2 MutationDefinition :, (genetics) any event that changes genetic structure; any alteration in the inherited nucleic acid (DNA) sequence of the genotype of an organism that can alter the amino acid sequence of the protein encoded by the gene .- Mutations are caused by radiation ,viruses and mutagenic chemicals, as well as errors that occur during : meiosis or DNA replication .- Variations can be caused by mutation.Mutations causing variation can arise in 2 ways :1- Numerical abnormalities in chromosomes2- Structural abnormalities in chromosomes
3 A- Numerical abnormalities in chromosomes ( Aneu-ploidy) Definition : This occurs when individual is missing either a chromosome from a pair( monosomy) or has more than two chromosome of a pair( Trisomy , Tetrasomy ) .Example:1- Monosomy : ( 45 chromosome)Turner Syndrome : have only one sex chromosome (X) and affects in female ( growth – shorter than normal - sexual development -ovaries fail ) .2- Trisomy :1-Klinefelter Syndrome :( 47 chromosome)have one extra sex X chromosome (XXY) and affects in male( hypogonadism and sterility)2 - Down Syndrome : (Trisomy 21)have 3 copies of chromosome 21 ,Disorder: (Mongolism – week in the bone and muscles – Bore in heart – heavy tongue )
5 B- Structural abnormalities in chromosomes Type of :1- Mitotic stopping ( C – metaphase )Cause : using carcinogenic material ( Cholchisene ) that cause DNA duplicating without dividing in the cell because of the inhibition in the formation of spindles in metaphaseResult : stopping dividing and chromosomal high coiling without facing the poles .2-Ring Chromosome : that happen in 2 ways1- Cause : when the end of the short and long arms breaksResult : The 2 end stick to each other , thus resulting in loss of information2- Cause : when the 2 ends of the short and long arms stick together usually without loss of materialResult : That ring can cause problems when the cell divides and can cause problems for the individual .
6 3- chromosome fragments Cause : Separation of pieces from the main chromosome .Result : these pieces remind independent without engagement with another chromosome and it lost because it does not has a centromer .4- Bridges ( Di-centric chromosomes)Cause : Physical breakage of the DNA molecule in sister chromatid which produce “sticky ends” before replicationResult : make a bridge between the 2 chromosomal sets in anaphase .6- Sticky chromosomeschromosome are overlapping , unclear and sticky .
7 6- Tri-polesCause : Partial suppression in spindle formation activity .Result : pulled in different ways in anaphase .7- Multi-nucleatedCause : Failure in the formation of the central plate .Result : the cell appear with two or more nuclei .