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					               Alford Academy




                Higher Biology

     Unit 2: Genetics and Adaptation




                  Mutations
                  Chapter 16

                     Mutation
Name: __________________ Teacher: ________________
                                       Mutation
A mutation is defined as a change in the structure or quantity of genetic material in
an organism. Mutations are very rare events and most are harmful. However
variations which allow a population to adapt to a changing environment are the
result of mutations.

Without mutations all individuals would be homozygous and no variations would
exist. Harmful mutations tend to be eliminated from a population by selection
against them.

Most mutations are recessive and are therefore not expressed until two occur
together in the homozygous recessive individual. When such a change occurs and
the individual expresses the mutation in the phenotype that individual is known as
a mutant.

     Mutations can occur randomly.
     Mutations are relatively rare.
     Mutations occur naturally.

The rate at which mutations occur can be increased by using mutagenic agents.

Examples of mutagenic agents:

     Certain chemicals e.g. lead oxide, mustard gas
     Radiation e.g. UV-light, x-rays and gamma rays.

                              Types of Mutations

There are 3 types of mutations. These are:

     Gene Mutations.
     Changes in the chromosome number
     Changes in the structure of one chromosome

Changes in the number of chromosomes within a cell

This is due to the failure of the spindle to form properly which prevents the
separation of the chromosomes during meiosis. This may effect one chromosome e.g.
Down's Syndrome, or may be complete spindle failure as seen in polyploid plants.
Failure of spindle formation is called non-disjunction.

                                         -2-
                               Non-Disjunction
This is a chromosome mutation caused by spindle failure.

Non-disjunction results in the addition or loss of one or more chromosome.

During meiosis, homologous chromosomes come together and then segregate into
separate cells. The gametes therefore end up with one of each type of
chromosome.

Label the diagrams on the next page fully to show the difference between
normal meiosis and meiosis where non-disjunction has occurred.




                                       -3-
                               Down's syndrome

Down's Syndrome is due to non disjunction resulting in an individual with an extra
chromosome 21. The affected individual is mentally retarded and has distinct
physical features.

A karyotype is a display of matching chromosomes showing their number, form and
size.

Look at the karyotypes of a normal individual and a Down's syndrome individual.
Which is which? Underneath each karyotype comment on whether it is normal or
down’s and explain your choice.




Answer the questions below:

1. Explain how the differences are produced.



2. What is Down's syndrome caused by the presence of?




Now answer TYK questions 1-3 page 112 (old), page 124 (new)
     YOU DO NOT NEED TO LEARN THE INFORMATION ON
                      THIS PAGE!


Non-Disjunction of the sex chromosomes

Turner’s Syndrome

No sex chromosome fuses with normal X gamete.
Zygote chromosome complement 2n = 45 (44 + X)



                                 Individuals are always Female.
                                 They are infertile – ovaries fail to
                                 develop normally.




Klinefelter’s Syndrome

XX egg fertilised by normal sperm Y, or normal X egg is fertilised by an XY sperm.
Zygote formed 2n = 47 (44+XXY).




                                             Individuals are always male
                                             and have male organs. They
                                             are infertile – testes develop
                                             to half normal size and fail to
                                             produce sperm.




                                       -5-
                    ‘Complete’ non-disjunction or polyploidy
This is due to the failure of all spindle fibres during meiosis in a gamete mother cell.
This results in 2 gametes which are diploid and two with no chromosomes.

Complete non-disjunction will result in diploid gametes i.e. they have two of each
chromosome instead of one of each pair (the gametes which gain no chromosomes
will die)
                    Diagram showing complete non-disjunction

                                                         Diploid gametes 2n
                         All chromosomes go
                         into one cell

                                                  Mitotic Division




                       Meiotic Division



  Diploid Gamete
   Mother Cell

                                                               Gametes without
                                                               chromosomes die

If a diploid gamete (2n) fuses with a normal haploid gamete (n) a triploid (3n)
individual is formed. This individual has three sets of chromosomes.



