Genetics is defined as the science that studies genes, the basic unit that transmits genetic traits from parents to children, as well as the deoxyribonucleic acid that makes up genes and its impact on the interactions that occur in living cells. Genetics also studies the role of genetic factors in the emergence of genetic traits.
Gregor Mendel, a scientist who discovered the principles that govern the transmission of genetic features from one generation to the next in the mid-nineteenth century without understanding anything about the physical or chemical basis of genes, is credited with the establishment of genetics. Name the "factors" or "units." The term genetics was coined in 1905 by William Bateson, an English biologist who was a strong supporter of Mendel's concepts and research.
The evolution of genetics
There is no doubt that genetics has piqued people's interest since the dawn of time. For example, one of the Babylonian tablets dating back over 6000 years illustrates the family tree of several horses and suggests some features that can be inherited, and ancient carvings show cross-pollination (cross-pollination) of palm trees. It was during the period of the ancient Greeks.
The scientist Hippocrates proposed the pangenesis hypothesis, which states that the parents' organs form invisible seeds that are transmitted through sexual intercourse to the mother's womb, where they reshape themselves to form a child, while the scientist Aristotle assumed that the blood is responsible for the transmission of genetic traits from one generation to the next. The male's semen was thought to be pure blood, and the female's blood during menstruation was thought to be identical to the male's semen, and that a child would be created from their union in the mother's womb.
The heredity concept of acquired features, as well as the hypothesis of use and neglect, were proposed by the French scientist Jean- Baptiste Lamarck. As a result of deer-like creatures attempting to reach the foliage of lofty trees by extending their necks for longer lengths. Following that, scientists Alfred Russel Wallace and Charles Darwin offered the notion of natural selection, with Darwin assuming that humans and animals have a common ancestor, but these theories appeared to be at odds with Mendel's genetic tests at the time.
Mendel's adventures in the globe
Mendel began his research in 1856 with mice and honeybees, but he eventually concluded that the pea plant would be the best model for his experiments.
The length of the plant, the color of the blossom, the color of the seeds, and the shape of the seeds were among the seven genetic features Mendel analyzed in the pea plant, one at a time. To do so, he first verified the purity of the genetic trait under investigation (pure implies coming from the union of two similar genes), which he accomplished by letting plants carrying the trait for numerous generations to fertilize themselves. The trait is confirmed in all of the offspring, and after obtaining seeds from plants with pure traits, Mendel continued his research by undertaking the following steps:
- Pollination by cross-pollination: Mendel fertilized a plant with the first pure characteristic (for example, a long-stemmed plant) with pollen from a plant having the opposing pure trait (for example, a short-stemmed plant). The dominant characteristic was the one that appeared, while the recessive trait was the one that disappeared.
- Self-pollination: Mendel allowed the long-stemmed plants that emerged as a result of cross-pollination to pollinate themselves, resulting in the emergence of a small percentage of short-stemmed plants; it was discovered that for every three plants bearing the dominant trait (long-stemmed), one plant bearing the recessive trait (short-stemmed) appeared, indicating that the number of long-stemmed pea plants outnumbered the number of short-stemmed pea plants. Mendel observed that the inheritance of the stem length characteristic had no effect on the inheritance of other traits, such as bloom color.
Mendel's experiments yielded the following results.
- A pair of factors that can be inherited, i.e. passed down from parents to offspring, regulate the emergence of a genetic trait. (The factors are genes, but the term did not exist at the time of Mendel.)
- One factor can hide the influence of another, and the dominant factor is referred to as such, while the recessive factor is referred to as such.
- During the production of gametes, the pair of factors splits, with one factor being randomly sent to the female gamete and the other being randomly transmitted to the male gamete.
- The factors that regulate the appearance of one hereditary feature are inherited separately from the factors that control the appearance of other hereditary traits.
Mendel's prior research assumed that when the dominant and recessive genes mix, the dominant gene masks the influence of the recessive gene. When the gene responsible for the shape of smooth seeds combines with the gene responsible for the shape of wrinkled seeds, the seeds appear smooth because the gene responsible for the shape of smooth seeds completely dominates and hides the effect of the gene responsible for the shape of wrinkled seeds, and this is a principle called Complete Dominance, which controls the shape of the seeds in addition to the traits that Mendel worked on, but there are other types of genetic traits, called non-Mendelian traits; Because Mendel's laws do not:
- Dominance that isn't complete: The nature of human hair is an example of traits that are subject to incomplete dominance laws; the dominant gene in this type of inheritance is the curly hair gene, and the recessive gene is the smooth hair gene; when the two genes come together, one does not cancel out the influence of the other, as it does in complete sovereignty, but a third characteristic appears intermediate between them, which is wavy hair. The inheritance of the color of the flowers of the nightingale plant is another example of imperfect dominance; when the dominant red nightflower color gene combines with the recessive white flower color gene, an intermediate characteristic appears between red and white, which is called the nightingale flower color which is pink flowers
- Co-dominance: varies from full and incomplete sovereignty in that there is no recessive trait in this form of hereditary trait, which may be seen in the inheritance of hair color in some cow breeds. The combined influence of both genes.
- Genes that are lethal: The meeting of two dominant genes results in the death of the organism in this type of inheritance. The hair color of house mice is an example of this type of inheritance; the dominant gene is yellow color, and the recessive gene is lead color (aguti), and when the two recessive lead color genes are combined, all individuals appear gray, whereas the combination of the two dominant genes, i.e. the yellow color genes, has a fatal effect on mice embryos, leading to their death - i.e. Fetuses - early in pregnancy.