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Definition
| Alternative versions of a gene that produce distinguishable phenotypic effects. |
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Definition
| A technique of prenatal diagnosis in which amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus. |
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Term
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Definition
| In genetics, an individual who is heterozygous at a given genetic locus, with one normal allele and one potentially harmful recessive allele. The heterozygote is phenotypically normal for the character determined by the gene but can pass on the harmful allele to offspring. |
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Term
| chorionic villus sampling (CVS) |
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Definition
| A technique of prenatal diagnosis in which a small sample of the fetal portion of the placenta is removed and analyzed to detect certain genetic and congenital defects in the fetus. |
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Definition
| The situation in which the phenotypes of both alleles are exhibited in the heterozygote. |
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Term
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Definition
| The situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable. |
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Term
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Definition
| An organism that is heterozygous with respect to two genes of interest. All the offspring from a cross between parents doubly homozygous for different alleles are dihybrids. For example, parents of genotypes AABB and aabb produce a dihybrid of genotype AaBb. |
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Term
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Definition
| A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited. |
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Term
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Definition
| The genetic makeup, or set of alleles, of an organism. |
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Term
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Definition
| Having two different alleles for a given gene. |
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Term
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Definition
| Having two identical alleles for a given gene. |
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Term
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Definition
| The situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele. |
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Term
| law of independent assortment |
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Definition
| Mendel’s second law, stating that each pair of alleles segregates independently during gamete formation; applies when genes for two characters are located on different pairs of homologous chromosomes. |
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Term
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Definition
| Mendel’s first law, stating that each allele in a pair separates into a different gamete during gamete formation. |
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Term
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Definition
| An organism that is heterozygous with respect to a single gene of interest. All the offspring from a cross between parents homozygous for different alleles. For example, parents of genotypes AA and aa produce a monohybrid of genotype Aa. |
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Term
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Definition
| Referring to a phenotypic character that is influenced by multiple genes and environmental factors. |
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Term
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Definition
| A diagram of a family tree showing the occurrence of heritable characters in parents and offspring over multiple generations. |
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Term
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Definition
| The physical and physiological traits of an organism, that are determined by its genetic makeup. |
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Term
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Definition
| The ability of a single gene to have multiple effects. |
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Term
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Definition
| An additive effect of two or more gene loci on a single phenotypic character. |
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Term
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Definition
| A heritable feature that varies continuously over a range rather than in an either-or fashion. |
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Term
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Definition
| Breeding of an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype. The ratio of phenotypes in the offspring determines the unknown genotype. |
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Term
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Definition
| A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number. |
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Term
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Definition
| A dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome. |
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Term
| chromosome theory of inheritance |
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Definition
| A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns. |
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Term
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Definition
| Chart of a chromosome that locates genes with respect to chromosomal features. |
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Term
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Definition
| A deficiency in a chromosome resulting from the loss of a fragment through breakage. |
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Term
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Definition
| An aberration in chromosome structure due to fusion with a fragment from a homologous chromosome, such that a portion of a chromosome is duplicated. |
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Term
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Definition
| An ordered list of genetic loci (genes or other genetic markers) along a chromosome. |
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Term
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Definition
| General term for the production of offspring that combine traits of the two parents. |
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Term
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Definition
| Phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent. |
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Term
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Definition
| An aberration in chromosome structure resulting from reattachment in a reverse orientation of a chromosomal fragment to the chromosome from which the fragment originated. |
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Term
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Definition
| A genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes. |
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Term
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Definition
| Genes located close enough together on a chromosome to be usually inherited together. |
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Term
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Definition
| A unit of measurement of the distance between genes. One map unit is equivalent to a 1% recombination frequency. |
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Term
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Definition
| Referring to a cell that has only one copy of a particular chromosome, instead of the normal two. |
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Term
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Definition
| An error in meiosis or mitosis, in which both members of a pair of homologous chromosomes or both sister chromatids fail to move apart properly. |
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Term
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Definition
| A chromosomal alteration in which the organism possesses more than two complete chromosome sets. |
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Definition
| A gene located on a sex chromosome. |
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Term
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Definition
| An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome. |
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Term
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Definition
| Referring to a cell that has three copies of a particular chromosome, instead of the normal two. |
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