Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

adenine (A) - a base in DNA and RNA that always bonds with thymine (T) in DNA, and with uracil (U) in RNA.

alleles - two different forms or versions of a gene that occupy corresponding positions on homologous chromosomes. A person has two alleles of a trait--one from each parent.

amino acids - the basic building blocks of proteins; there are twenty different types linked together in different sequences to form different proteins.

anaphase - the third stage of mitosis in which chromatids move to opposite poles of the cell.

antisense strand - the portion of DNA double helix that is not transcribed during protein synthesis (as opposed to the sense strand).

antisense technology - gene silencing or the process of inactivating a gene.

autosome - any chromosome not involved in sex determination. Twenty two of the human chromosome pairs are autosomes.

bases - the molecular building blocks of DNA and RNA: adenine (A), cytosine (C), guanine (G), thymine (T), and in RNA only, uracil (U). In DNA, A attaches only to T, and C attaches only to G. In RNA, A attaches only to U, and C attaches only to G.

base pairs - the pairs of complementary bases that form the rungs of DNA: adenine (A) pairs with thymine (T), cytosine (C) pairs with guanine (G).

base sequence - the order of bases in DNA.

biotechnology - the use of biological processes to make products.

carrier - an individual who is heterozygous for a recessive trait.

cell - the basic unit of life; the smallest basic part of every living thing that can function by itself. It is made of a nucleus surrounded by cytoplasm, organelles (similar to organs in a body) and proteins. Each cell contains the entire genome.

cell cycle - the time from one cell division to the next. Varies from minutes to days, but the actual division takes less than 10% of the cycle.

centromere - the region on a chromosome that ensures proper pairing of sister chromatids.

chromatin - a complex of protein and DNA that make up chromosomes.

chromosome - a long coiled strand in the nucleus, made up of DNA and protein. There are 46 human chromosomes, each containing DNA for hundreds or thousands of individual genes.

chromosome jumping - the process of moving rapidly up or down a chromosome in search of a particular gene by jumping over uninformative areas of DNA.

chromosome map - a diagram showing the locations and relative spacing of genes along a chromosome.

clone - a genetic duplicate.

cloning - the process of producing a genetically identical group of cells from a single ancestor.

codominant - two genes that are neither dominant or recessive; neither masks the other, as in the case of red geraniums crossed with white geraniums yielding pink geraniums.

codon - a special code to make amino acid; a sequence of three nucleotides.

complementary DNA (cDNA) - a single strand of DNA made in the lab to complement the bases in a strand of messenger RNA.

conserved DNA sequences - sequences that have not changed over time.

controlled breeding - the reproduction of desired characteristics.

crossing-over/recombination - a process of chromsome exchange during cell division, resulting in new combinations of alleles.

cytogenics - the study of the genetic implications of chromosome structure and behavior.

cytoplasm - all the organelles and materials inside a cell between the cell membrane and the nucleus.

cytosine (C) - a base in DNA that always bonds with guanine (G).

daughter cell - one of two cells resulting from cell division.

daughter strand - the DNA, or chromosome, strand newly made.

deletion - the loss of a segment of genetic material.

deoxyribonucleic acid - see DNA

differentiated cells - cells in which some of the DNA shuts off so that the cells can be different; they make liver cell, bone cells, etc.

dihybrid cross - the graphing of two or more traits in a Punnett Square to predict heredity.

diploid - a cell or organism that has two complete sets of chromosomes, as opposed to haploid, or those with only one member of each pair of the same chromosomes.

DNA (deoxyribonucleic acid) - a large double-stranded, spiraling molecule that contains genetic instructions for growth, development and replication. It is organized into bodies called chromosomes and found in the cell nucleus.

DNA fingerprinting - the use of fragments of DNA to identify the unique genetic makeup of an individual. There are the RFLP method and the PCR method.

DNA replication - the process or copying a DNA molecule just before cell division.

