cells.
It is also used by unicellular organisms for ____________________ reproduction. The
__________ daughter cells formed are ____________________ to the parent cell and have
__________ chromosomes.
•
The other type of cell division, ____________________, is used to form sex cells. Another
name for the products of this type of division are ____________________ This process takes
place in the reproductive organs. The __________ daughter cells formed are
____________________ to the parent cell and have __________ chromosomes. They are also
____________________ in size.
•
In order for cell division to occur, the DNA must ____________________ and the
REVIEW
chromosomes must divide equally between the cells.
•
____________________ can occur if this does not happen correctly. For example, disorders
involving additional or missing ____________________.
•
Down Syndrome is one example. This disorder results from the presence of
____________________ Chromosome 21. This is called ____________________ 21.
•
VARIATION
The population of the Earth is more than 6 billion people, and no two individuals (apart from
identical twins) are genetically the same. Why?
•
People are different because they ____________________ ____________________
____________________ (or ____________________) from their parents.
•
Children carry a ____________________ set of ____________________; half from their
mother and half from their father.
•
A person’s unique characteristics are caused by:
− the ________________________________________ they inherited from their
parents (____________________)
− the ________________________________________ in which they developed
(____________________)
•
Some characteristics, such as ____________________ colour and ____________________
shape, are only determined by genes. These are called ____________________
characteristics.
•
Other types of characteristics, such as ____________________ and hair length, are not
inherited but depend on ____________________ ____________________. These are called
____________________ characteristics.
•
Differences in some characteristics are due to a ____________________ of both inherited
and environmental factors. In some cases, it can be difficult to say how much influence each
factor has.
•
The overall appearance of an organism depends on:
1. its ____________________ (inherited characteristics)
2. the effects of the ____________________ in which it lives.
•
All the observable characteristics of an organism are called its ____________________.
•
The full set of genes of an organism is called its ____________________.
•
An organism’s phenotype therefore depends on its ____________________ plus
____________________ ____________________.
VARIATION
•
____________________ ____________________ is the most important cause of
____________________ ____________________ because it mixes up genetic material.
•
During ____________________, homologous chromosomes ____________________
genetic material. They then line up and separate in different ways,
producing a large ____________________ of different
____________________.
•
At ____________________, any male gamete can combine
with any female gamete.
•
All these events occur ____________________ and create
new ____________________ of genetic material.
•
____________________ is the ____________________ in the ____________________ or
____________________ of ____________________ and is therefore another cause of
genetic variation.
•
Mutations can arise ____________________; for example, through the incorrect copying of
base pairs during DNA replication, or the ____________________ distribution of
chromosomes during ____________________ ____________________.
•
Mutations can also be caused by ____________________ ____________________, such as
radiation and certain chemicals. These factors are called ____________________.
•
Some mutations may be beneficial, but many are harmful and increase the risk of diseases
such as ____________________.
GENES & ALLELES
•
The basic ____________________ of ____________________ is the ____________________.
•
A gene is a segment of a ____________________ that contains the ____________________
required to produce a ____________________.
•
There are ____________________ of each chromosome , known as a
____________________ ____________________. Each copy has its own
____________________ of the gene.
•
These versions are known as ____________________.
•
Most genes are controlled by ____________________.
•
Dominant alleles:
− ____________________ expressed in a cell’s ____________________
− only ____________________ of the dominant allele needs to be inherited in order for
it to be expressed
−
•
represented by an ____________________ case letter (eg. _______)
Recessive alleles:
− only expressed in a cell’s phenotype if ____________________ are present
− if only one copy is present, its effect is ‘____________________ by the
____________________ ____________________
− represented by a ____________________ case letter (eg. _______)
•
If the alleles for a characteristic in a homologous pair are the ____________________, the
organism is said to be ____________________ for that characteristic.
•
If there are ____________________ alleles,
the organism is said to be
____________________ ____________________
for that gene.
•
If there are ____________________ alleles,
the organism is said to be
____________________ ____________________
for that gene.
GENES & ALLELES
•
If the alleles for a characteristic in a homologous pair
are ____________________, the organism is said to
be ____________________ for that characteristic.
•
The characteristic ____________________ by heterozygous alleles will depend on which
allele is ____________________ and which allele is ____________________.
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The allele for brown eyes is ____________________over the allele for blue eyes.
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The individual will have ____________________eyes, because the allele for brown eyes
____________________the allele for blue eyes.
TYPES OF INHERITANCE
COMPLETE DOMINANCE:  NORMAL!!!!!
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If the ____________________ allele is present, it will be ____________________
•
eg. Brown eyed allele (B) always expressed when present (BB or Bb)
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Special symbols:
− Choose ____________________
− Use ____________________ (recessive) and ____________________ (dominant)
− eg. BB, bb or Bb  _______________________________________________________
CO-DOMINANCE:
•
There is ________________________________________!
