7. Classical Genetics

The Classical Genetics, also known as Mendelian Genetics, is one of the main topics of the study of Biology for the ENEM test. It is based on the pioneering work of the monk Gregor Mendel, who in the 19th century experimented with peas and formulated the fundamental laws of heredity.

To understand Classical Genetics, we need to start with understanding some fundamental concepts. The first is the concept of genes, which are segments of DNA that determine hereditary characteristics. Each gene has a specific location on a chromosome known as a locus.

The alleles are different versions of the same gene, which can result in different manifestations of a trait. For example, a gene might have alleles for blue or brown eye color. Each individual has two alleles for each gene, one inherited from each parent. If the two alleles are the same, the individual is homozygous for that gene; if the alleles are different, the individual is heterozygous.

Mendel formulated two fundamental laws of heredity. Mendel's First Law, or Law of Segregation, states that the two alleles for each trait separate during the formation of gametes, so that each gamete receives only one allele of each gene.

Mendel's Second Law, or the Law of Independent Assortment, states that the segregation of alleles for one gene does not affect the segregation of alleles for another gene. This means that hereditary traits are inherited independently of each other. However, this law only applies when the genes are on different chromosomes or are very far apart on the same chromosome.

Classical Genetics also involves the study of inheritance patterns, which can be dominant, recessive, co-dominant or sex-linked. Dominant inheritance occurs when one allele dominates the other and determines the trait in the phenotype, even when it is only present in one copy. Recessive inheritance occurs when an allele can only determine the trait in the phenotype if it is present in two copies.

Co-dominant inheritance occurs when both alleles are expressed in the phenotype. Sex-linked inheritance occurs when the gene is located on the sex chromosome, usually the X chromosome. Sex-linked traits are more often expressed in males, who have only one X chromosome, while females have two.

Finally, Classical Genetics also includes the study of mutations, which are changes in DNA that can result in new alleles. Mutations can be caused by DNA replication errors, exposure to radiation, or chemicals. They can have varying effects, from no effect at all to causing serious illness or evolutionary advantages.

In summary, Classical Genetics is an essential topic for the study of Biology for the ENEM test. It provides the basis for understanding how traits are inherited and how genetic diversity is generated. Through the study of Classical Genetics, students can better understand the complexity and beauty of life on our planet.

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