DNA sequencing - the process of determining the order of bases in a segment of DNA.

dominant gene - a gene which passes on a certain physical characteristic, dominating over a recessive gene present on another chromosome.

double helix - a common name for DNA, referring to the double-stranded, spiraling structure of the molecule.

egg - the female reproductive cell.

electrophoresis - a method of separating large molecules such as DNA fragments from a mixture of similar molecules.

enzymes - the biological catalysts that speed up a chemical reaction.

eugenics - the use of genetic engineering to produce a superior race.

eukaryotes - all living things whose cells have nuclei (most living things).

excision - the removal of a DNA fragment from a chromosome.

exon - a gene segments that has instructions for making a protein, as opposed to introns, which don’t have these instructions.

founder effect - the change in gene frequency occurring when a population is based on only a few individuals.

fraternal twins - twins resulting from fertilization of separate eggs; genetically related as siblings.

gametes - the sex cells in human beings--sperm in men and ova in women. Each gamete cell has 23 chromosomes, half the number found in other body cells.

gel electrophoresis - see electrophoresis

gene - the unit of heredity in chromosomes; a segment of double-stranded DNA.

gene cloning - the process of separating a gene and making identical copies of it.

gene expression - the way information in a gene is changed to a protein or RNA. The DNA sequence is changed into RNA and usually (not always) then changed into protein.

gene linkage map - a map of relative positions of genes on a chromosome. Genes inherited together are close to each other on the chromosome, and said to be linked. (see gene mapping)

gene locus - the position a gene occupies on a chromosome.

gene mapping - the process of determining the relative positions of genes on a DNA molecule. (see gene linkage map)

gene pool - the genetic make-up of a specific population.

gene silencing - the process of inactivating a gene that may cause disease or be defective in another way.

gene splicing - the process of cutting the DNA of a gene in order to add base pairs.

gene targeting - the process of changing or turning off a particular gene.

gene therapy - a method of treating a disease by exchanging the defective gene causing the disease with a healthy one in a cell.

geneticist - a scientist who studies genes.

gene transcription - the first step in gene expression where the gene’s DNA sequence is copied into messenger RNA.

gene translation - the method where transcribed messenger RNA directs the making of proteins from amino acids.

genetic code - all the genes a living thing has inherited. They determine appearance, function, growth, behavior, etc.

genetic disease - a disease caused by a genetic mutation.

genetic engineering - the technology used to genetically manipulate living cells to produce new chemicals or to perform new functions.

genetic marker - a landmark that identifies a certain spot on a chromosome.

genetics - the study of genes and heredity, or how characteristics are passed from parents to children.

genetic testing or screening - a technique used to find out whether a person or organism has a particular gene.

genome - all the genetic information necessary to build a living organism. It is species-specific.

genotype - all the traits, dominant and recessive, that an organism inherits. This is different from the phenotype, or acquired observable traits.

germ cells - the cells that give rise to sperm or egg.

germplasm - the protoplasm of germ cells containing the chromosomes.

guanine (G) - a base in DNA and RNA that always bonds with cytosine (C).

haploid - cells that have a single set of chromosomes, or half the full set of genetic material, as opposed to diploids. Sperm and egg cells are haploid.

Hardy-Weinberg principle - states that the allele frequency for dominant and recessive alleles remains the same over the generations in a particular population as long as certain conditions exist.

helix - spiral in form.

heredity - all of the traits passed on to children by parents (plant or animal) or the process of transferring these traits.

heteromorphic chromosome pairs - chromosomes that visibly differ, like X and Y.

heterosis/hybrid vigor - the superiority of hybrids.

heterozygous - refers to having dissimilar alleles of one or more genes, as opposed to homozygous.

homologous recombination - the process of replacing one DNA segment with a similar sequence.

homozygous - refers to having an identical pair of alleles, one from each parent, as opposed to heterozygous.

