8. Variation in Chromosome Structure and Number Flashcards
genetic differences among members of the same species or among different species.
Genetic Variation
genetic variation in a population that involves the occurrence of two or more different alleles for a particular gene.
Allelic Variation
a scientist who studies chromosomes under the microscope.
Cytogeneticist
describes a chromosome with the centromere near the middle.
Metacentric
describes a chromosome in which the centromere is slightly off center.
Submetacentric
describes a chromosome with the centromere significantly off center, but not at the end.
Acrocentric
describes a chromosome with its centromere at one end.
Telocentric
a photographic representation of all the chromosomes within a cell. It reveals how many chromosomes are found within an actively dividing somatic cell.
Karyotype
the chromosomal banding pattern that is observed when the chromosomes have been treated with the chemical called Giemsa stain.
G Bands
condition in which a segment of DNA is missing.
Deletion
condition in which a segment of chromosomal material is missing.
Deficiency
the repetition of a segment of DNA more than once within a chromosome and/or within a genome.
Duplication
a change in the orientation of genetic material along a chromosome such that a segment is flipped or reversed from the normal order.
Inversion
(1) rearrangement in which one segment of a chromosome breaks off and becomes attached to a different chromosome or a different part of the same chromosome; (2) event that occurs when a ribosome moves from one codon in an mRNA to the next codon.
Translocation
rearrangement in which one piece of a chromosome becomes attached to a different chromosome.
Simple Translocation
rearrangment in which two different chromosomes exchange pieces.
Reciprocal Translocation
deletion in which a segment is lost from the end of a linear chromosome.
Terminal Deletion
deletion in which an internal segment is lost from a linear chromosome.
Interstitial Deletion
short DNA sequences that occur many times within a species’ genome.
Repetitive Sequences
recombination that occurs at homologous sites within chromosomes, where the sites are not alleles of the same gene. Such misaligned crossovers are often due to the occurrence of repetitive sequences.
Nonallelic Homologous Recombination
an increase in the copy number of a gene. Can lead to the evolution of gene families.
Gene Duplication
two or more genes within a single species that are similar to each other because they were derived from the same ancestral gene.
Gene Family
describes attributes that are the result of homology. In the case of genes, this term describes two genes that are derived from the same ancestral gene.
Homologous
homologous genes within a single species that constitute a gene family.
Paralogs
a type of structural variation in which a segment of DNA that is 1000 bp or more in length commonly exhibits copy number differences among members of the same species.
Copy Number Variation (CNV)
a duplication in which a small segment of a chromosome has more than one copy of the same gene.
Segmental Duplication
a hybridization technique to determine if cells (e.g., cancer cells) have changes in chromosome structure, such as deletions or duplications.
Comparative Genomic Hybridization (CGH)
the phenomenon in which two single-stranded DNA molecules from different sources bind to form a hybrid molecule.
Hybridization
an inversion in which the centromere is located within the inverted region of the chromosome.
Pericentric Inversion
an inversion in which the centromere is found outside the inverted region.
Paracentric Inversion
a change in phenotype that occurs when the location of a gene changes from one chromosomal site to a different one.
Position Effect
a diploid individual that carries one normal chromosome and a homologous chromosome with an inversion.
Inversion Heterozygote
the loop structure that is formed when the homologous chromosomes of an inversion heterozygote attempt to align themselves (i.e., synapse) during meiosis.
Inversion Loop
a fragment of a chromosome that lacks a centromere.
Acentric Fragment
describes a chromosome with two centromeres.
Dicentric
the region between the two centromeres in a dicentric chromosome.
Dicentric Bridge
specialized repeated sequences found at the ends of eukaryotic chromosomes.
Telomeres
a translocation, such as a reciprocal translocation, in which the total amount of genetic material remains normal or nearly normal.
Balanced Translocation
a translocation in which a cell has too much or too little genetic material compared with a normal cell.
Unbalanced Translocation
the structure produced when two telocentric chromosomes fuse at their short arms.
Robertsonian Translocation
the structure that is formed when chromosomes that have undergone a reciprocal translocation attempt to synapse during meiosis. This structure contains two normal (nontranslocated) chromosomes and two translocated chromosomes. A total of eight chromatids are found within the cross.
Translocation Cross
condition in which an individual has a lowered fertility.
Semisterility
describes an organism in which the chromosome number is an exact multiple of a chromosome set.
Euploid
describes an organism or cell with three sets of chromosomes.
Triploid
describes an organism or cell with four sets of chromosomes (i.e., 4n).
Tetraploid
describes an organism or cell with three or more sets of chromosomes.
Polyploid
not euploid. Refers to a variation in chromosome number such that the total number of chromosomes is not an exact multiple of a set (or of the number n).
Aneuploid
describes a diploid cell or organism with one extra chromosome (i.e., 2n + 1).
Trisomic
describes a diploid cell or organism that is missing a chromosome (i.e., 2n − 1).
Monosomic
event in which chromosomes do not segregate properly during mitosis or meiosis.
Nondisjunction
describes a species, such as certain bees, in which one sex is haploid (e.g., male) and the other sex is diploid (e.g., female).
Haploidiploid
in a diploid individual, the phenomenon in which certain cells of the body are polyploid.
Endoplolyploidy
aggregation of chromosomes found in certain cells, such as Drosophila salivary cells, in which homologous chromosomes have synapsed and replicated many times and the copies lie side by side.
Polytene Chromosome
the central point where the chromosomes of a polytene chromosome aggregate.
Chromocenter
the event in which chromosomes do not segregate properly during meiosis.
Meiotic Nondisjunction
an event in which chromosomes do not segregate properly during mitosis.
Mitotic Nondisjunction
describes an organism that contains sets of chromosomes from two or more different species.
Alloploid
event in which all of the chromosomes fail to segregate properly during meiosis or mitosis and remain in one of the two daughter cells.
Complete Nondisjunction
condition in which the cells of part of an organism differ genetically from those of the rest of the organism.
Mosaicism
a polyploid produced within a single species due to nondisjunction.
Autopolyploid
describes an organism that contains one set of chromosomes from two different species.
Allodiploid
describes an organism that contains two (or more) sets of chromosomes from two (or more) species.
Allopolypoid
describes an organism that contains two sets of chromosomes from two different species.
Allotetraploid
