Chromosome Structure and Analysis
Cell Division: Meiosis and Mitosis
Mitosis – produces genetically identical daughter cells.
Meiosis – results in genetically diverse gametes, each with a haploid chromosome compliment.
M2: similar mitotic division.
Potential for generating genetic diversity: maternal and paternal chromosome, recombination.
- M1: reduction division (diploid
Mitosis vs. Meiosis
in all tissues (somatic cells)
produces diploid somatic cells
1 replication / cell division
short prophase (1 hr)
no pairing of homologs
daughter cells are identical
found in primordial germ cells
Only in testes and ovaries
1 replication / 2 cell divisions
long prophase (50+ yrs)
pairing of homologs in M1
daughter cells different
limited to primary spermatocytes and primary oocytes
- Mitosis increases and replenishes cell number with preservation of genetic identity.
- Meiosis spans gap between generations by generating haploid gametes with genetic diversity.
Standard Human Karyotype and Cell Cycle
Karyotype: orderly arrangement of all the chromosomes by their morphology and size.
Lymphocyte Cultures (used for chromosome analysis)
Þ incubate 70 hrs, add colcimide (breaks down spindle apparatus, blocks division) Þ centrifuge/resuspend/centrifuge/resuspend Þ stain.
- Extract lymphocytes + culture medium + PHA (stimulates cell to enter G1, stimulates growth)
Chromosome Banding and FISH
Banding: get patterns on chromosome Þ easier to group or differentiate
G banding = most popular - basic
Q banding = fluorescent technique
R banding = reverse banding (opposite of G)
C banding = darkly stains the centromeres
NOR staining = silver staining in acrocentric chromosomes
FISH (fluorescent In Situ Hybridization)
Labeled DNA probe hybridized to meta or interphase cytogenetics preps.
Identification and characterization of structural chromosome abnormalities
Recurrent miscarriages or still births
Abnormalities of sexual differentiation and development