Chromosomes are organized structures of DNA that are found in cells. A chromosome is a singular piece of DNA, which contains many genes and other nucleotide sequences. Chromosomes contain genes that are a single characteristic or piece of information. Human cells have 23 pairs of chromosomes, (22 pairs of autosomes and one pair of sex chromosomes) giving a total of 46 per cell.
Chromosomal defects are surprisingly frequent events. About 20% of all human conceptions have them. It is likely that as many as 1 in 118 newborn infants inherit such an abnormality. Many, if not most, irregular chromosomes are the result of a failure of meiosis in the production of sperm and ova. As many as half of all spontaneous miscarriages may result from gross chromosomal errors. The vast majority of chromosomal abnormalities are so severe as to cause spontaneous abortions early in pregnancies.
There are two major categories of chromosomal abnormalities:
| 1. | irregular number of chromosomes |
|---|---|
| 2. | structural modification in a chromosome |
An inversion is a structural modification in a chromosome in which a segment of a chromosome is reversed end to end. An inversion occurs when a single chromosome undergoes breakage and rearrangement within itself. Inversions are of two types: paracentric and pericentric. Paracentric inversions do not include the centromere and both breaks occur in one arm of the chromosome. Pericentric (which is what I have) inversions include the centromere and there is a break point in each arm. An inversion does not involve a loss of genetic information, but simply rearrange the gene sequence.
Inversions usually do not cause any abnormalities in carriers as long as the rearrangement is balanced with no extra or missing genetic information. However, in people who carry balanced inversions, there is an increased production of abnormal chromatids (this occurs when crossing-over occurs within the span of the inversion). This leads to lowered fertility due to production of unbalanced gametes (i.e. my eggs). 
What this means to me: I have < 25% chance of having eggs with the normal chromosome complement on 7 OR a balanced form of the inversion (what I carry) due to the sheer size of my inversion. The big trick is to get M's sperm to find one of my egg's that carries the normal chromosome 7. If my offspring carry a balanced form of the inversion like I do, they will have problems with fertility later in life as I do. I have been told if I have an egg with an unbalanced chromosome 7 (additional or deleted material), that the pregnancy won't survive past the first trimester as the unbalanced products are incompatible with life in my specific case.