Human Genome Project - a large project to map and sequence all DNA in human chromosomes.

hybrid - a plant or animal that results from two different breeds or varieties of parents; carries two different genes for a characteristic.

hybridization - the cross-fertilization or breeding of plants and animals to get the best.

hybrid vigor/heterosis - the superiority of hybrids.

identical twins - the offspring resulting from a fertilized egg splitting into two separate embryos.

inbreeding - the crossing of two closely related beings.

inbreeding depression - the decrease in health or fertility because of inbreeding.

interphase - the period of cell growth between divisions.

introns - DNA sequences without instructions for making protein that come between those sequences with instructions for making protein (exons). Introns are not in messenger RNA, and it is not known what they are for.

inversion - a mutation occurring where a segment of DNA flips upside down in a sequence, but remains in place.

karyotype - a photograph of a cell’s chromosomes, arranged in order from largest to smallest.

linkage - the tendency of genes on the same chromosome to be associated in inheritance.

linkage group (linked genes) - genes found near each other on a chromosome.

locus - the position of a particular gene on a chromosome.

mass selection - large-scale controlled breeding.

maternal inheritance - the inheritance of a trait from the female gamete.

meiosis - the process of cell division, where the number of chromosomes is reduced by half, then the new cells divide again by mitosis. Results in four daughter cells.

messenger RNA (mRNA) - a single strand of RNA that directs protein production.

metaphase - the second stage of mitosis during which the chromatid pairs align at the cell’s equator.

mitochondria - the part of a cell that turns food into energy for chemical reactions, movement, and growth.

mitosis - cell division resulting in daughter (new) cells that are genetically identical to each other and to the parent; the chromosomes are divided before the cell divides.

molecular genetics - the study of molecules of DNA in order to identify the form and function of the genes in them.

monohybrid cross - the graphing of only one trait in a Punnett Square, used for predicting heredity.

mRNA - see messenger RNA.

multifactorial trait - a trait that is determined by heredity and environment.

mutagens - substances which increase the likelihood of mutations.

mutation - a permanent change in a DNA sequence that can be passed on. It can be a change in genetic information, addition of information, or deletion of information.

natural selection - the process by which only the organisms better adapted to the environment survive and reproduce.

nuclear transfer technology - the process of taking the nucleus with the DNA from one cell and putting it into another.

nucleotide - the building block of DNA (rungs on the “ladder” of the DNA double helix) made up of four molecules that occur in pairs--adenine (A) with thymine (T), and cytosine (C) with guanine (G). Thousands of nucleotides are linked to form a DNA or RNA molecule.

nucleus - the center part of the cell. It contains 6 feet of DNA in 23 pairs of chromosomes and is the largest part of the cell. Living things are divided into eukaryotes (whose cells have nuclei) and prokaryotes (whose cells have no nuclei).

oligonucleotide - a short string of nucleotides; a single-stranded segment of DNA. Used as a probe to find matching sequence of DNA or RNA.

organelle - an organized structure within a cell, with a specific function.

outcrossing - an inbreed crossed with a less related.

ovule - the structure in a seed plant that develops into a seed after fertilization.

ovum - the human female reproductive cell.

parent cell - the original cell before cell division.

paternal inheritance - the inheritance of a trait from the male gamete.

PCR (polymerase chain reaction) - a process developed in mid-1980’s to make a large number of copies of a DNA sequence from very little DNA. It is used in forensics when little DNA is available for testing.

pedigree - a diagram representing family relationships of individuals.

peptide - two or more amino acids linked together.

phenotype - all the observable traits a person inherits, as opposed to the genome, or all the traits inherited.

plasma membrane - the fatty layer surrounding the molecules of a cell.

plasmids - the rings of DNA in bacteria.

pollen - the grains that contain the male reproductive cells of a seed plant.

pollination - the transfer of pollen in a flower from the stamen to the pistil (male to female).

polymerase chain reaction - see PCR.

polymorphisms - the differences in DNA sequences that occur naturally. They are used as genetic markers because researchers can use them to tell apart DNA from different sources.

polyploidy - cells that have extra chromosomes.

