DNA (deoxyribonucleic acid)
The molecular basis of heredity, constructed of a double helix whose parallel strands consist of both pairs held together by hydrogen bonds
Chromosome
A carrier of genes; one of the 46 molecules of DNA (in 23 pairs) that each cell of the body contains an that, together, contain all human genes
Genome
The full set of chromosomes, with all the genes the contain, that make up the genetic material of an organism
Gene
The basic unit for the transmission of heredity instructions
Gamete
A reproductive cell; that is, a cell that can reproduce a new individual if it combines with a gamete from the other sex
Zygote
The single cell formed from the fusing of a sperm and an ovum
Genotype
An organism's entire genetic inheritance or genetic potential
Allele
A slight, normal variation of a particular gene
23rd pair
The chromosome pair that, in humans, determines the zygote's (and hence the person's) sex, among other things
XX
A 23rd pair that consists of two X-shaped chromosomes, one from the mother and one from the father
XY
A 23rd pair that consists of one X-shaped chromosome from the mother and one Y-shaped chromosome from the father
spontaneous abortion
The naturally occurring termination of a pregnancy before the fetus is fully developed. Also called miscarriage
Monozygotic twins
Twins who have identical genes because they were formed from one zygote that split into two identical organisms very early in development
Dizygotic twins
Twins who were formed when two separate ova were fertilized by two separate sperm at roughly the same time. Such twins share about half their genes, like any other siblings
on-off switching mechanisms
Processes in which certain genes code for proteins that switch other genes on and off, making sure that the other genes produce proteins at the appropriate times
phenotype
A person's actual appearance and behavior, which are the result of both genetic and environmental influences
Multifactorial
Referring to inherited traits that are influenced by many factors, including factors in the environment, rather than b genetic influences alone
Polygenic
Referring to inherited traits that are influenced by many genes, rather than by a single gene
Additive gene
A gene that, through interaction with other genes, affects a specific trait (such as skin color or height)
dominant-recessive pattern
The interaction of a 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 (recessive gene)
dominant gene
The member of an interacting pair of alleles whose influence is more evident in the phenotype
recessive gene
The member of an interacting pair of alleles whose influence is less evident in the phenotype
X-linked
Referring to a gene that is located on the X chromosome
Human Genome Project
An international effort to map the complete human genetic code
Carrier
A person whose genotype includes a gene that is not expressed in his or her phenotype but can be passed on to his or her children
Behavior genetics
The study of the genetic origins of psychological characteristics, such as personality patterns, psychological disorders, and intellectual abilities
Fragile X Syndrome
A genetic disorder in which part of the X chromosome is attached to the rest of it by a very thin string of molecules; often produces mental deficiency in males who inherit it
genetic counseling
A process of consultation and testing that enables individuals to learn about their genetic heritage, including conditions that might harm any children they may have
Mosaic
Referring to a condition in which a person has a mixture of cells, some normal and some with the incorrect number of chromosomes