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Higher Biology
Mutations part 1
Mutations
By the end of this lesson you should be
able to:
Start to understand the role of mutations in the
evolution of a new species.
Know about 1 type of chromosome mutation.
Name a human condition caused by non-disjunction.
Understand what is meant by polyploidy
Explain the economic significance of polyploid plants
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What is a mutation?


A mutation is a change in the
structure or quantity of an organisms
genetic material.
Any mutation that occurs in the
gamete mother cells of an organism
can be inherited from one generation
to the next.
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What is a mutation?


When a mutation causes a change in
the genotype that affects the
phenotype- the individual is called a
mutant.
There are 2 main types of mutations.
Chromosome
mutations
Gene
mutations
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Chromosome mutations

There are 2 types of chromosome
mutations.
Change in
chromosome
number
Change in
structure of
one
chromosome
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Change in chromosome number


In meiosis a diploid cell divides to produce
4 daughter cells
Sometimes a pair of homologous
chromosomes fail to separate during the
first meiotic division- this is called nondisjunction.
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Non-disjunction
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Non-disjunction
Torrance
 Read page 109 and study Figure 16.1
 Explain the meaning of non-disjunction in
terms of:
i.
The process during which this can happen
ii.
What happens to the spindle fibre
iii. The effect on a homologous pair of
chromosomes
iv. The effect on the daughter cells.
 Insert & complete the “Non-disjunction”
sheet from your pack.
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Down’s Syndrome
Torrance

Read page 109-110

Describe the characteristics associated with a
person who has Down’s Syndrome.

Explain how the condition arises, in terms of:
i.
The name of the human cell in which the mutation
occurs
ii.
The pair of chromosomes in which non-disjunction
occurs
iii.
The number of chromosomes in the abnormal
gamete
iv.
The number of chromosomes in an affected person
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Down’s Syndrome

Insert & complete the “Down’s Syndrome”
diagram from your pack
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Disorders of Sex chromosomes
Turner’s Syndrome
 Is caused by an absence of one copy of the
X chromosome
 Individuals are
female and XO
 They are short in
height and infertile
(as their ovaries fail
to develop properly)
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Disorders of Sex chromosomes
Klinefelter’s Syndrome
 Is caused by an extra copy of the X
chromosome
 Individuals are
male and XXY
 Individuals are
sterile as their
testis fail to
develop
properly
 Also mental retardation
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Polyploidy


Polyploids are organisms which contain
complete extra sets of chromosomes.
This condition is more common in plants
than animals.
13
Polyploidy
•At A the
strawberry plant
is exposed to a
chemical called
colchicines.
•At B due to the
effect of
colchicines, total
non-disjunction
at meiosis
produces diploid
gametes(2n).
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Polyploidy
•As a result, at C
two diploid
gametes fuse at
fertilisation.
•at D a new plant
develops which
has four sets of
chromosomes
(4n).
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Polyploidy
Torrance
 Read page 111
1.
Explain what happens during complete nondisjunction in meiosis.
2. State the effect of this process on the
resulting gametes.
3. Explain how a polyploid individual can be
formed
4. State the effect of polyploidy in a named
crop plant with respect to:
a.
b.
Resistance to disease
Vigour
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Polyploidy
Torrance
 Read page 111
5. Explain why polyploid plants are often
infertile
6. Describe how 3n and 4n polyploids occur.
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Practice Questions

1.
Torrance
TYK page 112 Q1 -5
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Mutations
Can you do it?
Start to understand the role of mutations in the
evolution of a new species.
Know about 1 type of chromosome mutation.
Name a human condition caused by non-disjunction.
Understand what is meant by polyploidy
Explain the economic significance of polyploid plants
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