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Mutations and Chromosomal Abnormalities

Mutations and Chromosomal Abnormalities. Mutations. A mutation is a change in the structure or amount an organism’s DNA. This can be a tiny change where only one base is altered or a change in the number of chromosomes.

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Mutations and Chromosomal Abnormalities

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  1. Mutations and Chromosomal Abnormalities

  2. Mutations • A mutation is a change in the structure or amount an organism’s DNA. • This can be a tiny change where only one base is altered or a change in the number of chromosomes. • An individual is called a mutant if a change in the genotype is expressed in the phenotype

  3. Gene Mutations • PKU, Albinism and Cystic Fibrosis are all examples of gene mutations. • One or more of the nucleotides is altered causing a change in the sequence of bases which can affect the amino acids/protein made. • There are point mutations which bring about minor changes and frameshift mutations which lead to a major change.

  4. Point Mutations SUSBSTITUTION OF A NUCLEOTIDE G G C C T C C T C G G C C A C C T C C C G G A G G A G C C G G U G G A G PRO – GLU - GLU PRO – VAL - GLU INVERSION OF TWO OR MORE NUCLEOTIDES A G A G T C T T C A G A T G C T T C U C U C A G A A G U C U A C G A A G SER –GLUN - LYS SER – THR - LYS

  5. Frameshift Mutations INSERTION OF A NUCLEOTIDE G G C C T C C T C G G C C C T C C T C C G G A G G A G C C G G G A G G A PRO – GLU - GLU PRO – GLY - GLY T deleted DELETION OF A NUCLEOTIDE A G A G T C T T C A G A G C T T C G U C U C A G A A G U C U C G A A G C SER –GLUN - LYS SER – ALA - SER

  6. Mutations arise spontaneously and at random but only occur rarely. • The mutation rate can be increased by mutagenic agents such as X-rays, UV light.

  7. Chromosomal Abnormalities • Chromosomes can be affected by mutations where unusual gametes are formed. • Zygotes with abnormal chromosome complements such as 47 chromosomes can be produced due to NON-DISJUNCTION during meiosis.

  8. Non-Disjunction • Homologous chromosomes fail to separate because a spindle fibre fails. • This results in extra or missing chromosomes in the gametes.

  9. Non-Disjunction

  10. Extra copy of chromosome 21

  11. Extra X chromosome causing infertility

  12. Lacks a second sex chromosome causing infertility

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