Lecture 11 Flashcards
Metacentric
Centromere is located in the middle of the chromosome
Submetacentric
Centromere is located NEAR the middle of the chromosome, but it favors one side or the other (not directly in the middle)
Acrocentric
Centromere is located near the end of the chromosome
Telocentric
Centromere is located at the end of the chromosome
What is the NOR?
Nucleolar Organizer Region; region around which the nucleolus forms; can be detected by silver staining and is a useful landmark for chromosome identification; contains tandem repeats of genes encoding ribosomal RNA
Steps in Karyotyping
- Chromosomes prepared from actively dividing cells
- Halted in metaphase (with Colchicine)
- Chromosomes arranged according to size
G Banding
Bands with giemsa stain; heterochromatin stains intensely, euchromatin stains lightly; 400-600 bands can be identified in metaphase chromosomes
Q Banding
Bands with quinacrine stain; florescent stain for A/T rich regions
C Banding
Reveals centromeric heterochromatin; constitutive heterochromatin around the centromere is intensely stained
R Banding
Regions rich in cytosine-guanine base pairs; uses reverse giemsa staining; treatment with high temperature, low pH, or acridine orange
T Banding
Telomeric banding after heat denaturation
Aneuploidy
Loss or gain of chromosomes
Polyploidy
Cells or organisms containing more than two complete paired (homologous) sets of chromosomes
Deletions
Loss of a chromosomal segment; large deletions are easily detected; during pairing, normal chromosome loops out
Effects of Deletions
Imbalances in gene product, expression of a normally recessive gene (pseudodominance), and haploinsufficiency
Paracentric Inversion
Inversion in which the breakpoints are confined to one arm of a chromosome; inverted segment does not span the centromere
Pericentric Inversion
Inversion in which the breakpoints occur on both arms of a chromosome; inverted segment spans the centromere
Inversions in Meiosis in Homozygous vs Heterozygous Individuals
Homozygous - no problems arise during meiosis
Heterozygous - homologous sequences align only if the 2 chromosomes form an inversion loop; individuals with para- or peri- centric inversions often have nonfunctional gametes due to loss of large amounts of genetic material during meiosis
Reciprocal Translocation
Exchange of material between homologous chromosomes
Nonreciprocal Translocation
Transfer of genes from one chromosome to another nonhomologous chromosome
Robertsonian Translocation
Rare chromosomal rearrangement that, in humans, generally occur in the 5 acrocentric chromosome pairs 13, 14, 15, 21, and 22; other robertsonian translocations can occur, but do not lead to a viable fetus; frequency is about 1:1000 newborns
