Chapter 15 Vocabulary

Barr body

A dense object lying along the inside of the nuclear envelope in cells of female mammals, representing a highly condensed, inactivated X chromosome.

chromosome theory of inheritance

A basic principle in biology stating that genes are located at specific positions (loci) on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns

deletion

(1) A deficiency in a chromosome resulting from the loss of a fragment through breakage. (2) A mutational loss of one or more nucleotide pairs from a gene.

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 with combinations of traits that differ from those found in either parent.

inversion

An aberration in chromosome structure resulting from reattachment of a chromosomal fragment in a reverse orientation to the chromosome from which it originated

linkage map

A genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes.

linked genes

Genes located close enough together on a chromosome that they tend to be 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 diploid cell that has only one copy of a particular chromosome instead of the normal two

nondisjunction

An error in meiosis or mitosis in which members of a pair of homologous chromosomes or a pair of sister chromatids fail to separate properly from each other

recombinant type (recombinant)

An offspring whose phenotype differs from that of the true-breeding P generation parents; also refers to the phenotype itself.

sex-linked gene

A gene located on either sex chromosome. Most sex-linked genes are on the X chromosome and show distinctive patterns of inheritance; there are very few genes on the Y chromosome.

trisomic

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

wild type

The phenotype most commonly observed in natural populations; also refers to the individual with that phenotype.

X-linked gene

A gene located on the X chromosome; such genes show a distinctive pattern of inheritance.

Translocation

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

Polyploid

A chromosomal alteration in which the organism possesses more than two complete chromosome sets. It is a result of an accident in cell division.

Duchenne muscular dystrophy

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

Hemophilia

A human genetic disease caused by a sex-liked recessive allele resulting in the absence of one or more blood-clotting proteins; characterized by excessive bleeding following an injury.

Down syndrome

A human genetic disorder usually caused by the presence of an extra chromosome 21, characterized by developmental delays and heart and other defects that are generally treatable or non-life-threatening

aneuploidy

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

Parental type

An offspring with a phenotype that matches one of the true-breeding parental (P generation) phenotypes