Glossary Terms: A - D

Terms

  1. Allele

  2. Autosome

  3. Base

  4. Cell

  5. Chromosome

  6. Darwin, Charles

  7. DNA

  8. Double Helix

Definitions

  1. Allele

    An allele is a variant form of a gene. When a genes varies (genes for eye color, for example, could be blue or brown) each individual form is called an allele.

  2. Autosome

    Autosomes are the non-sex chromosomes (carriers of DNA). Each human cell has 23 pairs of chromosomes: 22 autosomal pairs and one sex pair.

  3. Base

    Nucleotide bases are the chemical building blocks of DNA, which pair up in a double helix structure and serve as a genetic alphabet with which we form sentences (or genes). There are four kinds of bases (A, C, G, and T).

  4. Cell

    Cells are the basic units for life. The human body is made of some 50 trillion to 100 trillion cells, which combine to form more complex tissues and organs. Most cells have a similar basic structure. An outer layer, called the cell membrane, contains fluid called cytoplasm. Within the cytoplasm are many different, specialized “little organs” called organelles. The most important of these is the nucleus, which controls the cell and houses a person’s genetic material in structures called chromosomes. Another type of organelle is the mitochondrion. This “cellular power plant” has its own genetic material, which we can study to trace family history.

  5. Chromosome

    A chromosome is the carrier of DNA. Inside most of your cells there are exactly 23 pairs of chromosomes. Chromosomes are paired because you inherit one copy from your mother and one from your father.

  6. Darwin, Charles

    Charles Darwin’s 1859 book The Origin of Species promoted a theory of evolution by natural selection and challenged Victorian-era ideas about the role of humans in the universe. Darwin’s theories were based on a constantly evolving natural world and held that each generation of a species had to compete for survival. Survivors held some natural advantages over their less fortunate relatives and passed those characteristics on to their progeny, thus over-representing these favored genetic types in the next generation. Darwin also advanced the idea that species were descended from a common ancestor. Darwin’s work became the foundation of modern evolutionary theory.

  7. DNA

    DNA (deoxyribonucleic acid) is the set of genetic instructions for creating an organism. DNA molecules are shaped like a spiral staircase called a double helix. Each step is composed of DNA bases (A, C, G, and T). Scientists can read your specific sequence of DNA bases and use that information to trace your ancestors’ journey.

  8. Double Helix

    The shape of DNA, similar to that of a spiral staircase or twisted ladder. The stairway’s railings are composed of sugars and phosphates. Its sides contain the patterned base pairs: A, T, C, and G. When a cell divides for reproduction, the helix unwinds and splits down the middle like a zipper in order to copy itself.