The 3:1 phenotypic ratio of yellow: green color and the 3:1 ratio of the round: wrinkled seed shape during monohybrid crossing was also maintained in the dihybrid cross. Thus, he came to the conclusion that the characters are distributed independently and inherited independently. Based on this observation, he developed his third law – the law of independent assortment. To define an independent assortment, you must first understand the law of separation. The law of segregation states that during meiosis, different gamete cells receive two different genes, sorted independently. On the other hand, the two maternal and paternal DNA are separated randomly, which allows for a greater diversity of genes. The law of independent sorting appears during the random division of maternal and paternal DNA sources. Due to random selection, the gamete may receive maternal genes, paternal genes, or a mixture of both. Genetic distribution is based on the initial stage of meiosis, in which these chromosomes are arranged randomly. If you have 3/4 yellow and 3/4 round, then independent events predict that 3/4 x 3/4 = 9/16 will be both yellow and round. The proportions of the other three combinations can be calculated in the same way. What is an independent assortment as explained by a suitable example? For example, let`s take a random population of cats and follow two characteristics: eye color (brown or green) and coat color (white or gray).
For example, the dominant allele for eye color is brown eyes (B) and the recessive allele is green eye color (B). As for coat color, suppose that the white fur allele (W) dominates over the gray fur allele (W). Heterozygous cats with dominant traits, brown eyes and white fur produce gametes that are sexually mature. During gamete production, alleles for eye color are sorted independently of alleles for coat color, if we want to rely on the law of segregation. The resulting gamete after meiosis contains random alleles, so if two heterozygous cats are crossed, their offspring are likely to have mixed characteristics. For example, one of the kittens may have a brown eye color (BB or Bb) and a gray coat color (ww). Another kitten may have green eyes (bb) and gray fur (ww). Others may still have brown eyes and white fur (so possible genotypes could be BBWW, BBWw, BbWW, BbWw). Well, that`s just one striking example.
In nature, the characteristics of eye and coat color are polygenic, which means that several alleles are involved in determining the phenotype of offspring. During fertilization (the union of gametes), the alleles are paired and form a zygote. The zygote, which carries two sets of chromosomes (diploid, 2n) from its parents, develops into a new organism that can multiply by forming its own gametes. When forming their own gametes, the paired alleles separated and sorted independently, leaving only one limb in the gamete. Mendel`s law of independent sorting states that the resulting chromosomes are randomly sorted by mixing maternal and paternal chromosomes. Ultimately, the zygote has a mix of chromosomes rather than a defined set of characteristics specific to each parent. Therefore, chromosomes are considered sorted independently, so the zygote will eventually have a combination of different maternal and paternal chromosomes. «The law of independent sorting states that alleles of different genes are inherited independently within sexually reproducing organisms.» Mendel`s experiment showed that alleles for round or wrinkled peas were inherited independently of alleles for yellow or green peas, since the plants were not only round and yellow or green and wrinkled. We now know that they exist on different chromosomes, allowing them to be mixed during the meiosis process.
Mendel presented his work Experiments on Plant Hybrids at two meetings of the Natural History Society of Brno, Moravia, on 8 February and 8 March 1865. [28] It generated some positive reports in local newspapers,[26] but was ignored by the scientific community. When Mendel`s work was published in 1866 in the negotiations of the Naturforschensverein in Brno,[29] it was considered essentially hybridization rather than heredity, had little influence, and was cited only about three times over the next thirty-five years. His work was criticized at the time, but is now considered revolutionary work. [30] Remarkably, Charles Darwin knew nothing about Mendel`s work, and it is considered that if he had known, genetics as it exists today would have taken root much earlier. [31] [32] Mendel`s scientific biography thus provides an example of the failure of obscure and highly original innovators to receive the attention they deserve. [33] After initial experiments with pea plants, Mendel decided to investigate seven traits that seemed to be inherited independently of other traits: seed shape, flower color, seed skin hue, pod shape, immature pod color, flower location, and plant height. He first focused on the shape of the seed, which was square or round. [23] Between 1856 and 1863, Mendel cultivated and tested about 28,000 plants, most of them pea (Pisum sativum) plants.
[24] [25] [26] This study showed that when different varieties were crossed (e.g., tall plants fertilized by short plants), in the second generation, one in four pea plants had purebred recessive traits, two out of four were hybrids, and one in four was purebred dominant. His experiments led him to two generalizations, the law of segregation and the law of independent assortment, which later became known as Mendel`s laws of inheritance. [27] 2. Y is the allele for yellow peas and y for green peas. The R allele produces round peas, while the R allele produces wrinkled peas. Given this information, what will be the phenotype of offspring resulting from a cross between a YYRR individual and a YYRR individual? What does independent assortment mean? The law of independent sorting means that the separate characteristics of the different alleles are inherited independently of the zygote. When the random selection of an allele for a particular characteristic is in no way related to the selection of another allele for another characteristic. The law of independent sorting states that the process of random segregation and sorting of pairs of alleles during gamete formation leads to the production of gametes with all possible combinations of alleles in equal numbers. It is expressed by the heredity of two or more different traits associated with different genes. This is one of Gregor Mendel`s legacy principles based on his work in garden peas.
After the rediscovery of his work, they were accepted and called Mendel`s laws. As you can see, the law of independent sorting occurs when maternal and paternal DNA sources are randomly shared. Sometimes the gamete inherits the maternal version of a gene and sometimes it inherits the paternal version. The version it gets is completely random, depending on the order in which these chromosomes align during the first stage of meiosis. According to the law of independent sorting, the alleles of two other genes are sorted independently into gametes. The allele received for one gene does not affect the allele received for another gene. Around 1900, research to find a successful theory of discontinuous heredity, rather than mixing heredity, led to an independent duplication of his work by Hugo de Vries and Carl Correns and the rediscovery of Mendel`s writings and laws. Both recognized Mendel`s priority, and it is considered likely that de Vries did not understand the results he had found until after reading Mendel. [26] Although Erich von Tschermak was credited with the rediscovery, this is no longer accepted because he did not understand Mendel`s laws. [37] Although de Vries later lost interest in Mendelism, other biologists began to establish modern genetics as a science.