1. CHROMOSOMAL MUTATIONS BY- DR.(Mrs.) T.S.KHAN (PGT BIOLOGY)

2. Chromosomal Mutations  Deletion – part of the chromosome is missing –Starts with breaks in the chromosome –Radiation, heat, viruses, chemicals, etc. –May cause an unpaired loop –May give rise to pseudodominance –Cri-du-chat syndrome (Chrom. #5)

5. Chromosomal Mutations  Duplication – doubling of a segment of a chromosome –Tandem –Reverse tandem –Terminal tandem –Position Effect of barring eyes in Drosophila

8. Chromosomal Mutations  Inversion – results when a segment of a chromosome is excised and then reintegrated in an orientation 180 degrees from the original orientation. –Pericentric inversion –Paracentric inversion –Resulting from a dicentric bridge

10. Chromosomal Mutations  Translocation – change in position of chromosome segments and the gene sequences they contain to a different location –Nonreciprocal intrachromosomal –Nonreciprocal interchromaosomal –Reciprocal interchromosomal

12. Chromosomal Mutations  Fragile Sites and Fragile X Syndrome –Narrowings or unstained areas (gaps) –Recessive X-linked traits (predominately males) –Normal transmitting males carrying a premutation will have grandsons with mental retardations and some granddaughters (up to 33%) with mild retardation

14. Variation in Chromosomal Number  Euploidy – the correct number of sets of chromosomes in an organism  Monoploidy – only one set of chromosomes when there should be more –Male wasps, ants, and bees are monoploids because they develop from unfertilized eggs –Used in plant-breeding experiments/colchicine (inhibits mitotic spindle)

15. Variation in Chromosomal Number Polyploidy – having three or more sets of chromosomes –Usually occurs due to a breakdown of the mitotic spindle –Usually occurs in plants (self-fertilization) –Even numbered polyploids have a better chance of being fertile than odd numbered polyploids –In humans, triploidy is usually lethal.

16. Variation in Chromosomal Number Polyploidy (continued)  Autopolyploidy –All sets of chromosomes originate in the same species/defect in meiosis –Example – a diploid gamete fuses with a haploid gamete to produce a triploid zygote (bananas and seedless fruit)

17. Variation in Chromosomal Number Polyploidy (continued)  Allopolyploidy –Sets of chromosomes originate from different species though usually related –Because of differences between chromosomes, the hybrid, no crossing over occurs and no viable gametes produced making hybrids sterile –Occasionally, tow sets of different chromosomes will double, producing tissues of 2N + 2N 2 / produces fully fertile allotetraploid, 2N + 2N 2, plants

19. Variation in Chromosomal Number  Aneuploidy – variation in the number of chromosomes –Nullisomy - loss of one homologous chromosome pair; 2N – 2 –Monosomy – loss of a single chromosome; 2N – 1 –Trisomy – single extra chromosome; 2N + 1 –Tetrasomy – extra chromosome pair; 2N + 2

21. Variation in Chromosomal Number  In humans, Down Syndrome is the only disorder where an extra autosomal chromosome exists and the individuals lives past three months. All other embryos will self-abort or the infant will die within 6 months. However, extra sex chromosomes will not cause an embryo to necessarily abort; but the individual may have other distinguishable characteristics.

22. Variation in Chromosomal Number  Trisomy-21 – Down Syndrome  Trisomy-13 (Patau syndrome) – cleft lip and palate, small eyes, polydactyly and mental retardation. Dies within 3 months  Trisomy-18 (Edwards syndrome) – developmental retardation, congenital malformations, and die within 6 months