Lecture 3

Karyotype

A technique to arrest cells in metaphase, stain, and visualize whole chromosomes and haploid genomes under a microscope, with a resolution of 10^8 to 10^9 base pairs.

Fluorescence in situ hybridization (FISH)

A technique useful for analyzing submicroscopic regions using a probe, with a resolution of 10^4 to 10^5 base pairs.

Microarray

A tool that can represent an entire genome by hybridizing patient and reference DNA, indicating chromosomal gain or loss through color, but does not provide information on change location or arrangement.

Whole Genome Analysis

Provides information about aneuploidy, duplications, deletions, single base pair changes, translocations, and inversions; not useful for identifying mutations in a single gene due to interpretation difficulty; offers the highest resolution.

Aneuploidy

Errors in chromosome number usually resulting from meiotic nondisjunction, leading to conditions like trisomy or monosomy, which can cause spontaneous abortion and developmental abnormalities.

Balanced rearrangements

Do not change relative gene dosage; includes many inversions and translocations.

Unbalanced rearrangements

Too many or too few copies of some genes; most deleterious.

Robertsonian translocation

The most common structural chromosome abnormality in humans, occurring in 1/1000 live births, involving 2 acrocentric chromosomes; carriers typically have a normal phenotype but may experience a high rate of miscarriages, difficulty conceiving, or stillbirths.

Balanced rearrangement offspring

Can lead to the production of aneuploid gametes due to improper alignment during meiosis, forming a quadrivalent; they have a chance to create normal offspring but a higher chance of producing unbalanced gametes, leading to abortion.

Chromosome abnormalities

Often alter relative gene dosage, occur in 1% of live births, 2% of pregnancies in women over 35, and cause 50% of spontaneous abortions in women.

Interstitial deletion

A deletion in the middle of a chromosome.

Terminal deletion

A deletion of the end of a chromosome.

Isochromosome

When the arms of the chromosome are mirror images of each other.

Paracentric Inversion

An inversion in a chromosome where the centromere does not lie within the inverted segment.

Pericentric Inversion

An inversion in a chromosome where the centromere lies within the inverted segment.