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.

Mitosis vs. Meiosis

Mitosis	Meiosis
in all tissues (somatic cells) produces diploid somatic cells 1 replication / cell division short prophase (1 hr) no pairing of homologs no recombination daughter cells are identical found in primordial germ cells	Only in testes and ovaries Produces haploids 1 replication / 2 cell divisions long prophase (50+ yrs) pairing of homologs in M1 recombination (prophase) daughter cells different limited to primaryspermatocytes and primaryoocytes

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)

Extract lymphocytes + culture medium + PHA (stimulates cell to enter G1, stimulates growth) Þ incubate 70 hrs, add colcimide (breaks down spindle apparatus, blocks division) Þ centrifuge/resuspend/centrifuge/resuspend Þ stain.

Chromosome Structure

Chromosome Banding and FISH

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.

Gene localization

Identification and characterization of structural chromosome abnormalities

Genetic Applications

Prenatal diagnosis

Infertility

Gene mapping

Recurrent miscarriages or still births

Abnormalities of sexual differentiation and development

Neoplastic Conditions