Today, when research on the decoding of the human genome has already been completed and switched to the practical plane, when diagnostic medicine is able to determine genetic abnormalities in the embryo, for many inhabitants it remains unclear what the karyotype and genome are. In this article, we will define and outline the differences between these two concepts.
The basics of molecular biology
What is a genome? This is the entire set of gene material - 22 autosomes and a pair of sex chromosomes in the nucleus and mitochondrial DNA, which, according to the Human Genome project, contain 3.1 billion base pairs (recall adenine, guanine, cytosine and thymine).
What is a karyotype? This is a set of characters (number, shape and size) of chromosomes, which is characteristic of each biological species (species karyotype) and each individual individual (individual karyotype).
Standard and pathology
The karyotype, the norm of which is strictly species-specific, is the main limiter in interspecific crossing. For example, the karyotype of your domestic cat is 38, XY, and the karyotype of a man is 46, XY or a woman is 46, XX. The first numbers indicate the number of paired autosomes (homologous chromosomes), and the letters indicate sex chromosomes that determine the sex of an individual.
As already clear, the karyotype of the biological species Homo sapiens includes 22 pairs of chromosomes that have the same shape and size and 1 pair of sex chromosomes (XY - male, XX - female karyotypes). Any deviations from such a normal karyotype in humans lead to various kinds of developmental disorders and are most often fatal. According to modern statistics, only about 0.5% of fetuses with abnormalities in the karyotype are carried by women before the end of pregnancy.
Why it happens
We owe violations to the karyotype of various kinds of malfunctions in the process of formation of gametes - the egg and sperm. Gametogenesis is a complex process, it is based on a specific form of cell division - meiosis. With the formation of gametes, a malfunction in the distribution of hereditary material may occur, and then the gametes will have an abnormal set of chromosomes, which as a result of their fusion (fertilization) will lead to the formation of a zygote with an abnormal karyotype. Subsequent zygote divisions translate this pathology into cells of the whole organism.
Individual karyotype
What is karyotyping? This is a procedure for isolating and staining an individual's chromosomes for subsequent analysis. For this procedure, any body cells that divide are suitable. Indeed, the spiralization of chromosomes, as we see them in the pictures, occurs at the stage of metaphase mitosis (simple cell division).
For human karyotyping, bone marrow cells, skin fibroblasts or blood leukocytes can be used. It is blood for the karyotype that is most often used because of the ease of obtaining the material.
After staining procedures, all human chromosomes can be identified and analyzed, since each chromosome has its own individual pattern of bands, and they give an idea of the rearrangements, breaks and deletions (losses) in their structure.
Chromosome Passport
Studies of an individual's karyotype make it possible to establish its genetic status — quantitative and qualitative anomalies of chromosomes. It is violations in the karyotype that are often the cause of the varying severity of impaired fertility, child lag in mental or mental development, and other pathologies associated with the chromosome set.
Most often, violations in the number of chromosomes in the karyotype (aneuploidy and polyploidy) are established. The most known anomalies are Down syndrome (trisomy for 21 pairs), Edwards syndrome (trisomy for 18 pairs), Turner syndrome (monosomy on the X chromosome) and Klinefelter syndrome in men (trisomy on the X chromosome).
Structural chromosome abnormalities (deletions, duplications, translocations, inversions) most often lead to various pathologies of metabolism.
What does it give us
All of us are carriers of abnormalities in the karyotype, while we can be absolutely healthy in appearance. But they can be the cause of infertility, abortion. In addition, it is precisely such anomalies of the karyotype that most often lead to the birth of a pair of healthy parents of a child with developmental abnormalities.
Karyotyping a couple who are planning to have a baby and have problems with reproductive function helps genetic counselors to assess the chances of having healthy offspring and develop a program to solve the problem of infertility or miscarriage.
Separately, it is worth noting the prenatal diagnosis of the karyotype. In this case, fetal umbilical cord blood is taken for analysis and the karyotype is analyzed. In this way, abnormalities in the development of the fetus in the very early stages of pregnancy can be determined.
Postnatal (after birth) karyotyping is relevant for people who have serious health problems. Delays in development, autism, impaired puberty, infertility or repeated miscarriages - all this is an occasion to consult a doctor of medical genetic counseling.