AP Biology: Chapter 15

chromosome theory of inheritance

genes have specific loci along chromosomes, and these chromosomes undergo segregation and independent assortment

wild type

the phenotype for a character most commonly observed in populations

sex-linked gene

a gene located on either sex chromosome

Duchenne muscular dystrophy

a sex-linked disorder characterized by a progressive weakening of the muscles and loss of coordination

hemophilia

a sex-linked recessive disorder defined by the absence of one or more of the proteins required for blood clotting

Barr body

the inactive X in each cell of a female condenses into a compact object, lies along the inside of the nuclear envelope

linked genes

genes located on the same chromosome that tend to be inherited together in genetic crosses

genetic recombination

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

parental types

offspring which inherit a phenotype that matches one of the parental phenotypes

recombinant types

offspring which with a phenotype different from each parent

crossing over

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

genetic map

an ordered list of the genetic loci along a particular chromosome

linkage map

a genetic map based on recombination frequencies

map units

one is equal to a 1% recombination frequency

cytogenetic maps

locate genes with respect to chromosomal features

nondisjunction

the members of a pair of homologous chromosomes do not move apart properly during meiosis I or sister chromatids fail to separate during meiosis II

aneuploidy

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

monosomic

a cell that has only one copy of a particular chromosome instead of two

trisomic

a diploid cell with three copies of a particular chromosome instead of two

polyploidy

the chromosomal alteration in which the organism has more than two complete chromosome sets in all somatic cells

deletion

occurs when a chromosomal fragment is lost

duplication

occurs when the deleted fragment becomes attached as an extra segment to a sister chromatid

inversion

occurs when a chromosomal fragment reattaches to the original chromosome but in the reverse orientation

translocation

occurs when the fragment joins a non-homologous chromosome, rearranging along the chromosome

Down syndrome

an aneuploid condition resulting from an extra chromosome 21, so that each body cell has a total of 47 chromosomes

genomic imprinting

variation in phenotype depending on whether an allele is inherited from the male or female parent