Genetics of growth and development

Stages and rates of postnatal development

Postnatal period (from Lat. post — after, natus — birth) encompasses the entire human life after coming into the world. Development during this time is guided by the genetic system; however, its rates can vary under the pressure of the external environment:

• Retardation — delayed growth and development occurring under adverse conditions.
• Acceleration — accelerated processes of organism formation under favorable factors.

For an objective assessment of development rates, physicians use anthropometric indicators (from Lat. anthropos — human, metreon — I measure). The main criteria include body length and mass, chest circumference, biological age markers, and the level of neuropsychological development. It is important to remember age-related dynamics: body proportions change unevenly. For instance, a child's head is relatively larger than an adult's, and its growth finishes early, whereas the limbs (arms) reach their final proportions much later.

Growth pathologies: Turner syndrome

Genetic anomalies directly affect physical development. A classic example is Turner syndrome. This is the only viable sex chromosome monosomy in humans, occurring with a frequency of 1:3000.

• Karyotype: 45, X0 (the second sex chromosome is absent).
• Phenotype: Exclusively female sex is formed.
• Clinical picture: The leading symptoms are pronounced growth retardation (short stature), delayed puberty, and underdevelopment of the internal genital organs.

Genetic and anatomical relationship between humans and animals

The patterns of human development are driven by its evolutionary history. Evidence of belonging to taxonomic groups can be traced in anatomy and embryogenesis:

1. Phylum Chordata (Chordata): During embryogenesis, the notochord, the neural tube above it, and pharyngeal gill slits are laid down. The body exhibits bilateral symmetry.
2. Subphylum Vertebrata (Vertebrata): The skull, spine, two pairs of limbs, and five divisions of the brain are formed. The circulatory system is closed (heart on the ventral side), and the skin is multilayered.
3. Class Mammalia (Mammalia): Characterized by warm-bloodedness, a four-chambered heart with a left aortic arch, a diaphragm, 7 cervical vertebrae, and 3 auditory ossicles. Hair, mammary, sweat, and sebaceous glands appear, along with a developed cerebral cortex and viviparity.
4. Subclass Placentalia (Placentalia): Intrauterine development with fetal nutrition via the placenta.
5. Order Primates (Primates): Binocular vision and touch develop (with a weakened sense of smell). Grasping-type limbs with nails, present clavicles, a flat and broad chest, and a reduced tail. What unites us with primates is tooth replacement, 4 blood groups, biochemical similarity (interchangeability of proteins, such as growth hormone), similar gestation periods, and shared diseases (syphilis, cholera, tuberculosis). The difference in the karyotype (humans — 46, great apes — 48) is due to a single chromosome translocation.

Population waves as an evolutionary factor

Population waves ("waves of life") are sharp fluctuations in the number of organisms. The term was introduced by S.S. Chetverikov in 1905. The biological significance of the phenomenon is that during a sharp drop in numbers, the surviving individuals become the founders of a new population, which radically alters allele frequencies (for example, in the Siberian silkworm, fluctuations reach 12 million-fold).

In the human population, agriculture and industry have been growth factors, while epidemics (plague, smallpox, influenza) have been reduction factors. Epidemics acted as a severe selective factor.

Example of the plague's impact on the gene pool: Plague foci in Asia historically coincide with zones of low frequency of the $I^0$ allele and high frequency of the $I^B$ allele. The plague pathogen (Y. pestis) possesses an H-like antigen that is very structurally similar to the $I^0$ (0) blood group antigen. Due to this antigenic similarity, the immune system of people with the first blood group recognized the infection more poorly. As a result, such individuals were less resistant to the disease and were massively eliminated in epidemic foci.

Class and exam questions

What else to study on this topic

• Methods for assessing anthropometric indicators and biological age.
• Age-related dynamics of changes in human body proportions.
• Comparative anatomy and embryogenesis of chordate animals.
• Specific infectious and parasitic diseases of primates and humans.
• Mechanisms of chromosomal translocations in karyotype evolution.

Other topics in the "Additional Topics" section

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