All the characteristic features of our body are manifested under the influence of genes. Sometimes only one gene is responsible for this, but most often it happens that several units of heredity are responsible for the manifestation of a particular trait at once.
It has already been scientifically proven that for a person the manifestation of such signs as the color of skin, hair, eyes, the degree of mental development depends on the activity of many genes at once. This inheritance does not follow the laws of Mendel exactly, but goes far beyond it.
The study of human genetics is not only interesting, but also important in terms of understanding the inheritance of various hereditary diseases. Now it is becoming quite relevant to turn young couples to genetic consultations so that, after analyzing the pedigree of each spouse, one could confidently say that the child will be born he althy.
Types of inheritance of traits in humans
If you know how this or that trait is inherited, you can predict the probability of its manifestation in offspring. All signs in the body can be divided into dominant andrecessive. The interaction between them is not so simple, and sometimes it is not enough to know which one belongs to which category.
Now in the scientific world there are the following types of inheritance in humans:
- Monogenic inheritance.
- Polygenic.
- Unconventional.
These types of inheritance are further subdivided into several varieties.
Monogenic inheritance is based on Mendel's first and second laws. The polygenic is based on the third law. This implies the inheritance of several genes, most often non-allelic.
Unconventional inheritance does not obey the laws of heredity and is carried out according to its own rules, unknown to anyone.
Monogenic inheritance
This kind of inheritance of traits in humans obeys Mendeleev's laws. Given the fact that there are two alleles of each gene in the genotype, the interaction between the female and male genome is considered separately for each pair.
Based on this, the following types of inheritance are distinguished:
- Autosomal dominant.
- Autosomal recessive.
- X-linked dominant inheritance.
- X-linked recessive.
- Holandric inheritance.
Each type of inheritance has its own characteristics and characteristics.
Signs of autosomal dominant inheritance
The type of inheritance is autosomal dominant - this is the inheritance of predominant traits,which are located on autosomes. Their phenotypic manifestations can be very different. For some, the symptom may be subtle, or it may be too intense.
The type of inheritance is autosomal dominant has the following features:
- The sick trait shows up in every generation.
- The number of sick and he althy people is approximately the same, their ratio is 1:1.
- If children of sick parents are born he althy, then their children will be he althy.
- The disease affects both boys and girls equally.
- The disease is equally transmitted from men and women.
- The stronger the effect on reproductive functions, the greater the likelihood of various mutations.
- If both parents are sick, then the child, being born homozygous for this trait, is more seriously ill than a heterozygote.
All these signs are realized only under the condition of complete dominance. In this case, only the presence of one dominant gene will be sufficient for the manifestation of a trait. An autosomal dominant pattern of inheritance can be seen in humans with freckles, curly hair, brown eyes, and many others.
Autosomal dominant traits
Most of the individuals who are carriers of an autosomal dominant pathological trait are heterozygotes for it. Numerous studies confirm that homozygotes for a dominant anomaly have more severe and severe manifestations compared to heterozygotes.
This typeinheritance in humans is characteristic not only for pathological signs, but also some quite normal ones are inherited in this way.
Among the normal traits with this type of inheritance are:
- Curly hair.
- Dark eyes.
- Straight nose.
- Hump on the bridge of the nose.
- Early male pattern baldness
- Right-handed.
- The ability to roll your tongue.
- Dimple on chin.
Among the anomalies that have an autosomal dominant type of inheritance, the following are best known:
- Multi-fingered, can be both on hands and feet.
- Fusion of the tissues of the phalanges of the fingers.
- Brachydactyly.
- Marfan syndrome.
- Myopia.
If the dominance is incomplete, then the manifestation of the trait can not be observed in every generation.
Autosomal recessive inheritance pattern
A sign can appear with this type of inheritance only in the case of the formation of a homozygote for this pathology. These diseases are more severe because both alleles of the same gene are defective.
The likelihood of such symptoms increases with closely related marriages, so in many countries it is forbidden to enter into a union between relatives.
The main criteria for such inheritance include the following:
- If both parents are he althy but carry the abnormal gene, the child will be sick.
- The gender of the unborn child does not play withno role inheritance.
- One married couple has a 25% risk of having a second child with the same pathology.
- If you look at the pedigree, there is a horizontal distribution of patients.
- If both parents are sick, then all children will be born with the same pathology.
- If one parent is sick and the other is a carrier of such a gene, then the probability of having a sick child is 50%
Many metabolic diseases are inherited by this type.
