Today, when research on deciphering the human genome has already been completed and moved to the practical plane, when diagnostic medicine is able to determine genetic abnormalities in the embryo, for many ordinary people it remains unclear what a karyotype and genome are. In this article, we will define and outline the differences between these two concepts.
Elements 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 features (number, shape and size) of chromosomes that is characteristic of each biological species (species karyotype) and each 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 male is 46,XY or a female is 46,XX. The first digits indicatethe number of paired autosomes (homologous chromosomes), and the letters - on the sex chromosomes, which determine the sex of the 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 deviations in the karyotype are carried by women until the end of pregnancy.
Why is this happening
Disturbances in the karyotype we owe to various kinds of failures 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. During the formation of gametes, a failure 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 divisions of the zygote transmit such a pathology to the cells of the whole organism.
Individual karyotype
What is karyotyping? This is a procedure for isolating and staining an individual's chromosomes for later analysis. Any cell in the body that divides is suitable for this procedure. After all, the spiralization of chromosomes, as we see them in the pictures, occurs at the stage of the metaphase of mitosis (simple cell division).
For human karyotypingbone marrow cells, skin fibroblasts or blood leukocytes can be used. It is blood for the karyotype that is most often used due to 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 stripes, and it is they that give an idea of rearrangements, breaks and deletions (losses) in their structure.
Chromosome Passport
Studies of an individual's karyotype make it possible to establish his genetic status - quantitative and qualitative anomalies of chromosomes. It is violations in the karyotype that are often the cause of varying severity of violations of fertile functions, a child's mental or mental developmental delay, and other pathologies associated with the chromosome set.
The most frequently established violations in the number of chromosomes in the karyotype (aneuploidy and polyploidy). The most well-known anomalies are Down's syndrome (trisomy 21), Edwards syndrome (trisomy 18), Turner's syndrome (monosomy X), and Klinefelter's syndrome in men (trisomy X).
Structural abnormalities of chromosomes (deletions, duplications, translocations, inversions) most often lead to various metabolic pathologies.
What does this give us
We are all carriers of anomalies in the karyotype, while we can be absolutely he althy outwardly. But they can be the cause of infertility, abortion. Moreover, these anomalieskaryotype most often lead to the birth of a child with developmental anomalies in a pair of he althy parents.
Karyotyping a couple who are planning to have a child and have reproductive problems helps genetic consultants assess the chances of having he althy offspring and develop a program to address the problem of infertility or miscarriage.
Separately, it is worth noting the prenatal diagnosis of the karyotype. In this case, the umbilical cord blood of the fetus is taken for analysis and the karyotype is analyzed. In this way, abnormalities in the development of the fetus in the earliest stages of pregnancy can be determined.
Postnatal (after birth) karyotyping is relevant for people who have serious he alth problems. Developmental delays, autism, puberty disorders, infertility or recurrent miscarriages are all reasons to seek medical genetic counseling.
