Research into modes and mechanisms of epigenetic inheritance is still in its scientific infancy, but this area of research has attracted much recent activity as it broadens the scope of heritability and evolutionary biology in general. These phenomena are classed as epigenetic inheritance systems that are causally or independently evolving over genes. Recent findings have confirmed important examples of heritable changes that cannot be explained by direct agency of the DNA molecule. Developmental biologists suggest that complex interactions in genetic networks and communication among cells can lead to heritable variations that may underlie some of the mechanics in developmental plasticity and canalization. However, while this simple correspondence between an allele and a trait works in some cases, most traits are more complex and are controlled by multiple interacting genes within and among organisms. If a mutation occurs within a gene, the new allele may affect the trait that the gene controls, altering the phenotype of the organism. DNA sequences can change through mutations, producing new alleles. If the DNA sequence at a particular locus varies between individuals, the different forms of this sequence are called alleles. The specific location of a DNA sequence within a chromosome is known as a locus. Organisms inherit genetic material from their parents in the form of homologous chromosomes, containing a unique combination of DNA sequences that code for genes. Within cells, the long strands of DNA form condensed structures called chromosomes. A portion of a DNA molecule that specifies a single functional unit is called a gene different genes have different sequences of bases. Before a cell divides through mitosis, the DNA is copied, so that each of the resulting two cells will inherit the DNA sequence. The Nucleic acid sequence (the sequence of bases along a particular DNA molecule) specifies the genetic information: this is comparable to a sequence of letters spelling out a passage of text. DNA is a long polymer that incorporates four types of bases, which are interchangeable. ![]() Heritable traits are known to be passed from one generation to the next via DNA, a molecule that encodes genetic information. However, some people tan more easily than others, due to differences in their genotype: a striking example is people with the inherited trait of albinism, who do not tan at all and are very sensitive to sunburn. ![]() ![]() For example, suntanned skin comes from the interaction between a person's genotype and sunlight thus, suntans are not passed on to people's children. As a result, many aspects of an organism's phenotype are not inherited. These traits arise from the interaction of its genotype with the environment. ![]() The complete set of observable traits of the structure and behavior of an organism is called its phenotype. Inherited traits are controlled by genes and the complete set of genes within an organism's genome is called its genotype. In humans, eye color is an example of an inherited characteristic: an individual might inherit the "brown-eye trait" from one of the parents. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.
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