Complete the diagram below by inserting the chromosomes, showing the joining
of a ‘2n’ gamete with an ‘n’ gamete where n=2.


                                            -6-
  2n
gamete

                                                   Cell Division
                  
     n
  gamete                                                        Sterile organism


If the diploid gametes are fertilised by a normal haploid gamete a triploid known as a
polyploidy plant is produced.

The organism shown above cannot produce gametes and is therefore sterile, as
meiosis cannot occur because homologous pairs cannot be formed.

If two diploid gametes fuse a tetraploid (4n) individual is formed. The organism has
four sets of chromosomes. It is fertile as they are able to form homologous pairs.

Often these polyploidy plants have an economical advantage, for example they
may have/be:

        Larger plants
        Increased seed and fruit size
        Resistance to disease
        Increased yield
        Hybrid Vigour (better in some way than the parent plants)

Example of Polyploidy

An example of polyploidy is in the species of grass, Spartina townsendii, which is
formed by crossing Spartin stricta and Spartina alterniflora.

Spartina townsendii is fertile but it is formed as a result of the cross between S.
stricta and S. alterniflora which are two different species.

Remember: When two different species are crossed the resulting offspring
should not be fertile!

                                         -7-
Complete the polyploidy example below by inserting the correct numbers for the
haploid and diploid state.
                               Polyploid example

                  Spartina                            Spartina
                   stricta                            alterniflora
                       2n=56                           2n=72
                         n=                               n=
                                  Sterile Hybrid
                                        2n=
                                  Spindle failure
                                 causing polyploidy
                                         
                                      Spartina
                                     townsendii
                                        2n=
                                        n=
Explain why the hybrid is sterile.


                               Chromosome Mutations

Chromosome mutations involve the change in the structure of one chromosome;
they involve a change in the number or sequence of genes in a chromosome.

The following are 4 types of chromosome mutations:

     Inversions
     Deletions
     Translocations
     Duplications.

The table on the next page tries to demonstrate this by giving each gene on a
chromosome a letter or number.




                                          -8-
  Normal         Type of
                                      Altered chromosome             Effects
chromosome       mutation
                                             1234678
                 Deletion
                                         gene 5 is missing
                                              12345                  Terminal
                                            ABCDE678                or harmful
               Translocation
                                One section of chromosome joins
 12345678                            to another chromosome
                                            12543678
                 Inversion      a segment of chromosome breaks
                                                                     May be
                                off, turns around and joins again
                                                                    beneficial
                                           1234565678
                Duplication
                                 sets of genes become repeated

                            Chromosome Mutations

Each of the diagrams below on the next page, represent a type of chromosome
mutation. For each, name the type of mutation and briefly describe what has
happened.




                                             __________________
                                             _________________________
                                             _________________________
                                             _________________________
                                             _________________________
                                             _________________________
                                             _________________________



                                     -9-
     _________________
     ___________________________
     ___________________________
     ___________________________
     ___________________________
     ___________________________
     ___________________________

    _________________
    ___________________________
    ___________________________
    ___________________________
    ___________________________
    ___________________________
    ___________________________

     __________________
     ____________________________
     ____________________________
     ____________________________
     ____________________________
     ____________________________
     ____________________________

- 10 -
                                 Gene mutations
Gene mutations involve a change in one or more nucleotides, which change gene
structure.

One amino acid change can have a huge effect on the protein shape. In the following
messages each letter represents a nucleotide.

Think about this in terms of a sentence. Highlight the changes and beside each say
what the change is.
1)   Normal message:       There is a big graph on the wall.
     Mutated message:      There is a big grape on the wall.

2)   Normal message:       Your arms look swollen.
     Mutated message:      Your rams look swollen.

3)   Normal message:       Look at the steam on the window.
     Mutated message:      Look at the stream on the window.

4)   Normal message:       I hate wasps, they sting badly.
     Mutated message:      I hate wasps, they sing badly.

