How to solve problems in genetics on biology?

The study of the basic laws of heredity and the variability of organisms is one of the most complex, but very promising tasks facing modern natural science. In this article we will consider both the basic theoretical concepts and postulates of science, and we will understand how to solve problems in genetics.

The urgency of studying the laws of heredity

Two of the most important branches of modern science - medicine and breeding - are developing thanks to the research of genetic scientists. The very same biological discipline, the name of which was proposed in 1906 by the English scientist U. Betson, is not so much theoretical as practical. Anyone who decides to seriously understand the mechanism of inheritance of various traits (for example, such as the color of eyes, hair, blood type), one must first study the laws of heredity and variability, and also find out how to solve problems in human genetics. This is exactly what we are going to do.

Basic concepts and terms

Each branch has a specific, only inherent, set of basic definitions. If we are talking about the science that studies the processes of transmission of hereditary traits, the latter will be understood as the following terms: gene, genotype, phenotype, parent individuals, hybrids, gametes, and so on. We will meet each of them when we study the rules that explain how to solve biology problems in genetics. But in the beginning we will study the hybridologic method. After all, it is he who underlies genetic research. It was proposed by the Czech naturalist G. Mendel in the 19th century.

How are the signs inherited?

The patterns of transfer of the properties of the organism were discovered by Mendel, thanks to the experiments he conducted with the widely known plant - pea inoculum. The hybrid method is a crossing of two units, which differ from each other by one pair of characteristics (mono-hybrid crosses). If the experiment involves organisms that have several pairs of alternative (opposite) traits, then they speak of polyhybrid interbreeding. The scientist suggested the following form of recording the course of hybridization of two pea plants that differ in the color of the seeds. A - yellow paint, and - green.

In this record F1 - hybrids of the first (I) generation. They are all absolutely uniform (identical), since they contain the dominant gene A, which controls the yellow color of the seeds. The above entry corresponds to the first Mendelian law (the F1 hybridity uniformity rule). Knowledge of it explains to students how to solve problems in genetics. Grade 9 has a program in biology, in which a hybridological method of genetic research is studied in detail. It also considers the second (ІІ) rule of Mendel, called the law of splitting. According to him, the F2 hybrids obtained from the hybridization of the two hybrids of the first generation with each other show a splitting in the phenotypic ratio of 3 to 1, and in the genotype 1 to 2 and to 1.

Using the above formulas, you will understand how to solve problems in genetics without errors, if under their circumstances you can apply the first or already known II Mendelian law, considering that crossing occurs with complete dominance of one of the genes.

The law of independent combination of states of features

If the parents differ in two pairs of alternative characteristics, for example, the coloring of seeds and their form, in plants such as peas, then in the course of genetic crossing it is necessary to use the Pinnet lattice.

Absolutely all hybrids, which are the first generation, obey the Mendelian uniformity rule. That is, they are yellow, with a smooth surface. Continuing to cross each other plants from F1, we get hybrids of the second generation. To find out how to solve problems in genetics, the 10th grade in biology classes uses the record of dihybrid cross, using the phenotype 9: 3: 3: 1 splitting formula. Provided that the genes are located in different pairs, you can use the third postulate of Mendel - the law of independent combinations of states of characteristics.

How are blood groups inherited?

The mechanism of transmission of such a trait as the blood group in humans does not correspond to the laws we examined earlier. That is, he does not obey the first and second laws of Mendel. This is explained by the fact that such a sign as the blood group, according to the studies of Landsteiner, is controlled by three alleles of gene I: A, B and 0. Accordingly, the genotypes will be:

• The first group is 00.
• The second is AA or A0.
• The third group is BB or B0.
• The fourth is AB.

Gene 0 is a recessive allele to genes A and B. And the fourth group is the result of codomination (the mutual presence of genes A and B). It is this rule that must be taken into account in order to know how to solve genetics tasks on blood groups. But that is not all. To establish the genotypes of children by blood group, born from parents with different groups, we use the table below.

The theory of Morgan's heredity

Let's return to the section of our article "The law of independent combination of states of signs", in which we examined how to solve problems in genetics. Dihybrid interbreeding, like the third Mendelian law to which it obeys, is applicable to allelic genes in the homologous chromosomes of each pair.

