| A | B |
|---|
| Histones | A small protein with a high proportion of positively charged amino acids that binds to the negatively charged DNA and plays a key role in its chromatin structure |
| Nucleosome | The basic, bead-like unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histones |
| Heterochromatin | Non-transcribed eukaryotic chromatin that is so highly compacted that it is visible with a light microscope during interphase |
| Euchromatin | The more open, unraveled form of eukaryotic chromatin that is available for transcription |
| Repetitive DNA | Nucleotide sequences, usually noncoding, that are resent in many copies in a eukaryotic genome. The repeated units may be short and arranged tandemly or long and dispersed in the genome |
| Satellite DNA | portion of DNA in eukaryotes whose density differs from that of the majority of DNA and that consists of short, repeating sequences of nucleotide pairs |
| Alu elements | In humans, a set of closely related genetic sequences, each about 300 base pairs long |
| Multigene family | A collection of gene with similar or identical sequences, presumably of common origin |
| Pseudogene | A DNA segment very similar to a real gene but which does not yield a functional product; a gene that has become inactivated in a particular species because of mutation |
| Gene amplification | The process by which the number of copies of a gene is increased in certain cells; in humans it is most often seen in malignant cells |
| Retrotransposons | A transposable element that moves within a genome by means of an RNA intermediate, a transcript of the retrotransposon DNA |
| Immunoglobulins | Any of the class of proteins that function as antibodies. Immunoglobulins are divided into five major classes that differ in their distribution in the body and antigen disposal activities |
| differentiation | divergence in form and function as cells become specialized during and organism's development |
| DNA methylation | attachment of methyl groups to DNA bases after DNA is synthesized |
| genomic imprinting | methylation permanently turns off either the maternal or paternal allele of certain genes at the start of development |
| histone acetylation | attachment of acetyl groups to certain amino acids of histone proteins |
| control elements | segments of noncoding DNA that help regulate transcription of a gene by binding proteins (transcription factors) |
| enhancers | DNA sequence that recognizes certain transcription factors that can stimulate transcription of nearby genes |
| activator | transcription factor that binds to an enhancer and stimulates transcription of a gene |
| DNA-binding domain | part of a transcription factor's 3D structure that binds selectively to DNA |
| alternative splicing | different mRNA molecules are produces from the same primary transcript depending on which RNA segments are treated as exons and which as introns |
| proteasomes | giant protein complexes that recognize the ubiquintin and degrade the tagged protein |
| oncogenes | a gene found in viruses or as part of the normal genome that is involved in triggering cancerous characteristics |
| proto-oncogenes | a normal cellular gene corresponding to an oncogene; a gene with potential to cause cancer, but requires some alteration to become an oncogene |
| Tumor suppressor geme | A gene whose protein products inhibits cell division, thereby preventing uncontrolled cell growth (Cancer) |
| Ras Gene | A gene that codes for Ras protein, a G-protein that rlays a growth signal from a growth factor rceptor on the plasma membrane to a cascade of protein kinase that ultimately results in the stimulatio of the cel cycle Many ras oncogenes have a point mutation that leads to a hyperative version of the Ras protein that can lead to excessive cell divistion. |
| p53 gene | The "guardian angle of the genome", a gene that is expressed bwhen a cell;s DNA is damaged. Its product, p53 protein, functions as a transcription factor for several genes. |
| Maternal effect genes | A gene that, when mutant in the mother, results in a mutant phenotype in the offspring, regardless of the genotype. |
| egg-polarity genes | Another name for a maternal effect gene, a gene that helps control the orientation (polarity) of the egg. |
| morphogens | A substance, such a Bicoid protein, that provides positional information in the form of a concentration gradient along an embryonic axis. |
| Segmentation genes | A gene of the embryo that directs the actual formation of segments after the embryo's axes are defined. |
| Homeotic genes | Any of the genes that control the overall body plan of animals and plants by controlling the developmental fate of group cells |
| homeobox | A 180-nucleotide sequence within homeotic genes and some other developmental genes that is widely conserved in animals. |
| Apoptosis | The changes that occur within a cell as it undergoes programmed cell death, which is brought about by signals that trigger the activation cascade of suicide proteins in the celll destined to die. |
| Chimeras | An organism with a mixture of genetically different cells. |
| Organ-identity genes | Plant homeotic genes that use positional information to determine which emerging leaves develop into which types of floral organs. |
