ch 8 variation in chromosome structure & number Flashcards
genetic variation
genetic differences among members of the same species or among different species
allelic variation
genetic variation in a population that involves the occurrence of two or more different alleles for a particular gene
cytogeneticist
a scientist who studies chromosomes under the microscope
metacentric
describes a chromosome with the centromere near the middle
submetacentric
describes a chromosome in which the centromere is slightly off the center
acrocentric
describes a chromosome with the centromere significantly off center, but not at the end
telocentric
describes a chromosome with its centromere at one end
G bands
the chromosomal banding pattern that is observed when the chromosomes have been treated with the chemical called Giemsa stain
deletion
condition in which a segment of DNA is missing
deficiency
condition in which a segment of chromosomal material is missing
duplication
the repetition of a segment of DNA more than once within a chromosome and/or within a genome
inversion
a change in the orientation of genetic material along a chromosome such that a segment is flipped or reversed from the normal order
translocation
- rearrangement in which one segment of a chromosome breaks off and becomes attached to a different part of the same chromosome
- event that occurs when a ribosome moves from one codon in an mRNA to the next codon
simple translocation
rearrangement in which one piece of a chromosome becomes attached to a different chromosome
reciprocal translocation
rearrangement in which two different chromosomes exchange pieces
terminal deletion
(also called see terminal deficiency) deletion in which a segment is lost from the end of a linear chromosome
interstitial deletion
(also called interstitial deficiency) deletion in which an internal segment is lost from a linear chromosome
repetitive sequences
short DNA sequences that occur many times within a species’ genome
nonallelic homologous recombination
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 spequences
gene duplication
an increase in the copy number of a gene; can lead to the evolution of gene families
gene family
two or more genes within a single species that are similar to each other because they were derived from the same ancestral gene
copy number variation (CNV)
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
segmental duplication
a duplication in which a small segment of a chromosome has more than one copy if the same gene
comparative genomic hybridization (CGH)
a hybridization technique to determine if cells have changes in chromosome structure, such as deletions or duplications
pericentric inversion
an inversion in which the centromere is located within the inverted region of the chromosome
paracentric inversion
an inversion in which the centromere is found outside the inverted region
position effect
a change in phenotype that occurs when the location of a gene changes from one chromosomal site to a different one
inversion heterozygote
a diploid individual that carries one normal chromosome and a homologous chromosome with an inversion
inversion loop
the loop structure that is formed when the homologous chromosomes of an inversion heterozygote attempt to align themselves
acentric fragment
a fragment of chromosomes that lacks a centromere
dicentric
describes a chromosome with two centromeres
dicentric bridge
the region between the two centromeres in a dicentric chromosomes
telomeres
specialized repeated sequences found at the ends of eukaryotic chromosomes
balanced translocation
a translocation, such as a reciprocal translocation, in which the total amount of genetic material remains normal or nearly normal
unbalanced translocation
a translocation in which a cell has too much or too little genetic material compared with a normal cell
robertsonian translocation
the structure produced when two telocentric chromosomes fuse at their short arms
translocation cross
the structure that is formed when chromosomes that have undergone a reciprocal translocation attempt to synapse during meiosis; this structure contains two normal chromosomes and two translocated chromosome; eight total chromatids are found within the cross
semisterility
condition in which an individual has lowered fertility
euploid
describes an organism in which the chromosome number is an exact multiple of a chromosome set
triploid
describes an organism or cell with three sets of chromosomes
tetraploid
describes an organism with four sets of chromosomes (4n)
polyploid
describes an organism or cell with three or more sets of chromosomes
aneuploid
not euploid; refers to a variation in chromosome number so that the total number of chromosomes is not an exact multiple of a set (or of the number n)
trisomic
describes a diploid cell or organism with one extra chromosome (ie 2n + 1)
monosomic
describe a diploid cell or organism that is missing a chromosome (ie 2n – 1)
nondisjunction
event in which chromosomes do not segregate properly during mitosis or meiosis
haplodiploid
describes a species, like certain bees, in which one sec is haploid (ie male) and the other sex is diploid (ie females)
endopolyploidy
in a diploid individual, the phenomenon in which certain cells of the body are polyploid
polytene chromosome
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
chromocenter
the central point where the chromosomes of a polytene chromosome aggregate
meiotic nondisjunction
the event in which chromosomes do not segregate properly during meiosis
mitotic nondisjunction
an event in which chromosomes do not separate properly during mitosis
alloploid
describes an organism that contains sets of chromosomes from two or more different species
complete nondisjunction
event in which all the chromosomes fail to segregate properly during meiosis or mitosis and remain in one of the two daughter cells
mosaicism
condition in which the cells of part of an organism differ genetically from those of the rest of the organism
autopolyploid
a polyploid produced within a single species due to nondisjunction
allodiploid
describes an organism that contains one set of chromosomes from two different species
allopolyploid
describes an organism that contains two (or more) sets of chromosomes from two (or more) species
allotetraploid
describes an organism that contains two sets of chromosomes from two different species