Each of the diagrams below and on the next page, represents a type of gene
mutation. The letters represent nucleotides along the strands of DNA and
mRNA.
For each gene mutation below, name the type of mutation, briefly describe what has
happened and say whether it is a point or a frameshift mutation.




_______________________________________________________________________________
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_______________________________________________________________________________
_______________________________________________________________________________

                                        - 11 -
                         Gene Mutations cont…




_______________________________________________________________________________
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_______________________________________________________________________________




_______________________________________________________________________________
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  1. Complete the following diagram on the next page by inserting the
      appropriate letters
     (normal and mutant mRNA).
                            Normal       Mutant

                DNA
                              C T T            CA T
Transcription                                            Substituted
                                                          nucleotide
                                      - 12 -
              mRNA

  Translation

          Amino Acids         Glutamic acid      new amino acid

a) Complete the following sentence:

The example of a gene mutation, shown above, is called ________________. It is

where one _________________ is replaced by a different _________________.

b) How will this mutation affect the protein molecule produced?



2. Complete the diagram by inserting the normal and mutant mRNA and add in
   the names of amino acids made (see amino acid table on page 319 (old), page
   353 (new) of your textbook).

                     Normal                               Mutant


  DNA         AGAG T CG GG GA T                    AGA TG C GGG GA T
  A
Transcription


  mRNA
  AA
Translation

  Amino
  Acids



                                        - 13 -
a) Complete the following sentence:

The example of a gene mutation, shown above, is called gene ________________.

It is where _____________________________________.

b) What effect does this mutation have on the amino acids in the protein
   molecule?

3. Complete the diagram by inserting the normal and mutant mRNA and add in
   the names of amino acids made:

                     Normal                              Mutant


  DNA         AGAG T CG GG GA T                  AGA GTT C GGG GA
  A
Transcription


  mRNA
  AA
Translation

  Amino
  Acids




a) Complete the following sentence:

The example of a gene mutation, shown above, is called gene ________________.

It is where _____________________________________.
                                        - 14 -
b) What effect does this mutation have on the amino acids in the protein molecule?



4. Complete the diagram by inserting the normal and mutant mRNA and add in
   the names of amino acids made:

                     Normal                              Mutant


  DNA         AGAG T CG GG GA T                  AGA TC GG GG A TG
  A
Transcription


  mRNA
  AA
Translation

  Amino
  Acids

a) Complete the following sentence:

The example of a gene mutation, shown above, is called gene ________________.

It is where _____________________________________.

b) What effect does this mutation have on the amino acids in the protein molecule?




Work in groups to come up with an easy way to remember gene and chromosome
                                  mutations!




                                        - 15 -
                 Chromosome and Gene Mutation Questions

1)   With the aid of an example, state clearly the difference between the terms
     mutation and mutant?



2)   What name is given to the process by which a spindle fibre fails during
     meiosis and one or more of the gametes produced receive an extra
     chromosome?



3a) If a normal human sperm fertilises an egg containing an extra copy of
    chromosome 21, what is the diploid number of the zygote formed?




 b) What name is given to the condition suffered by a person who
    develops from an abnormal zygote of this type?




 c) What relationship exists between the age of the mother and the
    incidence of this condition occurring?



4a) What is meant by the term Polyploidy?



b) Explain how a Polyploid Plant containing 3 separate sets of chromosomes
   could have arisen?




c) State 2 ways in which polyploid plants can be of an economic importance.



                                          - 16 -
5)    State the 4 different chromosome mutations




6) What name is given to a change that involves a chromosome breaking in two
   places and a segment of genes dropping out?



7)    Name the type of change that involves a chromosome breaking in two places
      and then the affected length of genes rotates through 180°C before
      rejoining?



8)    Name the type of change that involves a section of one chromosome
      breaking off and joining onto another non-homologous one?



9)    Name the 4 different gene mutations



10) Classify these four gene mutations into "frameshift" and "point" mutations




11)   Is frameshift or point mutations most likely to lead to the formation of a
      protein that is greatly changed and non-functional?



