The genome is the set of genetic instructions found in a cell that make biological life possible. In the case of humans, these instructions are stored in 23 pairs of chromosomes (23 maternal chromosomes and 23 paternal chromosomes), being chromosome 23 different regarding gender (XX for women and XY for men).
The picture of those 23 pairs of chromosomes constitutes the human karyotype (female in this case). Any change that alters the karyotype (aneuploidy or chromosomal abnormality) will trigger syndromes. Among these possible changes that the karyotype can suffer we find monosomies and trisomies.
What are aneuploidies?
Aneuploidy is a situation in which there are one or more extra chromosomes or one or more missing chromosomes. Because each chromosome contains hundreds of genes, the addition or loss of a single chromosome upsets the balance in cells and, in most cases, is not compatible with life.
Most chromosomal abnormalities occur during sperm and egg generation. They occur because chromosomes become unbalanced during the process in which gametes are generated (process called meiosis). These abnormal gametes are usually eliminated during spermatogenesis or oogenesis. However, some of these abnormalities can also occur during the beginning of embryo division, affecting the developing embryo.
Types of aneuploidies
In humans, the most common types of aneuploidy are trisomy. About 0.3% of births have this genetic disorder (an extra chromosome). If you want to know more, see our article about trisomies (Down syndrome or trisomy 21, Edwards syndrome or trisomies 18, Patau syndrome or trisomy 13).
Monosomies are the complete absence of one of the chromosomes found in humans. Among them we find Turner syndrome.
Monosomies are usually caused by errors during cell division, either by mutations in genes involved in DNA replication or by chromosomal rearrangements such as deletions, duplications or translocations. The most common monosomy is the deletion of the entire X chromosome (monosomy XO), resulting in Turner syndrome.
Turner syndrome affects women (about 1 in 2,500). It is characterized by the lack of an X chromosome and affects the development of girls. People with this monosomy have as their most characteristic features short stature and infertility.
Women with this syndrome usually have a short neck, ears located lower than normal and swollen hands and feet.
They may also have associated health problems such as high blood pressure, diabetes, kidney problems, osteoporosis, cataracts and thyroid problems.