Chromosomal abnormalities and syndromes

Modifier Genes:

Genes that alter or influence the expression (severity or type) of another genesphenotype. They dont cause a disorder by themselves but can change how a primary mutation is expressed.

Nondisjunction:

The failure of chromosomes to separate properly during cell division (meiosis or mitosis). This error results in gametes or cells with too many or too few chromosomes

Aneuploidy:

An abnormal number of chromosomes.

Trisomy:

A condition where theres an extra copy of a chromosome (e.g., trisomy 21 in Down syndrome).

Monosomy:

A condition where a chromosome is missing from the usual pair.

Robertsonian Translocation:

A rearrangement where the long arms of two acrocentric chromosomes fuse near the centromere and the short arms are often lost. This can lead to balanced carriers or aneuploid offspring.

Isochromosome:

A chromosome that has split incorrectly at the centromere, resulting in two identical arms one arm is duplicated while the other is missing.

VNTRs:

Short sequences of DNA repeated in tandem (one after the other). The number of repeats varies among individuals, contributing to genetic diversity and sometimes being used in genetic fingerprinting.

Deletions

Loss of a segment of a chromosome.

Inversions

A segment of the chromosome is reversed end to end.

Insertions

Extra genetic material is inserted into a chromosome.

Haploinsufficiency:

Occurs when one functional copy of a gene isnt enough to produce a normal phenotype. Loss or inactivation of one allele leads to an insufficient amount of gene product, potentially resulting in disease.

Crossing-Over:

The exchange of genetic material between homologous chromosomes during meiosis. This process increases genetic diversity by producing new combinations of alleles.

Recombinant Chromosomes:

Chromosomes that have undergone crossing-over, carrying a mix of alleles from each parent.

Prader-Willi Syndrome:

An imprinting disorder where genes normally expressed from the paternal chromosome 15 are missing or inactive, leading to a characteristic set of developmental and behavioral problems.

Angelman Syndrome:

An imprinting disorder resulting from loss of gene expression on the maternal chromosome 15 in the same region, causing severe developmental delays, speech impairment, and other neurological issues.