Mutations.docx
Transcript
Karyotyping is the observed characteristics of the chromosomes of an individual or species – to diagnose chromosomal aberrations. Sample is collected. Treat the cells with chemicals to arrest in metaphase. Swelling, separating, and spreading chromosomes using hypotonic solutions. Fix chromosomes to...
Karyotyping is the observed characteristics of the chromosomes of an individual or species – to diagnose chromosomal aberrations. Sample is collected. Treat the cells with chemicals to arrest in metaphase. Swelling, separating, and spreading chromosomes using hypotonic solutions. Fix chromosomes to slide. Stain View and match banding patterns. Arrange by size and location of centromere. Chromosome stains Q-banding Fluorescent stain- stains AT-rich regions G-banding Giemsa stains AT-rich regions- identical to Q binding. R-banding Reverse Giemsa staining of GC-rich regions. C-banding Giemsa stain after DNA denaturation stains regions near the centromeres. Centromere position 4 different types of centromere positions Telocentric= found on end of 2 chromosomes Acrocentric= located close to end of chromosome Submetacentric= not exactly in the centre, has a short arm (P arm) and long arm (Q arm) Metacentric= the centromere is located at the centre of the 2 chromosomes. Ideograms Easier to interpret and modern version of karyotyping. Nomenclature Haploid= single set of chromosomes without homologous pairs Diploid= having 2 homologous copies of each chromosome. Euploidy= having a multiple of the normal haploid number e.g. 46, 69. Aneuploidy= presence of abnormal number of chromosomes. Aneuploidy and Polyploidy are both types of chromosomal abnormalities. Polyploidy Triploidy One complete extra set of chromosomes. Usually caused when more than 1 sperm fertilises an egg. Tetraploidy Failure of first zygotic division. Can be lethal to embryo. Aneuploidy Nullisomy Complete loss of chromosomal pair Monosomy When one of the chromosome pair is missing. Lethal in very early embryogenesis. Trisomy Addition of extra copy of one chromosome. Most are lethal. Examples of different genetic conditions Turner syndrome= presence of 1 X chromosome instead of 2 XX. Spectral karyotyping is a method which is automated therefore takes less time to perform. FISH is a process by which rapid Aneuploidy is screened. This can be done in an embryo before implantation. Performed on cells at interphase. Single base substitutions- missense mutations A new nucleotide alters the codon to produce an altered amino acid in the protein product. e.g. sickle cell anaemia. Glutamate has been substituted for valine. Single base substitutions- nonsense mutations A new nucleotide changes a codon to the one of the stop codons. Means the mRNA will stop prematurely. Indels Indels involving one or two base pairs (or multiples) can have devastating consequences because they cause frameshift mutations. Insertions and deletions Base pairs maybe inserted or removed from DNA sequence. Causes frameshift mutations. Frameshifts often create new stop codons, resulting in a nonsense mutation.
