Heterozygous and homozygous organisms

One of the most significant properties of any living organism is the heredity underlying the evolutionary processes on the planet, as well as the conservation of species diversity on it. The smallest unit of heredity is the gene-structural element of the DNA molecule, responsible for the transfer of hereditary information associated with one or another sign of the organism. Depending on the degree of manifestation, dominant and recessive genes are distinguished . A characteristic feature of dominant units is the ability to "suppress" recessive, having a decisive impact on the body, not allowing them to manifest themselves in the first generation. However, it should be noted that, along with full dominance, incomplete is observed, in which the dominant gene is not capable of completely suppressing the manifestation of recessive and overdomainment, involving the manifestation of the corresponding signs in the form stronger than in homozygous organisms. Depending on which alleles (that is, responsible for the development of the same feature), genes he receives from the parental individuals, are allocated heterozygous and homozygous organisms.

Determination of homozygous organism

Homozygous organisms are objects of living nature that have two identical (dominant or recessive) genes by one or another trait. A distinctive feature of the subsequent generations of homozygous individuals is the absence of their splitting of features and their monotony. This is mainly explained by the fact that the genotype of the homozygous organism contains only one type of gametes, indicated by an uppercase letter, in the case of dominant characters, and a lowercase when referring to recessive characters . Heterozygous organisms differ in that they contain different allelic genes, and, accordingly, form two different types of gametes. Homozygous organisms recessive for the main alleles can be designated as aa, bb, aabb, etc. Accordingly, homozygous organisms dominant in alleles have the code AA, BB, AABB.

Patterns of inheritance

The crossing of two heterozygous organisms, whose genotypes can be conditionally designated as Aa (where A is a dominant, a is a recessive gene), makes it possible to obtain, with equal probability, four different combinations of gametes (variant of the genotype) with a 3: 1 splitting by phenotype. By genotype in this case is understood a set of genes that contains a diploid set of a cell; Under the phenotype - a system of external, as well as internal signs of the organism in question.

Dihybrid cross and its features

Consider the patterns associated with the processes of crossing, in which homozygous organisms participate. In the same case, if there is a hybrid or hybrid hybrid, regardless of the nature of the inherited traits, the splitting occurs in a ratio of 3: 1, and this law is valid for any number of them. The cross-breeding of individuals of the second generation in this case forms four main types of phenotypes at a ratio of 9: 3: 3: 1. It should be noted that this law is valid for homologous pairs of chromosomes, the interaction of genes within which is not carried out.