AP Bio Chapter 15

chromosomal basis of inheritance

genetic recombination

general term for the production of offspring with combinations of traits that differ from those found in either parent

map unit

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

X-linked gene

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

aneuploidy

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

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.

polyploidy

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

crossing over

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

genomic imprinting

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

parental type

An offspring with a phenotype that matches one of the true-breeding parental (P generation) phenotypes; also refers to the phenotype itself.

recombinant type

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.

Duchenne muscular dystrophy

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

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.

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.

inversion

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

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.

translocation

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

linkage map

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

Down syndrome

A human genetic disease 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.

linked genes

Genes located close enough together on a chromosome that they tend to be inherited together.

hemophilia

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

trisomic

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

genetic map

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

wild type

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

monosomic

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

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.