لخّصلي

Phenocopy non-inherited change of phenotype imitating the mutations, which is provoked by environmental factors. In medicine it is unheritable disease, which has the same clinical picture as monogenic heritable disease. The effect of teratogens on the pregnant woman is at the bottom of this. Teratogens (different chemical or biological substances) disturb embryogenesis, but can't change a fetal genotype.

Example. One type of congenital cataract is heritable. Other type of congenital cataract is provoked by virus of German measles and is unheritable. The clinical pictures of both diseases are nearly identical.

Genocopy appearance of similar phenotypical signs under influence of different genes. They can be placed in different loci of one chromosome or in different chromosomes.

Example. There are two forms of Phenylketonuria (PKU). The reason of first (classical type) is the mutation of enzyme phenylalanine hydroxylase. By this type the phenylalanine is accumulated in blood because of low activity of enzyme. It is treated by low-PhA diet. The reason of second type is mutation of two genes of 6- pyruvoyltetrahydropterin synthase (PTS) caused PTS deficiency. But the activity of enzyme is normal. This type of PKU is untreated by diet.

Task 3. The ground of genealogical method. Home task

The genealogical method is the general and obligatory method of genetic consultation. It permits to resolve the following problems:

1. 
   

   Is the disease heritable or not;

   
   


2. 
   

   The type of inheritance;

   
   


3. 
   

   Determine the genotypes of family's members;

   
   


4. 
   

   Determine, who from family's members are the obligate and facultative heterozygote. 5

   
   

. Calculate the probability of this disease appearance among relations.

The main stages of genealogic analysis are:

1. 
   

   The collection of information (interrogation and inspection) about presence (or absence) the sign (disease), which is analyzed and composition of legend about the relations of proband. It is desirable to collect data about 3-4 generations.

   
   


2. 
   

   The graphical representation of pedigree (the family tree) with indication of relations and the presence of analyzable sign. We can use the system of specific signs to compose the family tree (seeFig * 0.1) . Each generation is marked by Roman numerals, the members of generation are marked by Arabic numerals, and sibs are marked in order of their birth.

   
   


3. 
   

   The analysis of pedigree (the solution of problems).

   
   

Target 1.

Determination of analyzable disease's type (heritable disease, multifactorial

(MFD) or phenocopy).