At the beginning, an egg is fertilized by sperm. Basically, every human cell contains DNA (Deoxyribonucleic acid) which is a biomolecule that carries genetic information. This molecule consists of two biopolymer strands coiled around each other to form a double helix. DNA is organized into long structures called chromosomes which can be depicted in a standard format known as a karyogram. In humans, each cell nucleus contains a total of 46 chromosomes with one set of 23 chromosomes from each parent, one set from the mother and one from the father. [1]

The 23rd pair of chromosomes is called sex chromosomes which determine the sex of an individual. Females have two copies of the X chromosome, while males have one X chromosome and one Y chromosome. [2]

However, there are exceptions like the Swyer syndrome which is a disorder of the SRY gene on the Y chromosome. Women with Swyer syndrome have an XY chromosomal makeup, that is, they have a female phenotype but lack ovaries. [2]

Next to the XX and XY chromosomal makeup there are other genetic conditions like the XYY syndrome in which the extra Y chromosome has hardly any physiological effects. The Turner syndrome, a condition in which a female is missing an X chromosome is the only known form of monosomy that enables viability, however, at the expense of restricted fertility. Another condition is the Klinefelter syndrome that results from two or more X chromosome in males. Sypmtoms are often of cognitive and physical nature regarding development and performance. [3] [4] [5]

People suffering from these conditions can lead an almost normal life with the help of hormonal therapies. [3]

Further Links:
Nur eine Handvoll Leben, Franziska Meletzky, 2016 (Film-Review)
The Miracle of Life, Silvio Falcinelli (Rendering3D.net), 2012 (YouTube)