#A Chromosomal Inheritance and Genetic Alterations

Key vocabulary terms covering gene variants, meiotic recombination, chromosomal structural rearrangements, and numerical chromosome abnormalities.

Alleles

Gene variants that exist at the same relative locations on homologous chromosomes (all options for a trait).

Crossing over

The process where chromosome segments are exchanged between non-sister homologous chromatids.

Duplications and deletions

Chromosomal alterations involving extra genes (duplications) or lost genes (deletions) that often produce offspring that survive but exhibit physical and mental abnormalities.

Inversion

A chromosomal mutation that occurs when a chromosome segment breaks from the chromosome, reverses its orientation, and then reattaches in the original position.

Reciprocal translocation

A chromosomal rearrangement occurring between two nonhomologous chromosomes that does not cause any genetic information to be lost or duplicated.

Monosomy

The loss of one chromosome; autosomal monosomies fail to develop to birth.

Trisomy

The gain of an extraneous chromosome (third copy); most autosomal trisomies fail to develop to birth, though duplications of chromosomes 13, 15, 18, 21, or 22 can result in offspring surviving for several weeks to many years.

Trisomy 21

The most common form of trisomy, which leads to Down's Syndrome.