University:
Kentucky State University
Course:
BIO 307 | Genetics
Academic year:

2024
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447

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17
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teespagmaxrtf

Genetics Lecture title: Mutations Date:29/3/2022 Lecture # 7: Mutations What is DNA mutation ? • A mutation is a change in DNA, the hereditary material of life. ... So a change in an organism's DNA can cause changes in all aspects of its life. • Mutations are essential to evolution; they are the raw material of genetic variation. • Permanent changes in the genome of an organism 4 Lecture # 7: Mutations Classification of mutations Classification of mutations by their effects on phenotype proteins 1. Silent mutation: A change in DNA nucleotides present in either coding or non- coding sequences but it does not lead to change in the functions of phenotypic proteins. 2. Loss of function mutations Mutations that change the functions of important phenotypic proteins. 3.Conditional mutations Mutations that cause temporary change in the phenotypes, related to certain restrictive conditions. For example: change in temperature. 5 6 Lecture # 7: Mutations Classification of mutations • Classification of mutations by their effects on the DNA molecule at the DNA molecular level, mutation can be divided into two major groups. A. Point mutations : A mutation limited to one nucleotide pair in a single gene. 1. base-pair substitutions 2. base-pair insertions or deletions. B. Chromosomal mutations : 1. Abnormal Numbers 2. Abnormal structure 7 Lecture # 7: Mutations Classification of mutations A. Point mutations / 1. Substitutions • The replacement of one base pair with another that occurs when a nucleotide and its partner from the complementary DNA strand are replaced with another pair of nucleotides. • Base-pair substitutions are either missense mutations or nonsense mutations. • Missense mutation = Base-pair substitution that alters an amino acid codon (sense codon) to a new codon that codes for a different amino acid. • e.g. Sickle cell anemia. 8 Sickle cell anemia Missense mutation could be due to transition or transversion base substitution.In transition: the mutation is due to changes from pyrimidine to pyrimidine (CT) or Purine to purine (AG) base pairing. In transversion : the mutation is the result of changes from pyrimidine to purine or purine to pyrimidine base pairing. 9 Lecture # 7: Mutations Classification of mutations A. Point mutations / 1. Substitutions Nonsense mutation = Base-pair substitution that changes an amino acid codon (sense codon) to a chain termination codon, or vice versa. • Nonsense mutations can result in premature termination of translation and the production of abnormal short polypeptide. • Nearly all nonsense mutations lead to nonfunctional proteins. 10 11 Lecture # 7: Mutations Classification of mutations A. Point mutations / 2. Insertions or Deletions • Base-pair insertions or deletions usually have more negative effect on proteins formation than substitutions. • Base-pair insertion = The insertion of one or more nucleotide pairs into a gene. • Base-pair deletion = The deletion of one or more nucleotide pairs from a gene. • Frameshift mutation 12 Lecture # 7: Mutations Classification of mutations A. Point mutations / 2. Insertions or Deletions • This type of frame shift mutation will occur whenever the number of nucleotides inserted or deleted is not 3 or a multiple of 3. • Frame shift mutation = A base-pair insertion or deletion that causes a shift in the reading frame, so that codons beyond the mutation will be the wrong grouping of triplets and will specify the wrong amino acids. • Frame shift will produce a nonfunctional protein unless the insertion or deletion is very near the end of the gene. 13 The non-frameshift effect is lesser than the frameshift effect 14 Lecture # 7: Mutations Classification of mutations B. Chromosomal mutations • Balanced alterations: do not result in a gain or loss of genetic material and usually have fewer clinical consequences • Unbalanced alterations: alterations result in a loss or gain of genetic material 15 Lecture # 7: Mutations Classification of mutations B. Chromosomal mutations Somatic Mutations : Mutations occur in all body cells except those responsible to produce eggs or sperms by meiosis. Somatic mutations may result in unusual cell growth (such as cancer). Germinal Mutations : Mutations in cells responsible to produce gametes (eggs and sperms). Germinal mutations result in genetically altered gametes that may be passed on to the individual's offspring causing their genetic disorders. 16 Lecture # 7: Mutations Classification of mutations B. Chromosomal mutations ‫القطعة‬ ‫االصغر‬ 17 Lecture # 7: Mutations Methylatio of DNA can effect its activity without changing its sequence Chromosome Parts • Heterochromatin: ‫ال تُترجم‬ • More condensed • Silenced genes (methylated) • Gene poor (high AT content) • Stains darker • Euchromatin: • Less condensed • Gene expressing • Gene rich (higher GC content) • Stains lighter 18 Lecture # 7: Mutations Chromosome Parts ‫ امثلة على‬Heterochromatin Telomeres – chromosome tips • Repeats • Act as sort of biological clock • Being whittled down at each Mitosis Centromeres – middle • Highly condensed • Also repetitive sequence • Region where spindle fibers attach • Pulling chromatids apart during Mitosis 19

Mutations Lecture

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