A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.
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Barr body
A dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome.
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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.
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crossing over
The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis
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cytologenetic map
Chart of a chromosome that locates genes with respect to chromosomal features.
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deletion
(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage.
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deletion
(2) A mutational loss of one or more nucleotide pairs from a gene
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Down syndrome
A human genetic disease caused by presence of an extra chromosome 21; characterized by mental retardation and heart and respiratory defects.
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Duchenne muscular dystrophy
A human genetic disease caused by a sex-linked recessive allele; characterized by progressive weakening and a loss of muscle tissue.
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duplication
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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genetic map
An ordered list of genetic loci (genes or other genetic markers) along a chromosome.
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genetic recombination
General term for the production of offspring that combine traits of the two parents.
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genomic imprinting
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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hemophilia
A human genetic disease caused by a sex-linked recessive allele; characterized by excessive bleeding following injury.
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inversion
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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linked genes
Genes located close enough together on a chromosome to be usually inherited together.
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map unit
A unit of measurement of the distance between genes. One map unit is equivalent to a 1% recombination frequency.
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monosomic
Referring to a cell that has only one copy of a particular chromosome, instead of the normal two.
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polyploidy
A chromosomal alteration in which the organism possesses more than two complete chromosome sets.
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recombinant
An offspring whose phenotype differs from that of the parents; also called recombinant type.
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sex-linked gene
A gene located on a sex chromosome.
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translocation
1) An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome.
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translocation
(2) During protein synthesis, the third stage in the elongation cycle when the RNA carrying the growing polypeptide moves from the A site to the P site on the ribosome.
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translocation
(3) The transport of organic nutrients in the phloem of vascular plants.
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trisomic
Referring to a cell that has three copies of a particular chromosome, instead of the normal two.
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wild type
An individual with the normal (most common) phenotype.
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