12) Name two mutagenic agents?




Now answer AYK question 4 page 118 (old), page 131 (new)



                                           - 17 -
                              Mutations Dictionary

Chromosome mutations-Can be a change in chromosome number due to spindle
failure during meiosis. Or a change in the structure of a chromosome due to a
change in the number/order of the genes i.e translocation, inversion, duplication and
deletion (TIDD)

Down’s Syndrome-An example of a chromosome mutation involving a change in the
number of chromosomes. Down’s syndrome individuals have 47 chromosomes instead
of 46 due to non-disjunction happening at pair 21.

Frameshift mutations-Type of gene mutations, which lead to a major change in the
gene’s DNA i.e. insertion and deletion

Gene mutations-type of mutation, which involves a change in one or more of the
actual nucleotides in a strand of DNA. Four types of gene mutation are deletion,
insertion, substitution and inversion (DISI)

Karyotype-a display of the complete set of chromosomes (which shows their
number, form and size)

Klinefelter’s syndrome-this is a condition that arises when non-disjunction happens
in the sex chromosomes. An XX egg is fertilised by a normal Y sperm then the
resulting zygote has the chromosome complement 44 + XXY. Such individuals are
always male and possess male sex organs. However they are infertile.
Mutagenic agents-Factors that can artificially increase the rate of mutation e.g.
chemicals (such as mustard gas) and radiation (gamma rays, X-rays and UV light)

Mutant-When a mutation is actually expressed in the phenotype, the affected
individual is called this.

Mutation-A change in the structure or quantity of genetic material in an organism.
Mutation is the only source of new variation




                                        - 18 -
Non-disjunction-this can occur during meiosis and results in gametes with
extra/less chromosomes than normal. During the first meiotic division, spindle
failure results in failure to separate a pair of homologous chromosomes. As in Down’s
syndrome

Point mutations- Type of gene mutations which lead to a minor change in the gene’s
DNA i.e. inversion and substitution

Polyploidy-Rare in animals, more common in plants. When all the spindle fibres in a
gamete mother cell fail during meiosis and none of the homologous pairs become
separated. Results in gametes with double the number of chromosomes. Fertilisation
of these abnormal gametes results in mutant plants which have complete extra sets
of chromosomes.

Sickle cell anaemia-due to a type of gene mutation called substitution that results
in the formation of sickle–shaped red blood cells. An example of when a point
mutation (which is usually not that harmful) can occasionally cause a major defect

Turner’s syndrome- this is a condition that arises when non-disjunction happens in
the sex chromosomes. A gamete with no X/Y chromosomes is fertilised by a normal
X gamete then the resulting zygote has the chromosome complement 44 + XO. Such
individuals are always female and are infertile.




                                        - 19 -
                            Variation – Mutations
                          Activity                              I can find    I can
                                                                this in my   do this
                                                                  notes
State that a mutation is an error in the amount or structure
of genetic material in an organism
State that mutations in nature occur at random and at low
frequency
Define the term ‘mutagen’ and give examples
State that mutations can be grouped under three headings:
1. alteration to the sequence of bases making up a gene
2. alteration to chromosome structure
3. alteration to chromosome number
State that alterations to base sequence can be of 4 types:
Substitution; insertion; deletion; inversion
Describe what is involved in each of the above examples
State the effect of a gene mutation would have on an amino
acid sequence and subsequently a protein

State that alterations to chromosome structure can occur in
one of these ways:
deletion; inversion; duplication; translocation
Describe what is involved in each of the above examples
State that the number of chromosomes in a cell can be
altered by non-disjunction during meiosis/mitosis
Explain what happens to spindle fibres and chromosomes
when non-disjunction occurs
Compare the chromosome number of people with & without
Down’s Syndrome
State that polyploidy arises when non-disjunction involves
whole sets of chromosomes because all the spindle fibres fail
State the benefit of polyploidy to crop breeders
Explain what a karyotype is



                                       - 20 -

				
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