Essentials of Genetics – Chapter 6: Chromosome Mutations

Vocabulary flashcards cover key terms and definitions related to chromosome number variations, structural aberrations, their origins, and associated human syndromes presented in Chapter 6.

Chromosome mutation (chromosomal aberration)

Any change in chromosome number or structure that can lead to phenotypic variation or lethality.

Aneuploidy

Condition in which an organism gains or loses one or more individual chromosomes but not a complete set (2n ± x).

Monosomy

Form of aneuploidy involving the loss of a single chromosome (2n − 1).

Trisomy

Form of aneuploidy involving the gain of a single chromosome (2n + 1).

Polyploidy

Condition in which more (or fewer) than two complete haploid sets of chromosomes are present (e.g., 3n, 4n).

Monoploidy

Presence of only one haploid set of chromosomes (n) in an otherwise diploid organism.

Triploidy

Polyploid state with three complete sets of chromosomes (3n).

Tetraploidy

Polyploid state with four complete sets of chromosomes (4n).

Autopolyploidy

Polyploidy arising from duplication of the same species’ genome (multiple identical chromosome sets).

Allopolyploidy (Amphidiploidy)

Polyploidy resulting from the combination of chromosome sets from two different species via hybridization.

Nondisjunction

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis, producing gametes with abnormal chromosome numbers.

Turner syndrome

Human monosomy condition with karyotype 45,X; characterized by short stature and infertility.

Klinefelter syndrome

Human aneuploidy condition with karyotype 47,XXY; leads to male infertility and some feminine characteristics.

Down syndrome (Trisomy 21)

Aneuploid condition (47,21+) producing characteristic facial features, cognitive disability, and increased leukemia risk.

Maternal age effect (Down syndrome)

The incidence of trisomy 21 increases substantially in pregnancies of women older than ~45 years.

Deletion (Deficiency)

Chromosomal mutation in which a segment is missing; can be terminal or intercalary.

Terminal deletion

Loss of a chromosome segment from the end of a chromosome arm.

Intercalary deletion

Loss of an internal chromosome segment; the centromere-containing part is retained.

Cri du chat syndrome

Segmental deletion of the short arm of chromosome 5 (46,5p−) causing a cat-like cry and intellectual disability.

Duplication

Mutation in which a chromosome segment is repeated, often due to replication errors.

Gene redundancy

Presence of multiple copies of the same gene within a genome, often produced by duplication.

Copy Number Variant (CNV)

Region of DNA in which the number of copies varies between individuals; linked to both normal variation and disease.

Inversion

Chromosome aberration in which a segment is reversed 180° within the chromosome without loss of genetic material.

Paracentric inversion

Inversion that does not include the centromere.

Pericentric inversion

Inversion that includes the centromere.

Translocation

Movement of a chromosome segment to a non-homologous chromosome or to a new location on the same chromosome.

Reciprocal translocation

Exchange of segments between two non-homologous chromosomes with no net loss of genetic material.

Robertsonian translocation

Fusion of the long arms of two acrocentric chromosomes, producing a large metacentric chromosome and a small fragment.

Familial Down syndrome

Heritable form of trisomy 21 caused by a 14/21 Robertsonian translocation; parent is a translocation carrier (45 chromosomes).

Fragile site

Heritable, unstained gap on a metaphase chromosome prone to breakage under certain culture conditions.

Fragile-X syndrome (FXS)

Most common inherited intellectual disability, associated with a folate-sensitive fragile site on the X chromosome.

Chromosome aberration breakage

Structural changes (deletions, duplications, inversions, translocations) initiated by chromosome breaks from spontaneous events or exposure to chemicals/radiation.

Disomy

Normal diploid state with two copies of each homologous chromosome (2n).

Tetrasomy

Aneuploid state with an extra pair of a particular chromosome (2n + 2).

Pentaploidy

Polyploid state with five complete sets of chromosomes (5n).

Autotriploid formation

Arises when a diploid gamete (due to nondisjunction) is fertilized by a normal haploid gamete, or when two sperm fertilize one ovum.

Phenotypic variation (chromosome level)

Observable differences in traits that result from changes in chromosome number or structure.

Gene evolution by duplication

Process proposed by Susumu Ohno (1970) in which duplicated genes accumulate mutations leading to new functions and increased organismal fitness.

Centromere

Chromosome region required for proper segregation; location distinguishes paracentric vs. pericentric inversions.