The process of individual development is sometimes accompanied by failures in the implementation of the ontogenesis program, provoked by disorders of

Developmental abnormality [Genetic homeostasis deviations, disorders, anomalies]

The process of individual development is sometimes accompanied by failures in the implementation of the ontogenesis program, provoked by disorders of genetic apparatus or by negative impact from the outside. As a result, different kinds of deviations may appear — developmental abnormalities. This is not only significant deviations from the normal phenotype, but also various metabolic disorders, leading to malfunctions of the organism. For the development of the embryo first 12 weeks are especially dangerous — a period when there is formation of organs.

Developmental homeostasis

The individual development of each species has a clear program defined genetically. Only the organisms who realized it have a chance to be born healthy and strong, to grow, to mature, and leave many descendants. The property of organisms to maintain a program of ontogenesis with a minimum number of errors is called developmental homeostasis (from Greek “gomios” — “the same” and “stasis” — “a condition”).

Phenotypic deviations

However, despite the existence of special mechanisms of ontogenesis stabilization, out of seemingly normal zygotes quite often develop defective organisms. What is the reason?

First of all, it is due to various genetic abnormalities in the maternal or paternal gametes caused by mutations on chromosome level or of individual genes. Upon chromosomal rearrangements, the mitotic cell division in the developing organism lasts, for example, longer than usual. This leads to organs origin violations and, ultimately, to the maldevelopment of the body or its parts. If these are point mutations, so occurs a violation of the synthesis of certain structural proteins or enzymes. In the latter case, one of the thousands of interrelated chemical reactions doesn’t occur in cells at all or not fast enough. As a consequence — the accumulation of unwanted substances in the cells, poisoning them and the whole body, and slowing metabolism and individual development. In any case, failures in embryo metabolism lead to various kinds of violations of ontogenesis, which can manifest itself externally in the form of apparent deviations of the normal phenotype — phenotypic deviations, or phenodeviations (diagram 103), or internally — physiologically. In humans, it is most often expressed in mental retardation. Taken from http://worldofschool.org

Diagram 103. A variety of developmental abnormalities (phenotypic deviations) in animals

Reasons for developmental abnormalities

The reason for deviations in individual development may be the so-called environmental stress — various potent external factors on the body. These include not only the physical impact on the developing organism (a sudden change in temperature where the embryo develops; ionizing radiation; lack of oxygen), but also chemical agents. And a great danger for the people is not only in toxic substances, currently abundant in the environment and passively entering the body, but in medications that a woman uses during pregnancy. Of particular danger to the developing organism are various viral and bacterial infections.

Abnormal morphogenesis

Abnormal morphogenesis can be caused not only by environmental pollution, viral and bacterial infections, but even infection by larvae of parasitic worms. For example, tadpoles, whose metamorphosis took place in urban ponds, often origins, not two, but four or even more pairs of limbs. Multilegged frogs — is quite a normal occurrence for megalopolises’ ponds.

However, until now it is not clear what caused their mass appearance: because of not very pure water with an admixture of gasoline or by infestations of flukes’ larvae, penetrating in those places of tadpoles’ body, where limbs formation occurs.

Questions:
  • How do deviations of the genetic apparatus lead to maldevelopment?