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On-line Ed Kit

Basic Genetics- A Glossary of Genetic Terms

human cell Human cell

Almost all of the 100 trillion cells in the human body contain a copy of the entire human genome, the complete set of genetic instructions necessary to build a human being.
cell nucleus Cell nucleus

The nucleus is a separate compartment in the cell that contains 6 feet of DNA packed into 23 pairs of chromosomes. We each inherit one set of 23 chromosomes from our mother, and another set from our father. Egg and sperm cells carry single sets of 23 chromosomes.
chromosomes Chromosome

Each of the human chromosomes contains hundreds to thousands of genes, the major functional units of DNA.

Each gene contains a segment of DNA, typically several thousand base
pairs long, that is
gene   copied into a molecule of RNA. Usually, the information in RNA is translated to make a protein.


DNA, or deoxyribonucleic acid, is a long molecule made of two twisting, paired strands. Each strand is made of four chemical units, called nucleotide bases, strung together in a precise
deoxyribonucleic acid order, just as letters string together to make specific words. The bases are adenine (A), guanine (G), cytosine (C), and thymine (T). The bases on opposite strands pair specifically; an A always pairs with a T, and a C always with a G. Each such pair is called a base pair of DNA

ribonucleic acid RNA

RNA, or ribonucleic acid, is chemically similar to DNA, except it is single-stranded, not dou- ble-stranded; it contains the base uracil (U) instead of thymine (T); it can migrate out of the nucleus. The sequences of most RNA molecules are translated to make proteins.
A Protein Protein

Proteins make up essential parts of tissues and guide chemical reactions in living things. They are made of 20 different building blocks called amino acids. The DNA sequence of a gene determines the amino acid sequence of the protein that gene encodes. The amino acid sequence of the protein is, in turn, responsible for the protein's shape and function.
A Genome Genome

A genome is all the DNA - the complete genetic inheritancein an organism. The human genome is contained in 23 pairs of chromosomes housed in the nucleus and the small circle of DNA present in mitochondria, the organelles that process energy. The number of genes in the approximately 3 billion base pairs of human DNA is still not known, but is probably between 35,000 and 100,000.


Pronounced "snip," SNPs are single-nucleotide polymorphisms or one-letter variations in the DNA sequence. SNPs contribute to differences among
SNP diagram   individuals. The majority have no effect, others cause subtle differences in countless characteristics, like appearance, while some affect the risk for certain diseases.


Mutations are changes in DNA spelling that can prevent proteins from functioning normally and cause health problems. Three DNA bases are deleted in the mutated sequence, resulting in the deletion of an amino acid (phenylalanine) from the CF
Mutation Diagram   protein. People with the abnormal protein develop cystic fibrosis Three DNA bases are deleted in the mutated sequence, resulting in the deletion of an amino acid (phenylalanine) from the CF protein.










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