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The Genetic Code

Chapter 3

DNA (deoxyribonucleic acid) The chemical composition of the molecules that contain the genes, which are the chemical instructions for cells to manufacture various proteins.
Chromosome One of the 46 molecules of DNA 9 (in 23 pairs) that virtually each cell of the human body contains and that together, contain all the genes. Other species have more or fewer chromosomes.
Gene A small section of a chromosome; the basic unit for the transmission of heredity. A gene consists of a string of chemicals that provide instructions for the cell to manufacture certain proteins.
Allele A variation that makes a gene different in some way from other genes for the same characteristics. Many genes never vary; others have several possible alleles.
Genome The full set of genes that are the instructions to make an individual member of a certain species.
Zygote The single cell formed from the union of two gametes, a sperm and an ovum.
Gamete A reproductive cell; that is a sperm or ovum that can produce a new individual if it combines with a gamete from the other sex to make a zygote.
Genotype An organism's entire genetic inheritance, or genetic potential.
Homozygous Referring to two genes of one pair that are exactly the same in every letter of their code. Most gene pairs are homozygous.
23rd Pair The chromosome pair that, in humans determines sex. The other 22 pairs are autosomes; inherited equally by males and females.
XX A 23rd chromosome pair that consists of two x shaped chromosomes, one from mother and one from father. XX zygotes become females.
XY A 23rd chromosome pair that consists of an X-shaped chromosome from the mother and Y-chromosome from the father. XY zygotes become males.
Stem Cells Cells from which any other specialized type of cell can form.
Monozygotic Twins Twins who originate from one zygote that splits apart very early in development. (a.k.a identical twins). Other monozygotic multiple births (such as triplets) can occur.
Dizygotic Twins Twins who are formed when two separate ova are fertilized by two separate sperm at roughly the same time. (a.k.a fraternal twins)
Assisted Reproductive Technology ( ART ) A general term for the techniques designed to help infertile couples conceive and then sustain a pregnancy.
In Vitro Fertilization (IVF) Fertilization that takes place outside a woman's body (as in a glass laboratory dish). The procedure involves mixing the sperm with ova that have been surgically removed from the woman's ovary. If zygote is produced, then it is inserted into the woman.
Phenotype The observable characteristics of a person, including appearance, personality, intelligence, and all other traits.
Multifactorial Referring to a trait that is affected by many factors, both genetic and environmental expression; enhancing, halting, shaping, or altering the expression of genes, resulting in phenotype, that may differ from genotype.
Epigenetic Referring to environment factors that affect genes and genetic expression; enhancing, halting, shaping, or altering the expression of genes, resulting in a phenotype that may differ markedly from the genotype.
Polygenic Referring to a trait that is influenced by many genes.
Human Genome Project An international effort to map the complete human genetic code, This effort was essentially completed in 2001, though analysis is ongoing.
Dominant-Recessive Pattern The interaction of a heterozygous pair of alleles in such a way that the phenotype reveals the influence of one allele (the dominant gene) more than that of the other (the recessive gene).
Carrier A person whose genotype includes a gene that is not expressed in the phenotype. Such an unexpressed gene occurs in half of the carrier's gametes and thus is passed on to half of the carrier's children, who will likely be carriers, too.
X-linked Referring to a gene carried on the X chromosome. If a male inherits an X-linked recessive trait from his mother, he expresses that trait because the Y from his father has no counteracting gene. Females are more likely to be carriers of the X-linked trait
Heritability A statistic that indicates what percentage of the variation in a particular trait within a particular population, in a particular context and era, can be traced to genes.
Down Syndrome (a.k.a trisomy-21) A condition in which a person has 47 chromosomes instead of the usual 46, with 3 rather than 2 chromosomes at the 21st site. People with Down syndrome typically have distinctive characteristics, including unusual facial features, heart abnormalities.
Huntington disease A fatal central nervous system disorder caused by a genetic miscode- more than 35 repetitions of a particular triplet.
Fragile X syndrome A genetic disorder in which part of the X chromosome seems to be attached to the rest of it by a very thin string of molecules. The cause is a single gene that has more than 200 repetitions of one triplet.
Genetic Counseling Consultation and testing by trained experts that enable individuals to learn about their genetic heritage, including harmful conditions that they might pass along to any children they may conceive.
Phenylketonuria (PKU) A genetic disorder in which a child's body is unable to metabolize an amino acid called phenylalanine. Unless the infant immediately begins a special diet, the resulting buildup of phenylalanine in body fluids causes brain damage.
Created by: aglana