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| chromosome theory of inheritance | a basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns |
| wild type | an individual with the normal phenotype |
| sex-linked genes | a gene located on a sex chromosome |
| linked genes | genes that are located on the same chromosome |
| genetic recombination | the general term for the production of offspring with new combinations of traits inherited from the two parents |
| parental types | offspring with a phenotype that matches one of the parental phenotypes |
| recombinants | an offspring whose phenotype differs from that of the parents |
| genetic map | an ordered list of genetic loci (genes or other genetic markers) along a chrmosome |
| linkage map | a genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes |
| map units | a measurement of the distance between genes; one map unit is equivalent to a 1% recombination frequency |
| cytological maps | charts of chromosomes that locate genes with respect to chromosomal features |
| Duchenne muscular dystrophy | a human genetic disease caused by a sex-linked recessive allele; characterized by progressive weakening and loss of muscle tissue |
| hemophilia | a human genetic disease caused by a sex-linked recessive allele; characterized by excessive bleeding following injury |
| Barr body | a dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome |
| nondisjunction | an accident of meiosis or mitosis, in which the members of a pair of homologous chromosomes or sister chromatids fail to move apart properly |
| aneuploidy | a chromosomal aberration in which certain chromosomes are present in extra copies or are deficient in number |
| trisomic | a chromosomal condition in which a particular cell has an extra copy of one chromosome, instead of the normal two |
| monosomic | a chromosomal condition in which a particular cell has only one copy of a chromosome, instead of the normal two |
| polyploidy | a chromosomal alteration in which the organism posses more than two complete chromosome sets |
| deletion | a deficiency in a chromosome resulting from the loss of a fragment through breakage; a mutational loss of one or more nucleotide pairs from a gene |
| inversion | an aberration in chromosome structure resulting from an error in meiosis or from mutagens; specifically, reattachment of a chromosomal fragment to the chromosome from which the fragment originated, but in a reverse orientation |
| translocation | an aberration in chromosome structure resulting from an error in meiosis or from mutagens; specifically, attachment of a chromosomal fragment to a nonhomologous chromosome |
| Down syndrome | a human genetic disease resulting from having an extra chromosome 21, characterized by mental retardation and heart and respiratory defects |
| genomic imprinting | the parental effect on gene expression whereby identical alleles have different effects on offspring, depending on whether they arrive in the zygote via the ovum or via the sperm |
| fragile X syndrome | a hereditary mental disorder, partially explained by genomic imprinting and the addition of nucleotides to a triplet repeat near the end of an X chromosome |
