Hugo de Vries is known chiefly for suggesting the concept of genes, rediscovering the laws of heredity in the 1890s while unaware of Gregor Mendel's work, for introducing the term mutation, and for developing a mutation theory of evolution.

Genetics is the science of genes, heredity, and variation in living organisms. Genetics deals with the molecular structure and function of genes, with gene behavior in the context of a cell or organism with patterns of inheritance from parent to offspring, and with gene distribution, variation and change in populations.

Gregor Johann Mendel figure-head of the new science of genetics for his study of the inheritance of certain traits in pea plants. Mendel showed that the inheritance of these traits follow particular laws, which were later named after him. He is known as the father of genetics.

A deleterious mutation has a negative effect on the phenotype, and thus, decreases the fitness of the organism.

Loss-of-function mutations are the result of gene product having less or no function. When the allele has a complete loss of function (null allele) it is often called an amorphic mutation. Phenotypes associated with such mutations are most often recessive. It is not a point mutation.

Most amino acids are encoded by several different codons. For example, if the third base in the TCT codon for serine is changed to any one of the other three bases, serine will still be encoded. Such mutations are said to be silent because they cause no change in their product and cannot be detected without sequencing the gene (or its mRNA).

Monosomy refers to lack of one chromosome of the normal complement. Partial monosomy can occur in unbalanced translocations or deletions, in which only a portion of the chromosome is present in a single copy. Monosomy of the sex chromosomes (45X) causes Turner syndrome.

William Bateson was the first person to use the term genetics to describe the study of heredity and biological inheritance, and the chief populariser of the ideas of Gregor Mendel .

Frameshift mutation is a mutation caused by insertion or deletion of a number of nucleotides that is not evenly divisible by three from a DNA sequence. Due to the triplet nature of gene expression by codons, the insertion or deletion can disrupt the reading frame, or the grouping of the codons, resulting in a completely different translation from the original. The earlier in the sequence the deletion or insertion occurs, the more altered the protein produced is.

Genetic engineering is also called genetic modification. It is the direct human manipulation of an organism's genome using modern DNA technology. It involves the introduction of foreign DNA or synthetic genes into the organism of interest.

In genetics, a chromosome translocation is a chromosome abnormality caused by rearrangement of parts between nonhomologous chromosomes. A gene fusion may be created when the translocation joins two otherwise separated genes, the occurrence of which is common in cancer.

While Mendel's research was with plants, the basic underlying principles of heredity that he discovered also apply to people and other animals.Through the selective cross-breeding of common pea plants (Pisum sativum) over many generations, Mendel discovered that certain traits show up in offspring without any blending of parent characteristics.

Genetic recombination is a process by which a molecule of nucleic acid is broken and then joined to a different one. Recombination can occur between similar molecules of DNA, as in homologous recombination, or dissimilar molecules, as in non-homologous end joining. Recombination is a common method of DNA repair in both bacteria and eukaryotes.

Homologous recombination is a type of genetic recombination in which nucleotide sequences are exchanged between two similar or identical molecules of DNA. It is most widely used by cells to accurately repair harmful breaks that occur on both strands of DNA, known as double-strand breaks.

Insertions add one or more extra nucleotides into the DNA. They are usually caused by transposable elements, or errors during replication of repeating elements, e.g. AT repeats. Insertions in the coding region of a gene may alter splicing of the mRNA (splice site mutation), or cause a shift in the reading frame (frameshift), both of which can significantly alter the gene product.

It has a short generation time (about 10 days at room temperature) so several generations can be studied within a few weeks.

Phenylketonuria (PKU) is an autosomal recessive metabolic genetic disorder characterized by an error in the genetic code for the hepatic enzyme phenylalanine hydroxylase (PAH), rendering it nonfunctional.This enzyme is necessary to metabolize the amino acid phenylalanine (Phe) to the amino acid tyrosine.

Drosophila melanogaster is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is commonly known as the common fruit fly or vinegar fly.

A single gene disorder is the result of a single mutated gene. There are estimated to be over 4000 human diseases caused by single gene defects. Single gene disorders can be passed on to subsequent generations in several ways.

Lethal mutations are mutations that lead to the death of the organisms which carry the mutations.

Huntington's disease, is a neuro-degenerative genetic disorder that affects muscles coordination and leads to cognitive decline and dementia. It typically becomes noticeable in middle age.

Nucleic acid analogues are compounds structurally similar (analog) to naturally occurring RNA and DNA, used in medicine and in molecular biology research.

Marfan syndrome is a genetic disorder of the connective tissue. People with Marfan's tend to be unusually tall, with long limbs and long, thin fingers.

A gene is a unit of heredity in a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living things depend on genes, as they specify all proteins and functional RNA chains.

A cell is said to be homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes. The cell or organism in question is called a homozygote. True breeding organisms are always homozygous for the traits that are to be held constant.