Unit 5 ch. 12

Linked genes

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.

Crossing over

The reciprocal exchange of genetic material between nonsister chromatids during prophase 1 of meiosis.

Wild type

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

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

X-linked genes

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

Linked genes

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

Linkage map

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

Genetic reombination

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

Genetic Map

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

Parental types

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

Polyploidy

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

Recombinant types (recombinants)

A chromosome created when crossing over combined DNA from two parents into a single chromosome.

Nondisjunction

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

Aneuploidy

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

Monosomic

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

Trisomic

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

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 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 form which it originated.

Translocation

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