population - all the members of a species that live in a particular location.

population genetics - the study of how genetic principles apply to entire generations.

positional cloning - the process of finding the gene for a specific trait by comparing the DNA of people with the trait to the DNA of relatives without the trait.

principle of segregation - the principle, first noted by Gregor Mendel, that explains why children don’t always directly inherit their parents’ characteristics.

probe - a radioactive DNA or RNA molecule used in DNA-RNA or DNA-DNA hybridization trials.

prokaryotes - the living things whose cells do not have nuclei; includes only single-celled bacteria.

propagation - the multiplication of plants.

promoter - a segment of DNA that acts as controlling element in expression of a gene. Marks the place of the beginning of gene transcription.

prophase - the first stage of mitosis or meiosis.

protein - a molecule made up of amino acids linked together. They are the body’s workhorses whose function can be as enzymes, structural components, or signaling molecules.

Punnett Square - a chart that shows all possible genetic outcomes of a mating.

recessive gene - a gene which is hidden by a dominant gene; it must be present on both chromosomes in a pair (one from the father, one from the mother) to show outward signs of the characteristic.

recombinant DNA - the new DNA resulting from combining two or more types of DNA.

recombinant DNA technology - the technique for cutting apart, splicing together and producing pieces of DNA from different sources.

recombination/crossing-over - a process of chromosome exchange during cell division, resulting in new combinations of alleles.

restriction enzyme - an enzyme capable of cutting DNA into fragments.

retrovirus - a cancer-causing virus that transforms cells by altering the function of host-cell genes or by carrying cancer-causing genes from one host to another.

ribosome - the small cellular structure where RNA translates the genetic code into proteins.

RFLP (restriction fragment length polymorphism) - considered to be the most accurate DNA test; it takes several weeks to complete, and is becoming more frequently used in forensics cases.

RNA (ribonucleic acid) - single-stranded nucleic acid (similar to double-stranded DNA) containing the bases adenine (A), cytosine (C), guanine (G), and uracil (U). The different forms include messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), which are all part of making protein.

sense strand - the portion of the DNA double helix that is transcribed during protein synthesis (as opposed to the antisense strand).

sex chromosome - the X or Y chromosome, which determines sex. Females have two X chromosomes in each cell, and males have an X and a Y.

sex-influenced trait - a trait whose expression depends on the sex of the individual organism.

sex-limited trait - a trait expressed in one sex and not in the other.

sex-linked trait - a trait whose gene is located on or linked to the X chromosome.

single-stranded DNA - the result of genes being changed or copied before a cell division; half of the normal two strands that form the double helix.

somatic cell - any cell in the body other than the sex cells.

species - a group of closely related organisms capable of mating and producing fertile offspring.

sperm - the male reproductive cells.

stamen - the male part of a plant, which produces pollen.

telephase - the fourth stage of mitosis where chromosomes uncoil and new nuclear membranes form.

thymine (T) - a base in DNA that always bonds with adenine (A).

transcription - the process by which DNA passes genetic information to RNA. The first step in producing proteins.

transfer RNA (tRNA) - a class of RNA that carries amino acids into ribosomes and bonds with mRNA for protein production.

transformation - a process by which some bacteria can absorb DNA from their surroundings.

transgenic - organisms with inserted genes.

translation - process by which RNA makes proteins.

translocation - a mutation in which a chromosomal piece becomes attached to another chromosome.

uracil (U) - a base in RNA that bonds only with adenine (A).

vector - a DNA molecule into which a gene or DNA segment is inserted by recombinant DNA techniques; a cloning vehicle.

virus - an infectious parasite.

wildtype - the most common phenotype or genotype in a population.

X chromosome - one of the chromosomes that determines sex. Females have two X chromosomes in each somatic cell, and males have one X and one Y chromosome..

Y chromosome - one of the chromosomes that determines sex. Males carry one X chromosome and one Y chromosome in each somatic cell.

zygote - the new cell formed when the male sperm unites with a female egg.