Mutations and the Next Generation

There are two places where mutations can be introduced and carried into the next generation. In the first stages of development, a sperm cell and egg cell fuse. They then begin to divide, giving rise to cells that differentiate into tissue-specific cell types. One early type of differentiated cell is the germ line cell, which may ultimately develop into mature gametes. If a mutation occurs in the developing germ line cell, it may persist until that individual reaches reproductive age. Now the mutation has the potential to be passed on to the next generation. Mutations may also be introduced during meiosis, the mode of cell replication for the formation of sperm and egg cells. In this case, the germ line cell is healthy, and the mutation is introduced during the actual process of gamete replication. Once again, the sperm or egg will contain the mutation, and during the reproductive process, this mutation may then be passed on to the offspring. One should bear in mind that not all mutations are bad. Mutations also provide a species with the opportunity to adapt to new environments, as well as to protect a species from new pathogens. Mutations are what lie behind the popular saying of "survival of the fittest", the basic theory of evolution proposed by Charles Darwin in 1859. This theory proposes that as new environments arise, individuals carrying certain mutations that enable an evolutionary advantage will survive to pass this mutation on to its offspring. It does not suggest that a mutation is derived from the environment, but that survival in that environment is enhanced by a particular mutation. Some genes, and even some organisms, have evolved to tolerate mutations better than others. For example, some viral genes are known to have high mutation rates. Mutations serve the virus well by enabling adaptive traits, such as changes in the outer protein coat so that it can escape detection and thereby destruction by the host's immune system. Viruses also produce certain enzymes that are necessary for infection of a host cell. A mutation within such an enzyme may result in a new form that still allows the virus to infect its host but that is no longer blocked by an anti-viral drug. This will allow the virus to propagate freely in its environment.

Mendel's Laws—How We Inherit Our Genes In 1866, Gregor Mendel studied the transmission of seven different pea traits by carefully test-crossing many distinct varieties of peas. Studying garden peas might seem trivial to those of us who live in a modern world of cloned sheep and gene transfer, but Mendel's simple approach led to fundamental insights into genetic inheritance, known today as Mendel's Laws. Mendel did not actually know or understand the cellular mechanisms that produced the results he observed. Nonetheless, he correctly surmised the behavior of traits and the mathematical predictions of their transmission, the independent segregation of alleles during gamete production, and the independent assortment of genes. Perhaps as amazing as Mendel's discoveries was the fact that his work was largely ignored by the scientific community for over 30 years!

Mendel's Principles of Genetic Inheritance Law of Segregation: Each of the two inherited factors (alleles) possessed by the parent will segregate and pass into separate gametes (eggs or sperm) during meiosis, which will each carry only one of the factors. Law of Independent Assortment: In the gametes, alleles of one gene separate independently of those of another gene, and thus all possible combinations of alleles are equally probable. Law of Dominance: Each trait is determined by two factors (alleles), inherited one from each parent. These factors each exhibit a characteristic dominant, co-dominant, or recessive expression, and those that are dominant will mask the expression of those that are recessive.