1. Mutations Chapter 12

2. Mutations Chapter
To investigate mutations and chromosome abnormalities, specifically ....
Alteration of base type or sequence.
Non-disjunction and its effects on human
You should be able to examine photographs of karyotypes of individuals and recognise conditions such as
Down’s Syndrome
Turner’s Syndrome
Kleinfelter’s Syndrome

3. Mutations
A mutation is a change in the structure or amount of an organisms genetic material.
This mutation can by a tiny change in DNA structure or can be a large scale change in chromosome structure or number
When a change in genotype produces a change in phenotype, the individual is called a mutant

4. Vocab
Phenotype: individual's observable traits Ex. such as height, eye color, and blood type
Genotype: individual's collection of genes Ex. XX or XY
Karyotype: is the number and appearance of chromosomes in the nucleus of a eukaryotic cell

5. Gene Mutations = Alteration of the base or sequence
A change in one or more of the nucleotides in a strand of DNA
There are four main types of mutation
POINT MUTATIONS
Substitution Mutations
Inversion Mutations
FRAMESHIFT MUTATIONS
Insertion Mutations
Deletion Mutations
More specifically each of the has had an alteration in one or more codons for one or more specific amino acids leading to a change in the protein that is synthesised.

6. Point mutations (substitution and inversion)
For a protein to work properly it must have the correct sequence of amino acids.
If there is a substitution or inversion mutation it usually brings about a minor change (i.e. one different amino acid). Organism is affected only slightly or not at all.
However if the substituted amino acid occurs at a critical point in the amino acid a major defect may arise.
(e.g. Formation of haemoglobin S in sickle cell anaemia.)

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8. Substitution – one base is swapped for another – e.g. U for C

9. Another example!

10. Substitution another example
Dr. Cocozza is crazy! ATG TCA AAT CGA Dr. Cocozza is ______! ATG TCA AAT GGA

11. Inversion
Inversion of two or more nucleotides, i.e. Positions become back to front (inverted)!

12. Frameshift Mutations - (Insertions or deletions)
Here a there is a major change, since it leads to a large portion of the gene’s DNA to be misread.
This results in the produced protein differing from the normal protein by many amino acids which is usually non-functional.
e.g. If a protein is an enzyme which catalyses an essential step in a metabolic pathway, then the pathway becomes disrupted, for example PHENYLKETONURIA.

15. Albinism

16. Frameshift example

17. Frequency of mutation
In the absence of outside influences, gene mutations arise spontaneously and at random but occur rarely.
Mutation rate varies from species to species, allele to allele.
Most mutant alleles are recessive – expressing themselves when two recessive alleles meet in future generations.
However a few mutant alleles are expressed by the first generation to inherit them because they are either dominant (e.g. Huntington's Chorea) or sex linked (e.g. haemophilia).

18. Mutagenic agents – Increases mutation rate.
These include
A variety of chemicals act as mutagens. E.g.
Bromouracil, are structurally similar to DNA bases, and are inserted in place of normal bases.
Ethidium bromide has a structure that allows it to wedge within the DNA double helix
Peroxides and mustard gas, chemically modify DNA.
Exposure to high-energy radiation (bombardment by alpha, beta, or gamma particles) or ultraviolet light can have a similar effect.

19. Example of chemical mutations
Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

20. The Chernobyl Babies – Radiation causes birth defects
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Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

21. Chromosomal Anomalies
Gamete: A cell whose nucleus unites with that of another cell to form a new organism (egg and sperm). A gamete contains only a single (haploid) set of chromosomes. Haploid means ½ the total amount of genetic material needed.
Meiosis: a type of cell division in which a nucleus divides into four daughter nuclei, each containing half the chromosome number of the parent nucleus: occurs in all sexually reproducing organisms in which haploid gametes

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23. Chromosomal Abnormalities
Chromosomes can be affected by mutations which bring about large scale changes to the genetic material.
One type happens during meiosis in humans when unusual gametes can be formed which contain 22 or 24 chromosomes instead of the normal 23
This leads to the formation of zygotes with abnormal chromosome complements.
This is called non-disjunction

24. Non-disjunction during meiosis.
These abnormal gametes are formed when a spindle fibre fails and one of the pair of homologous chromosomes fail to become separated
Extra copy
Extra copy
Lack a chromosome
Lack a chromosome
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Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

25. Down’s Syndrome
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26. Down’s Syndrome Due to non-disjunction of chromosome 21.
Abnormal egg (n=24) + normal sperm (n=23) abnormal zygote (n=47).
An extra copy of chromosome 21 is seen in the karyotype of someone with Down’s syndrome
The affected individual is characterised by mental retardation and distinctive physical features
Egg mother cells of older women (80% due to maternal age) tend to be more prone to non-disjunction at meiosis.
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27. Down’s Syndrome (aka 21) Karyotype
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28. Turner’s Syndrome
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30. Turner’s Syndrome – female only
If a gamete which possesses no sex chromosomes meets and fuses with a normal X gamete, the zygote formed has the following chromosome complement - 2n = 44 + XO
Individuals are always female and short in stature
Their ovaries do not develop so they are infertile and fail to develop secondary sexual characteristics e.g. breast development and menstruation.
Happens 1:2,500 live births
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31. Turner’s Syndrome
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32. Klinefelter’s Syndrome
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33. Klinefelter’s Syndrome- Male Only
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34. Klinefelter’s Syndrome – Male only
Happens when:
An XX egg is fertilised by a normal Y sperm
OR an normal X egg is fertilised by an XY sperm
Resulting with chromosome complement 2n = 44 + XXY
Individuals are always male and possess male sex organs
However they are infertile since their testes only develop to half the normal size and fail to produce sperm
Testes produce low levels of testosterone so facial hair, deepening of voice are only weakly expressed. Some sufferers develop small breasts.
Occurs in 1:1,000 live male births
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36. Chromosome Mutations
Changes in number and structure of entire chromosomes
Original Chromosome ABC * DEF
Deletion A_C * DEF
Duplication ABBC * DEF
Inversion AED * CBF
Translocation ABC * JKL
GHI * DEF

37. Remember… There are two ways in which DNA can become mutated:
Mutations can be inherited.
Parent to child
Mutations can be acquired.
Environmental damage
Mistakes when DNA is copied
They can be harmful, helpful or neutral.

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