In the mid-20th century, the American genetic scientist T. Morgan proved that most of the features are controlled by genes that are located on the same chromosome. They have a linear arrangement and form clutch groups. And their number is equal to the haploid set of chromosomes. In the process of meiosis, which leads to the formation of gametes, not the individual genes, as Mendel thought, fall into the sex cells, but the whole of their complexes, called the clusters of Morgan.

Crossing-over

During prophase I (it is also called the first division of meiosis) between internal chromatids of homologous chromosomes, there is an exchange of sites (lucus). This phenomenon has received the name of crossing-over. It underlies hereditary variability. Crossing-over is especially important for studying the sections of biology dealing with the study of hereditary human diseases. Applying the postulates set forth in the chromosome theory of Morgan's heredity, we will define an algorithm that answers the question of how to solve problems in genetics.

Gender-linked inheritance cases are a particular case of the transfer of genes that are located on the same chromosome. The distance that exists between the genes in the clutch groups is expressed as a percentage - morganids. And the cohesion between these genes is directly proportional to the distance. Therefore, crossing-over often occurs between genes that are located far apart. Consider the phenomenon of concatenated inheritance in more detail. But in the beginning we will recall what elements of heredity are responsible for the sexual characteristics of organisms.

Sex chromosomes

In the human karyotype, they have a specific structure: in female individuals they are represented by two identical X chromosomes, and in men in the sex pair, besides the X chromosome, there is also the Y variant, which differs both in form and in the set of genes. This means that it is not homologous to the X chromosome. Such hereditary human diseases as hemophilia and color blindness, arise from the "breakage" of individual genes in the X chromosome. For example, from the marriage of a carrier of hemophilia with a healthy man, it is possible the birth of such offspring.

The above mentioned course of genetic crossing confirms the fact of the adhesion of the gene controlling the clotting of blood to the sex X chromosome. This scientific information is used to teach students methods that determine how to solve problems in genetics. 11th grade has a program in biology, in which such sections as "genetics", "medicine" and "human genetics" are considered in detail. They allow students to study human hereditary diseases and know the reasons for their occurrence.

Interaction of genes

The transfer of hereditary traits is a rather complex process. The above schemes become clear only if students have a basic minimum of knowledge. It is necessary, as it provides mechanisms that give an answer to the question of how to learn to solve problems in biology. Genetics studies the forms of gene interaction. This is the polymer, epistasis, complementarity. Let's talk about them in more detail.

An example of inheritance of hearing in a person is an illustration of this type of interaction, such as complementarity. Hearing is controlled by two pairs of different genes. The first is responsible for the normal development of the cochlea of the inner ear, and the second is responsible for the functioning of the auditory nerve. In the marriage of deaf parents, each of which is a recessive homozygote for each one of the two pairs of genes, children with normal hearing are born. In their genotype, there are both dominant genes that control the normal development of the hearing aid.

Pleiotropy

This is an interesting case of gene interaction, in which the phenotypic manifestation of several features depends on one gene present in the genotype. For example, in western Pakistan, human populations of some representatives have been found. They have no sweat glands in certain areas of the body. Simultaneously, such people were diagnosed with the absence of some molars. They could not form in the process of ontogenesis.

In animals, for example, Karakul sheep, there is a dominant W gene, which controls both the color of fur and the normal development of the stomach. Consider how the gene W is inherited when two heterozygous individuals are crossed. It turns out that in their offspring, one-fourth of the lambs that have the genotype of WW are killed due to abnormalities in the development of the stomach. In this case, ½ (having gray fur) are heterozygous and viable, and ¼ are individuals with black fur and normal development of the stomach (their genotype is WW).

Genotype - whole system

The multiple action of genes, polyhybrid interbreeding, the phenomenon of concatenated inheritance serve as conclusive evidence of the fact that the aggregate of the genes of our organism is an integral system, although it is represented by individual gene alleles. They can be inherited according to the laws of Mendel, independently or loci, linked according to the postulates of Morgan's theory. Examining the rules responsible for how to solve problems in genetics, we were convinced that the phenotype of any organism is formed under the influence of both allelic and non-allelic genes influencing the development of one or several characteristics.