Chromosome Mutations

Flashcards about chromosome mutations.

Chromosome mutation

Processes of change in chromosomes.

Two types of Chromosome mutations

Changes in chromosome structure and changes in chromosome number.

Structural mutations

Deletion (deficiency), duplication, translocation, or inversion.

Deletion (deficiency)

Represent a loss in chromosomal material, which may carry one or more genes.

Cri-du Chat syndrome

A genetic disease caused by a deletion of a large part of the short arm of chromosome 5; affected babies have a cat-like cry, are mentally retarded, have a moon face, low birth weight, saddle nose, small mandible and malformed low- set ears.

Duplication (addition)

The presence of a section of a chromosome in excess of the normal amount.

Translocation

Moves a chromosome segment to another position in the genome.

Simple translocation

Involves a single break in the chromosome and the transfer of a broken piece directly onto the end of another.

Shift (intercalary) translocation

Involves three breaks, so that a middle piece from one chromosome is inserted within the break in a nonhomologous chromosome.

Reciprocal translocation (interchanges)

Occur when single breaks in two nonhomologous chromosomes produce an exchange of chromosome segments.

Philadelphia chromosome

Caused by the reciprocal translocation between chromosome 9 and 22; found in about 90% of patients with chronic myelocytic leukaemia (a blood cancer).

Inversion

Involves a break of segment in a chromosome and the rejoining of the segment but after a 180° turn in the segment.

Pericentric inversions

Span the centromere

Paracentric inversions

Do not span the centromeres.

Aneuploidy

The change in number of individual chromosome; chromosomes may be added to or subtracted from normal sets.

Non-disjunction

A mistake in which both chromosomes (or chromatids) pass to the same pole of a cell instead of opposite poles at anaphase during meiosis.

Examples of aneuploid conditions in humans

Klinefelter syndrome (XXY), and Turner syndrome (XO)

Non-disjunction of sex chromosomes

Failure of sex chromosomes in either sex to separate during meiosis in either male or female individuals results in the production of both normal and rare aneuploid gametes

Klinefelter syndrome (XXY)

Sterile males with effeminate tendencies

XYY syndrome

Males affected are sterile and are physically normal but socially deviant

Euploidy

Variation in the number of whole sets (complements) of chromosomes.

Polyploids

Organisms with three or more complement sets of chromosomes.

Monoploids

Have only one set that develops from unfertilised eggs and are very rare.

Human genetic diseases

Those that are inherited by individuals from their parents.

Prenatal diagnostic methods

Used to detect disorders in unborn children.

Amniocentesis

A sample of the amniotic fluid is taken using a syringe and a hypodermic needle around the sixteenth week of pregnancy.

Chorionic villi sampling

A sample of finger like projections called chorionic villi is taken from the chorion, which is the outermost membrane surrounding the foetus.

Human pedigree

A chart of an individual's ancestors used in human genetics to analyze Mendelian inheritance of certain traits, especially of inherited diseases.

Consanguinity

The marriage of related individuals, for example cousins.

Propositus

The individual who first draws the geneticist’s attention to a particular family.

Autosomal traits

Traits are carried on the autosomal chromosomes (not on the sex chromosomes).