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Higher Human Biology. Unit 1: Cell Function and Inheritance. Chapter 13: Mutations and Chromosomal Abnormalities. Learning Intentions. To investigate mutations and chromosome abnormalities, specifically .... Alteration of base type or sequence. Non-disjunction and its effects on human - PowerPoint PPT Presentation
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Chapter 13: Mutations and Chromosomal Abnormalities
Higher Human Biology
Unit 1: Cell Function and Inheritance
21/04/23 1Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Learning Intentions• 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
21/04/23 2Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
You need to know these words
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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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
21/04/23 4Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Gene Mutations = Alteration of the base or sequence
• Here there is a change in one or more of the nucleotides in a strand of DNA
• There are four main types of mutation
– POINT MUTATIONS
1. Substitution Mutations
2. Inversion Mutations
– FRAMESHIFT MUTATIONS
3. Insertion Mutations
4. 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.
21/04/235Mrs Smith: Ch13: Mutations an
Chromosomal Abnormalities
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).Here 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.
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Substitution – one base is swapped for another – e.g. U for C
21/04/23 7Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Inversion• Inversion of two or more nucleotides, i.e. Positions become back to front
(inverted)!
21/04/23 8Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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 ctalyses an essential step in a metabolic pathway, then the pathway becomes disrupted, for example PHENYLKETONURIA.
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Insertion
21/04/23 10Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Insertion
21/04/23 11Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Deletion
21/04/23 12Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Phenylketonuria
Background to Phenylketonuria
Phenylalanine and tyrosine are two amino acids that humans obtain from protein in their diet. During normal metabolism, excess phenylalanine is acted upon by an enzyme (phenylalanine hydroxide).
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Phenylketonuria: aka - PKU
• PKU is a hereditary disorder caused by a genetic defect which disrupts this metabolic pathway.
• An affected person lacks the normal allele of the gene required to make the enzyme Phenylalanine Hydroxide
21/04/23Mrs Smith: Ch13: Mutations an
Chromosomal Abnormalities14
Phenylketonuria: Continued
• Owing to this inborn error in metabolism, phenylalanine is no longer converted to tyrosine.
• Instead it undergoes alternative pathways which produces toxins which affect the metabolism of brain cells and severely limit mental development.
21/04/23Mrs Smith: Ch13: Mutations an
Chromosomal Abnormalities15
Screening for PKU – More in chapter 14
• In Britain, newborn babies are screened for PKU, and sufferers are put on a diet containing minimum phenylalanine.
• As a result the worst effects of PKU can be kept to a minimum.
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Albinism
• Albinism results from a mutation which prevents the formation of enzyme 3 (Melanocyte Tyrosinase). As a result albinos fail to synthesise melanin.
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Albinism – the symptoms• Due to the total lack of the pigment melanin Albino’s have
characteristic– Very pale skin which fails to tan.– White hair– The colour of the iris is usually blue/gray or light brown with
some people having a reddish or violet hue reflected through the iris.
– In some cases there is vision problems.• They must avoid ultraviolet radiation and may require to ware
tinted glasses to assist with photophobia.
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Albinism
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Cystic Fibrosis• Mucus is a slimy substance secreted
by the inner lining of the wind pipe and intestine.
• Mucus is made of a glycoprotein which makes it thick, slimy and perfect for protection and lubrication.
• The genetic information for coding this glycoprotein is on chromosome 7.
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Cystic fibrosis: due to gene mutation
• If the info on the gene for the glycoprotein is altered.... Two outcomes.....1. Homozygous for the mutant allele: Make
abnormally thick and sticky mucous leading to lung congestion and blockage of the pancreatic duct = CYSTIC FIBROSIS.
• 1:2500 births in Britain
2. Heterozygous for the mutant allele: they carry the mutant allele masked in their genotype
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Cystic fibrosis
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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).
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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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.
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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Example of chemical mutations
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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The Chernobyl Babies – Radiation causes birth defects
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Task: Torrance pg 97 Qu’s 1-4
21/04/23 27Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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
21/04/23 28Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Extra copy
Lack a chromosome
Lack a chromosome
Extra copy
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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.
21/04/23 30Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Down’s Syndrome (aka 21) Karyotype
21/04/23 31Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Symptoms of Down’s
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Non-disjunction of Sex Chromosomes
If human sex chromosomes are affected by non-disjunction during meiosis then unusual gametes are formed.
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Normal situation
Abnormal situation
Egg mother cell.
Normal Meiosis
Non-disjunction at 1st meiotic division
22+ X
22+ X22+ X
22+ X 22+ XX
22+ XX 22
22
Normal eggs Abnormal eggs
Normal situation
Abnormal situation
Spermmother cell.
Normal Meiosis
Non-disjunction at 1st meiotic division
22+ X
22+ Y22+ X
22+ Y 22+ XY
22+ XY 22
22
Normal sperm Abnormal sperm
44+ XX 44+ XX 44+ XY 44+ XY
21/04/23 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
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 1:2500 live births
21/04/23 34Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Turner’s Syndrome
21/04/23 35Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Turner’s Syndrome
Webbed neck, unusual fingers, short stature, low neckline are all features of the condition. Heart, hearing and visual problems can also occur
3621/04/23 Mrs Smith: Ch13: Mutations an
Chromosomal Abnormalities
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 1:1000 live male births
21/04/23 37Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Klinefelter’s Syndrome
21/04/23 38Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Klinefelter’s Syndrome
21/04/23 39Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Task: Torrance pg 100 Qu’s 1-3
21/04/23 40Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities
Essay Question Guide to H-Grade essays pg 62
Discuss how genetic abnormalities can result in certain human conditions. (15)
21/04/23 Mrs Smith 41