Genetics Exam 2 Vocab

Pedigree

Pictorial representation of a family history, essentially a family tree that outlines the inheritance of one or more characteristics

Proband

The person from whom the pedigree is initiated

Consanguinity

Mating between closely related people

Genetic Mosaic

Condition in which regions of tissue within a single individual have different chromosome constitutions

Chromosome mutation

Variations in the number and structure of chromosomes; often affects many genes and has large phenotypic effects

Metacentric chromosome

Chromosome in which the two chromosome arms are approximately the same length

Submetacentric chromosome

Chromosome in which the centromere is displaced toward one end, producing a short arm and a long arm

Acrocentric chromosome

Chromosome in which the centromere is near one end, producing a long arm at one end and a knob, or satellite, at the other end

Telocentric chromosome

Chromosome in which the centromere is at or very near one end

Chromosome rearrangement

Chromosome mutations that change the structures of individual chromosomes

Chromosome duplication

Mutation that doubles a segment of a chromosome

Tandem duplication

Chromosome rearrangement in which a duplicated chromosome segment is adjacent to the original segment

Displaced duplication

Chromosome rearrangement in which the duplicated segment is some distance from the original segment, either on the same chromosome or on a different one

Reverse duplication

Duplication of a chromosome segment in which the sequence of the duplicated segment is inverted relative to the sequence of the original segment

Segmental duplications

Duplicated chromosome segments larger than 1000 bp

Unequal crossing over

Misalignment of the two DNA molecules during crossing over, resulting in one DNA molecule with an insertion and the other with a deletion

Chromosome deletion

Loss of a chromosome segment

Pseudodominance

Expression of a normally recessive allele due to a deletion on the homologous chromosome

Haploinsufficient gene

Gene that must be present in two copies for normal function. If one copy of the gene is missing, a mutant phenotype is produced

Chromosome inversion

Rearrangement in which a segment of a chromosome has been inverted 180 degrees

Paracentric inversion

Chromosome inversion that does not include the centromere in the inverted region

Pericentric inversion

Chromosome inversion that includes the centromere in the inverted region

Position effect

Dependence of the expression of a gene on the gene’s location in the genome

Dicentric chromosome

Chromatid that has two centromeres; produced when crossing over takes place within a paracentric inversion. The two centromeres are frequently pulled toward opposite poles in mitosis or meiosis, breaking the chromosome

Acentric chromatid

Chromatid that lacks a centromere; produced when crossing over takes place within a paracentric inversion. It does not attach to a spindle microtubule and does not segregate in meiosis or mitosis, so it is usually lost after one or more rounds of cell division

Dicentric bridge

Structure produced when the two centromeres of a dicentric chromatid are pulled toward opposite poles, stretching the dicentric chromosome across the center of the nucleus. Eventually, it breaks as the two centromeres are pulled farther apart

Translocation

(1) Movement of genetic material between nonhomologous chromosomes or within the same chromosome. (2) Movement of a ribosome along mRNA in the course of translation

Nonreciprocal translocation

Movement of a chromosome segment to a nonhomologous chromosome or chromosomal region without any (or with unequal) reciprocal exchange of segments

Reciprocal translocation

Reciprocal exchange of segments between two nonhomologous chromosomes

Robertsonian translocation

Translocation in which the long arms of two acrocentric chromosomes become joined to a common centromere, generating a metacentric chromosome with two long arms and another chromosome with two very short arms

Alternate segregation

Type of segregation that takes place in a heterozygote for a translocation. If the original, nontranslocated chromosomes are N ₁ and N ₂ and the chromosomes containing the translocated segments are T ₁ and T ₂ , then alternate segregation takes place when N ₁ and N ₂ move toward one pole and T ₁ and T ₂ move toward the opposite pole

Adjacent-1 segregation

Type of segregation that takes place in a heterozygote for a translocation. If the original, nontranslocated chromosomes are N ₁ and N ₂ and the chromosomes containing the translocated segments are T ₁ and T ₂ , then adjacent-1 segregation takes place when N ₁ and T ₂ move toward one pole and T ₁ and N ₂ move toward the opposite pole

Adjacent-2 segregation

Type of segregation that takes place in a heterozygote for a translocation. If the original, nontranslocated chromosomes are N ₁ and N ₂ and the chromosomes containing the translocated segments are T ₁ and T ₂ , then adjacent-2 segregation takes place when N ₁ and T ₁ move toward one pole and T ₂ and N ₂ move toward the opposite pole

Fragile site

Constriction or gap that appears at a particular location on a chromosome when cells are cultured under special conditions

Fragile-X syndrome

A form of X-linked intellectual disability that appears primarily in males; associated with a fragile site that results from an expanding trinucleotide repeat

Copy-number variation (CNV)

Difference among individual organisms in the number of copies of any large DNA sequence (larger than 1000 bp)

Structural variants

Collective term for chromosome rearrangements and copy-number variations