Gene and chromosomal abnormalities of the embryo/fetus:
• Frequent chromosomal abnormalities:
• monosomy X (45X) - Shereshevsky-Turner syndrome (the absence of one X chromosome in girls);
• trisomy (additional chromosome) (47XXY) – Klinefelter's syndrome (additional female sex chromosome X in male XY karyotype);
• trisomy 13 chromosomes - Patau's syndrome;
• trisomy 16 chromosomes - spontaneous abortion;
• trisomy 18 chromosomes - Edwards syndrome;
• trisomy 21 chromosomes - Down's syndrome.
• Chromosomal rearrangements:
• failure of meiosis in any period of division (meiosis is the process of division of the mother cell with a complete set of chromosomes, in which germ cells (gametes) with a half set of chromosomes are formed);
• failure during fertilization - dyspermia (fertilization by two or more spermatozoa) with the formation of a polyploid embryo;
• failure during the first mitotic divisions of a fertilized egg (mitosis is a process of cell division in which daughter cells have a complete set of chromosomes);
• chromosomal translocations in one of the partners: 1) Reciprocal translocations - two fragments from two different chromosomes break off and change places. 2) Robertsonian translocations - one chromosome connects to another.