•
The phenotype is a ____________________ of both alleles present
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eg. red allele + white allele = ____________________ phenotype
•
eg. ____________________ blood from combination of A and B alleles
•
Special symbols:
− Choose ____________________
− Use ____________________ for both
− eg. RR, WW or RW  _____________________________________________________
ABO BLOOD GROUPING
•
To determine your blood type, there are three alleles:
− A –____________________
− B -____________________
− O - ____________________
•
The alleles IA and IB are ____________________
•
However, both of these alleles are ________________________________________ over ί
•
This results in ____________________different phenotypes.
Phenotype
or blood group
Type A
Type B
Type AB
Type O
Genotypes
TYPES OF INHERITANCE
AUTOSOMAL INHERITANCE:  NORMAL!!!!!
•
The gene in question is located on an ____________________
•
Traits can be:
− ____________________ ____________________ – meaning that a trait/disorder is
determined by the presence of a dominant allele
− ____________________ ____________________ – determined by the presence of
two recessive alleles
•
Special symbols:
− BB, bb, Bb
SEX-LINKED INHERITANCE:
•
The gene in question is located on a ________________________________________
•
Will generally be on the ____________________, as the Y carries very few genes
•
eg. ____________________, ________________________________________
•
Traits can be:
− ____________________ ____________________ – meaning that a trait/disorder is
determined by the presence of the dominant allele on the X chromosomes
− ____________________ ____________________ – meaning that a trait/disorder is
determined by the presence of one or two recessive alleles on the X chromosomes
•
Special symbols:
− Females:
•
Homozygous
__________ __________
•
Heterozygous
__________
− Males (only one X chromosome):
•
Unaffected
__________
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Affected
__________
CARRIERS:
•
Someone who is ____________________ for a genetic
disorder
•
They ____________________ the disorder themselves
•
However, the disorder can be ____________________
to the next generation
GENETIC MUTATIONS
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Genes are nearly always passed from parent to offspring _____________________________.
•
Occasionally a _________________ will occur in a gene.
•
This is called a _________________ _________________.
•
_________________ _________________:
– one base is _________________ for another
•
_________________ _________________:
– _________________
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insertion of one or more bases
– _________________
•
deletion of one or more bases
•
•
Why?
– Mutation involves a part of the DNA which that particular cell ____________________
– Mutation occurs but the code
still results in the same __________________________________ & therefore the
same _________________
•
Generally, _________________ mutations are more serious.
PUNNETT SQUARES
•
Also called _________________ _________________
•
Method used to find the _________________ genotype and phenotype ratios of
_________________ when the parental genotypes and/or phenotypes are known.
•
Steps:
1. Write down the _________________ _________________
You may need to choose letter to represent your trait
– choose easy ones like T, G, H not C, S, Y
2. Write down the _________________ _________________ that they are able to pass on
in their gametes (sex cells)
3. Construct the Punnett square
4. Fill in the _________________ _________________ of the offspring
5. Determine the _________________ _________________ of the offspring
6. Determine the _________________ _________________ of the offspring
PUNNETT SQUARES
•
Example:
An alien that is homozygous dominant for green skin has chosen an alien who has purple skin
for his bride. Determine the likelihood that their children will have purple skin.
Like in Maths – you need to state what symbols you will be using to
represent your traits:
eg. Let G = green; g = purple
•
Example:
One of the couples sons (Neyp) married a female alien who was homozygous recessive for the
skin colour trait.
Work out the genotype and phenotype percentage of their potential offspring.
PUNNETT SQUARES
•
Example:
One of Neyp’s sons married a female alien who was homozygous for haemophilia.
Calculate the likelihood that they could have a child with haemophilia.
Again – specify your symbols!
It is a sex-linked recessive disorder!!!
So: Let H = _________________; h = _________________
PEDIGREE CHARTS
•
Shows the members of a family and how they are _________________ to each other.
•
A ___________________________________________________!
•
Pedigree charts can also be used to _________________ the _________________ of a
_________________.
•
Circles = _________________
•
Squares = _________________
•
Shading = _________________ individuals
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Parents = linked by a _________________ line
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Children = _________________ lines running down from parents
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Siblings = linked by a _________________ line _________________ them
PEDIGREE CHARTS
•
Example:
Draw a pedigree chart for Neyp and his wife Gjup., including their parents and children. They
had 3 children, 2 boys and a girl. Their daughter Hefg had purple skin and married an alien
who also had purple skin. They had one son – Yerg. Their son Guol had green skin and was
also married with one purple daughter, Zcug.
Remember, being purple is the recessive trait!
•
Pedigree charts can also be used to determine if:
– The characteristic is _________________ or _________________.
– The characteristic is _________________ or _________________.
•
Things to look for:
– Gender bias of males:females
– Affected offspring from unaffected parents
– Affected sons from affected fathers
PEDIGREE – A FAMILY TREE
Make your own family tree for one trait of your choosing (eye colour, natural hair colour, or blood type).
Include as many people on your immediate family as possible and use all of the rules for pedigrees. Identify
the names and genotypes of all individuals in your pedigree.
Attach answers to textbook Qs to the back of the booklet