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a segment of DNA that codes for specific gene products


a different form of a particular gene


the genetic makeup of an organism


a visible observation, or tested


sex cells (sperm and egg)


during metaphase, the chromosomes make an ordered display according to their position and size


when both alleles of a particular gene on a pair of homologous chromosomes are identical


when two alleles of a certain gene on a pair of homologous chromosomes are not identical

dominant trait

an allele that is observable

recessive trait

an allele that is hidden


the percentage of individuals with a specific genotype who also express the expected phenotype


agents known to increase the frequency of mutations


the extent of variation in phenotype associated with a particular genotype

base-pair substitution

mutation in which one base pair is replaced by another. Sometimes change the amino acid sequence

silent substitution

a mutation in which a base pair is replaced by another, but does not change the amino acid sequence

frame-shift substitution

a mutation that involves the insertion or deletion of one or more base pairs to the DNA molecule. Greatly alters the amino acid sequence

spontaneous mutation

mutation that occurs in absence of exposure to known mutagens

germline mutation

a mechanism by which a child can inherit a genetic disease even though the parents do not express the disease. The mechanism is believed to involve a mutation during the embryonic development of the parent germ cell

mutational hotspots

certain areas of chromosomes that have a particularly high mutation rate


cells that have a multiple of the normal number of chromosomes


have only one member of each chromosome pair


have both member of each chromosome pair. Normal is 23 pairs


when a euploid cell has more than the diploid number of chromosomes


a somatic cell that does not contain a multiple of 23 chromosomes


has three copies of one chromosome


has only one copy of a given chromosome in a diploid cell


an error in which homologous chromosomes or sister chromatids fail to separate normally during meiosis or mitosis


caused by broken chromosomes and loss of DNA


are a form of chromosomal abberation. Have less serious complications than deletions


the occurrence of two breaks in a chromosome followed by the reinsertion of the missing fragment at its original site, but in an inverted order


the interchanging of genetic material between nonhomologous chromosomes

fragile sites

an area where it is more prone to develop breaks and gaps when cultured in a folate-deficient medium


a trait normally found on the sex chromosomes


a trait normally found on the x chromosome


an individual that has a diseased gene but is phenotypically normal


the normal separation and migration of chromosomes during cell division


abnormal gene

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