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Chapter 13: Mutations and Chromosomal Abnormalities

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

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Chapter 13: Mutations and Chromosomal Abnormalities

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  1. Higher Human Biology Unit 1: Cell Function and Inheritance Chapter 13: Mutations and Chromosomal Abnormalities Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  2. 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 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  3. You need to know these words Klinefelter’s Syndrome Insertion Nucleotide Mutant Deletion Gene Mutation Substitution Chromosomal Abnormality Point mutation Inversion Frequency of mutation Albinism Frameshift Cystic fibrosis Non-disjunction Mutagenic Agents Phenylketonuria Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities Down’s Syndrome Turner’s Syndrome

  4. 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 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  5. 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 • 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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  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).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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  7. Substitution – one base is swapped for another – e.g. U for C Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  8. Inversion • Inversion of two or more nucleotides, i.e. Positions become back to front (inverted)! Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  9. 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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  10. Insertion Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  11. Insertion Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  12. Deletion Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  13. PhenylketonuriaBackground 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). Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  14. 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 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  15. 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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  16. 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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  17. Albinism • Albinism results from a mutation which prevents the formation of enzyme 3 (Melanocyte Tyrosinase). As a result albinos fail to synthesise melanin. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  18. 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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  19. Albinism Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  20. 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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  21. Cystic fibrosis: due to gene mutation • If the info on the gene for the glycoprotein is altered.... Two outcomes..... • 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 • Heterozygous for the mutant allele: they carry the mutant allele masked in their genotype Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  22. Cystic fibrosis Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  23. 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). Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  24. 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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

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

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

  27. Task: Torrance pg 97 Qu’s 1-4 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  28. 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 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  29. 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 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  30. 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. Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  31. Down’s Syndrome (aka 21) Karyotype Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  32. Symptoms of Down’s Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  33. Non-disjunction of Sex Chromosomes If human sex chromosomes are affected by non-disjunction during meiosis then unusual gametes are formed. Normal situation Normal situation Abnormal situation Abnormal situation Spermmother cell. Egg mother cell. 44+ XX 44+ XX 44+ XY 44+ XY Non-disjunction at 1st meiotic division Non-disjunction at 1st meiotic division Normal Meiosis Normal Meiosis 22+ XY 22+ XY 22+ X 22+ X 22+ Y 22+ X 22+ X 22+ XX 22+ XX 22+ X 22+ Y 22+ X 22 22 22 22 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities Normal sperm Normal eggs Abnormal sperm Abnormal eggs

  34. 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 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  35. Turner’s Syndrome Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  36. 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 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  37. 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 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  38. Klinefelter’s Syndrome Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  39. Klinefelter’s Syndrome Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  40. Task: Torrance pg 100 Qu’s 1-3 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

  41. Essay Question Guide to H-Grade essays pg 62 Discuss how genetic abnormalities can result in certain human conditions. (15) Mrs Smith

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