Đột biến NST

Chapter Chromosomal Variation - Chromosomal mutations can arise in any cell of any tissue Remember that in order to be passed on (inheritied) the mutation must be in germinal tissue - The result of changes in chromosomal structure is a heterogeneous karyotype one normal, one rearranged - Types of mutations: > Deletion > Duplication > Inversion > Translocation - Changes due to: “breaking” and rejoining “illegitimate” recombination Deletions: Interstitial deletiondeletion result of two breaks Terminal deletion*deletion* result of single break A Intragenic deletiondeletion small deletion within gene B Multigenic deletiondeletion large deletion involving two to several thousand genes Recognized by: Reduced recombination frequency Pseudodominance Recessive lethality Lack of reverse mutation visible deletions Pseudodominance - the sudden appearance of a recessive phenotype in a pedigree, owing to a deletion of a masking dominant gene Pseudodominance can be used to deletion map map Higher order duplications Bar Flies! ☺ Inversions: generally viable and usually show no particular abnormalities A break within a gene can result in lethal or other abnormal phenotypes Paracentric inversion - centromere is outside inversion Pericentric inversion - inversion spanning the centromere Dicentric bridge - homologous centromeres are connected Acentric fragment - fragment without a centromere Diagnostic Features: Reduction of recombination frequency Reduced fertility due to unbalanced or deleted meiotic products Directly observed inverted chromosomal landmarks Presence of inversion loops Polyploidy: autopolyploidy - chromosome sets from same species allopolyploidy - or more chromosome sets from related, but distinct species amphidiploid - organism produced by chromosomal doubling (usually in allopolyploid) Autopolyploidy: Effect of genome doubling: It is presumed that the amount of gene product doubles as the genome does Plants tolerate this! Allopolyploid: 1928 G Karpechenko Wanted to make a hybrid that had the leaves of a cabbage and the root of a radish… He got the opposite but did create a fertile plant by spontaneous doubling Somatic allopolyploids from cell hybridization: Plus other manipulations… Modern innovative method of plant breeding… enzymatically digest cell wall stripped cell is called protoplast cell suspensions are combined with polyethylene glycol - fusion occurs fused cells proliferate on agar plates colonies are called calluses Amphidiploidy: A productive natural occurrence important in speciation Amphidiploidy: Triticale Wheat x Rye Wheat: success as a hexaploid is ensured by an allele called, Ph It was inherited from the B set and is located on the long arm of Ch This allele suppresses homeologous pairing Therefore diploid-like behavior ensues Aneuploidy: Somatic aneuploids: arise spontaneously in somatic cells… and result in mosaicism Gynandromorph: