What does the chromosomal theory of heredity say?
The chromosomal theory of heredity is based on the knowledge of scientists about the structure of genes and their transfer to next generations. This makes it possible to answer some questions related to our origin, appearance, behavior, diseases, etc. The chromosomal theory of heredity consists in the order of transferring information from parents to children in the genes that add up to a new person.
Information is inherited through thousands of genes that are in the nuclei of the egg and sperm, forming a new organism. Each gene has a code that synthesizes one specific type of protein. This process is streamlined, which makes it possible to predict the features of the future generation. This is because the genes (units of inheritance) are combined in a specific order. Interesting is the fact that each cell contains a pair of chromosomes responsible for one protein.Thus, each gene is paired (allelic). One of them dominates, the other is in a "sleeping" state. This is inherent in all cells of the body, except sex (they have only one DNA strand in order to form a full-fledged nucleus with a full set of chromosomes during a fusion into a zygote). These simple truths are called the “chromosomal theory of heredity,” or the genetics of Mendel.
During the formation of gametes, pairs of genes diverge, but during fertilization, something else happens: the genes of the egg cell and the sperm cell combine. The new combination makes it possible to identify the development of certain characteristics of the offspring. Since each parent has allelic genes, they cannot predict which ones will be passed on to the child. Of course, according to one of Mendel's laws, the dominant genes are stronger, and therefore there is a high probability that they will manifest in the child, but everything depends on the case.
Human chromosomes are 23 pairs. Sometimes the kit may be incorrect as a result of the attachment of an extra gene. Then various kinds of mutations can occur. This is also called “chromosomal syndrome” - a change in the structure of the DNA chain: inversion of the chromosome, its loss, duplication, rearrangement in a certain region.It is also possible to exchange sections of unlike chromosomes, rearrange a specific region, or transfer a gene from one chromosome to another. Vivid examples of such manifestations are the following diseases.
1. Feline cry syndrome
The chromosomal theory of heredity confirms that such a violation is caused by the loss of the short arm of the fifth chromosome. This disease is manifested in the first minutes of life in the form of crying, similar to the cat "meow." After a few weeks, this symptom disappears. The older the child, the stronger the anomalous development is visible: first, it is distinguished by its low weight, then the asymmetry of the face is more and more noticeable, microcephaly is manifested, the eyes are slanting, the nose is wide, abnormal ears with an external auditory canal, heart disease is possible. Physical and mental retardation is an integral part of the disease.
2. Genomic mutations
- Aneuploidy(not a multiple of the haploid set of chromosomes). A vivid example is Edwards syndrome. Manifested in childbirth in the early stages, the fetus has hypoplasia of skeletal muscles, light weight, microcephaly. The presence of a “cleft lip”, the absence of a big toe on the legs, defects of internal organs, and their abnormal development are determined.Only a few survive and remain mentally retarded throughout life.
- Polyploidy(multiple of chromosomes). Patau syndrome is manifested by external and mental abnormalities. Children are born deaf, lagging behind in mental development. The chromosomal theory of heredity is always confirmed, which allows predicting the development of the fetus in the womb and, if necessary, terminate the pregnancy.