X-linked type of inheritance
This inheritance can be either dominant or recessive. The signs of dominant inheritance include the following:
- May affect both sexes, but women are 2 times more likely.
- If a father is sick, he can only pass on the diseased gene to his daughters, because the sons receive the Y chromosome from him.
- A sick mother is equally likely to reward children of both sexes with such a disease.
- The disease is more severe in men because they lack a second X chromosome.
If there is a recessive gene on the X chromosome, then inheritance has the following features:
- Sick child can be born to phenotypically he althy parents.
- Most often men get sick, and women are carriers of the diseased gene.
- If the father is sick, then you don't have to worry about the he alth of your sons, they cannot get a defective gene from him.
- The probability of having a sick child in a female carrier is 25%, if we are talking about boys, then it rises to 50%.
This is how diseases such as hemophilia, color blindness, muscular dystrophy, Kallmann's syndrome and some others are inherited.
Autosomal dominant diseases
For the manifestation of such diseases, the presence of one defective gene is sufficient, if it is dominant. Autosomal dominant diseases share some characteristics:
- Currently, there are about 4,000 such diseases.
- Both sexes are equally affected.
- Phenotypic demorphism is clearly manifested.
- If there is a mutation of the dominant gene in the gametes, then it will certainly appear in the first generation. It has already been proven that as men age, the risk of getting such mutations increases, which means that they can reward their children with such diseases.
- Disease often manifests itself in all generations.
Inheritance of a defective autosomal dominant disease gene has nothing to do with the sex of the child and the degree of development of this disease in the parent.
Autosomal dominant diseases include:
- Marfan syndrome.
- Huntington's disease.
- Neurofibromatosis.
- Tubular sclerosis.
- Polycystic kidney disease and many more.
All these diseases can manifest themselves to varying degrees in different patients.
Marfan Syndrome
It's a diseasecharacterized by damage to the connective tissue, and consequently, its functioning. Disproportionately long limbs with thin fingers suggest Marfan's syndrome. The inheritance pattern of this disease is autosomal dominant.
The following signs of this syndrome can be listed:
- Slim body.
- Long spider fingers.
- Defects of the cardiovascular system.
- The appearance of stretch marks on the skin for no apparent reason.
- Some patients report muscle and bone pain.
- Early development of osteoarthritis.
- Curvature of the spine.
- Too flexible joints.
- Speech impairment possible.
- Impaired vision.
You can call the symptoms of this disease for a long time, but most of them are associated with the skeletal system. The final diagnosis will be made after all examinations have been completed and characteristic signs have been found in at least three organ systems.
It can be noted that for some, the signs of the disease do not appear in childhood, but become apparent somewhat later.
Even now, when the level of medicine is high enough, it is impossible to completely cure Marfan's syndrome. Using modern drugs and treatment technologies, it is possible to prolong the life of patients with such a deviation and improve its quality.
The most important aspect of treatment is the prevention of aortic aneurysm. Regular consultations with a cardiologist are required. In case of emergencyshowing aortic transplant operations.
Huntington's Chorea
This disease also has an autosomal dominant inheritance pattern. Begins to appear from the age of 35-50 years. This is due to the progressive death of neurons. Clinically, the following signs can be identified:
- Random movements combined with reduced tone.
- Asocial behavior.
- Apathy and irritability.
- Manifestation of the schizophrenic type.
- Mood swings.
Treatment is only directed at eliminating or reducing symptoms. Tranquilizers, neuroleptics are used. No treatment can stop the development of the disease, so death occurs approximately 15-17 years after the onset of the first symptoms.
Polygenic inheritance
Many traits and diseases are inherited in an autosomal dominant manner. What it is is already clear, but in most cases it is not so simple. Very often, not one, but several genes are inherited at the same time. They appear in specific environmental conditions.
A distinctive feature of this inheritance is the ability to enhance the individual action of each gene. The main features of such inheritance include the following:
- The more severe the disease, the greater the risk of developing this disease in relatives.
- Many multifactorial traits affect a specific gender.
- The more relatives have this trait, thehigher risk of this disease in future offspring.
All considered types of inheritance are classical variants, but, unfortunately, many signs and diseases cannot be explained because they belong to non-traditional inheritance.
When planning the birth of a baby, do not neglect visiting a genetic consultation. A competent specialist will help you understand your pedigree and assess the risk of having a child with abnormalities.
