How Are Traits Passed From One Generation to the Next?

Genetic traits are passed through DNA.

While some traits are merely habits or social rules picked up from the environment (such as an accent or certain mannerisms while walking) others are influenced by genetic information. This is how you can "inherit" your father's nose or your grandmother's eyes--the information is passed down through DNA.

DNA, Genes and Alleles

DNA (deoxyribonucleic acid) is a strand of 23 pairs of chromosomes, with one chromosome in a pair coming from each parent. These 46 chromosomes contain hundreds of individual genes, which are sequences or combinations of information that transfer traits from parents to children.

An allele is a variation in genetic information. You inherit two alleles for each gene. If your DNA has variations of alleles for eye color (or shape or size or anything else) this mean you have the genetic material for those eye colors.

Recessive Genes

Recessive genes are those that can only be expressed when both parents provide the same trait. For example if one parent has red hair and the other blond, their children we will be born with blond hair, because red hair is a heterozygous trait (a pair of dominant and recessive genes). This means that a redhead likely had one blond parent and one dark brown/black haired parent, making the blond genetic information dominant. Homozygous traits are those that occur when two recessive genes of the same type are paired together, making them a dominant gene.

Dominant Genes

Dominant genes are genetic traits from one copy of a gene (from only one parent) that will always express when present in a pair of genes.

Mutation

Genetic mutation is a permanent change in the DNA sequence. Gene mutations can be inherited or acquired during a person's lifetime. Hereditary/germline mutations are passed from parent to child and are present in almost every cell. De novo mutations are those that occur in the sperm cell, egg or just after fertilization. Somatic/acquired mutations are those that occur in certain cells during the persons life and can be caused by environmental factors or when DNA replicates itself incorrectly (such as in some cancers).

Heredity and Evolution

Heredity is how traits and characteristics are transferred from parent to offspring. Because DNA is at its core simply a resilient strand of chemical compounds, it can be affected by many things. Evolution has historically been the process of gradual genetic change, but in recent times genetic information is apparently being altered more rapidly by chemical damage. This appears to be causing damage to those with weaker immune systems by "turning on" recessive traits for certain illnesses and or disabilities. Some hypothesize that this may be one cause of autism and similar disorders with a genetic component.

References

• Allele--Glossary Entry: Genetics Home Reference
• Discrete Genes Are Inherited: Gregor Mendel
• Genetics
• Genes and Health, Dominant Traits, Recessive Traits
• Cayman Chemical I DNA/RNA Damage Monoclonal Antibody (Clone 15A3)

Resources

• What Is a Gene Mutation and How do Mutations Occur?
• Chromosome Mutations--Biology Online