BIOL 2030 Lecture Notes - Lecture 27: Sister Chromatids, Homologous Chromosome, Down Syndrome
Mutations and their Effect on Phenotype
April 1, 2016
Mutation: permanent change in the hereditary material (DNA/RNA)
Mutations can occur in:
• Somatic cells of a multicellular organism
o Occur in non-reproductive cells and are passed to new cells through mitosis,
creating a clone of cells having the mutant gene
o Can arise spontaneously or be induced by a chemical or physical mutagen
o They can be transmitted to daughter cells via mitosis
o They differ from germ-line, which are inherited genetic alterations
o By definition, they are not transmitted by offspring of parents carrying somatic
mutation
o In most cases, a somatic mutation has little or no effect, but some may give rise to
cancer
• Germ-line cells (sperm/egg)
o Occur in cells that generate sex gametes
o Meiosis and sexual reproduction allow germ-line mutations to be passed on to
approximately half of the next generation
o These offspring will then carry their mutation in all of their cells
o Important in variation that leads to speciation
*substantially different consequences
Three Types of Mutation:
1. Chromosomal mutations – affect number or structural aberrations
2. Transposition of genes (via transposable elements)
3. Point mutations – alterations involving one or few changes in the DNA
(substitution/deletion/insertion of 1 or more base pairs)
Chromosomal Rearrangements
• Duplication
• Deletion
• Inversion
• Translocation
Non-Disjunction in Meiosis = gain or loss of chromosomes
• Of homologous chromosomes in meiosis I
• Of sister chromatids in meiosis II
• Ex. Trisomy 21
find more resources at oneclass.com
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Document Summary
Mutation: permanent change in the hereditary material (dna/rna) Three types of mutation: chromosomal mutations affect number or structural aberrations, transposition of genes (via transposable elements, point mutations alterations involving one or few changes in the dna (substitution/deletion/insertion of 1 or more base pairs) Non-disjunction in meiosis = gain or loss of chromosomes: of homologous chromosomes in meiosis i, of sister chromatids in meiosis ii, ex. Insertion/deletion of nucleotides: frameshift mutation may cause immediate nonsense (stop codon, frameshift mutation may cause extensive missense, insertion/deletion of 3 nucleotides: no frameshift but extra/missing amino acid. *amino acid arising will determine effect = due to charged or hydrophobic or polar character: negative negative: effect is small or minuscule, positive negative: dramatic effect. Classifications of mutations: summary: transition vs transversion, silent mutation, missense, neutral, radical leading to loss of function, radial leading to gain of function, nonsense, frameshift missense/nonsense mutation.
