Chapter 24 - Principals of Biology

Linkage group

Term used to identify groups of alleles on a chromosome that tend to be inherited together.

autosomes

Chromosome pairs that are the same between the sexes; in humans, all but the X and Y chromosomes.

sex chromosomes

Chromosomes that differ between the sexes; in humans, these represent the X and Y chromosomes.

sex-linked

Trait controlled by a gene on a sex chromosome; often described as either X-linked or Y-linked.

X-linked

Allele that is located on an X chromosome; not all X-linked genes code for sexual characteristics.

color blindness

Inability to detect specific wavelengths of light associated with color; red-green color blindness is the most common type.

Duchenne muscular dystrophy

Genetic disorder that is characterized by a wasting of muscle tissue; displays an X-linked recessive pattern of inheritance.

fragile x syndrome

Genetic condition caused by an abnormal number of nucleotide repeats; named after the appearance, and not physical characteristics, of the X chromosome.

hemophillia

Genetic disorder that is caused by a deficiency of a clotting factor in the blood.

nondisjunction

Failure of the homologous chromosomes or sister chromatids to separate during either mitosis or meiosis; produces cells with abnormal chromosome numbers.

trisomy

Chromosome condition in which a diploid cell has one more chromosome than normal; designated as 2n + 1.

monosomy

Chromosome condition in which a diploid cell has one less chromosome than normal; designated as 2n −1.

barr body

Dark-staining body in the cell nuclei of female mammals that contains a condensed, inactive X chromosome; named after its discoverer, Murray Barr.

chromosomal mutations

Changes in the physical structure of a chromosome; includes deletions, duplications, inversions, and translocations.

deletion

Change in chromosome structure in which the end of a chromosome breaks off or two simultaneous breaks lead to the loss of an internal segment; often causes abnormalities (e.g., cri du chat syndrome).

duplication

Change in chromosome structure in which a particular segment is present more than once in the same chromosome.

translocation

Movement of a chromosomal segment from one chromosome to another nonhomologous chromosome, leading to abnormalities (e.g., Down syndrome).