AP BIO CH 15

aneuploidy

A chromosomal aberration in which one or more chromosomes are present in extra copies or are deficient in number.

Barr body

A dense object lying along the inside of the nuclear envelope in female mammalian cells, representing an inactivated X chromosome.

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.

crossing over

The reciprocal exchange of genetic material between nonsister chromatids during prophase I of meiosis

cytologenetic map

Chart of a chromosome that locates genes with respect to chromosomal features.

deletion

(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage.

deletion

(2) A mutational loss of one or more nucleotide pairs from a gene

Down syndrome

A human genetic disease caused by presence of an extra chromosome 21; characterized by mental retardation and heart and respiratory defects.

Duchenne muscular dystrophy

A human genetic disease caused by a sex-linked recessive allele; characterized by progressive weakening and a loss of muscle tissue.

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.

genetic map

An ordered list of genetic loci (genes or other genetic markers) along a chromosome.

genetic recombination

General term for the production of offspring that combine traits of the two parents.

genomic imprinting

Phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent.

hemophilia

A human genetic disease caused by a sex-linked recessive allele; characterized by excessive bleeding following injury.

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.

linked genes

Genes located close enough together on a chromosome to be usually inherited together.

map unit

A unit of measurement of the distance between genes. One map unit is equivalent to a 1% recombination frequency.

monosomic

Referring to a cell that has only one copy of a particular chromosome, instead of the normal two.

polyploidy

A chromosomal alteration in which the organism possesses more than two complete chromosome sets.

recombinant

An offspring whose phenotype differs from that of the parents; also called recombinant type.

sex-linked gene

A gene located on a sex chromosome.

translocation

1) An aberration in chromosome structure resulting from attachment of a chromosomal fragment to a nonhomologous chromosome.

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.

translocation

(3) The transport of organic nutrients in the phloem of vascular plants.

trisomic

Referring to a cell that has three copies of a particular chromosome, instead of the normal two.

wild type

An individual with the normal (most common) phenotype.