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37 terms

Chapter 8

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Chromosome Mutations or Chromosome Aberrations
Changes in the total number of chromosome, such as a deletion or rearrangement
Aneuploidy
Variations in chromosome number. When an organism gains or loses one ore more chromosomes and has other than an exact multiple of the haploid set
Euploidy
Completely haploid sets of chromosomes are present
Polyploidy
Occurs when more than two sets of chromosomes are present
Nondisjunction
Chromosomal variation arises from nondisjunction, where chromosomes or chromatids fail to disjoin and move to opposite poles during Meiosis I or II
Monosomy
The loss of one chromosome to produce a 2n-1 complement
Trisomy
2n+1 Chromosomes. Often lethal for autosomes, but not sex chromosomes. Three copies of one chromosome are present so pairings are irregular.
Trivalent
When three copies of a chromosome are synapsed
Univalent
An unpaired chromosome, can be present along with a bivalent instead of a trivalent. When 3 chromosomes aren't synapsed, instead 2 are and 1 is left unpaired.
Down Syndrome
Results from trisomy of chromosome 21
Familial Down Syndrome
Runs in families, involve a translocation of chromosome 21
Amniocentesis or Chorionic Villus Sampling (CVS)
Testings for women who become pregnant late in their reproductive years
Patau Syndrome
Trisomy 13
Edwards Syndrome
Trisomy 18
Triploid
3n
Tetraploid
4n
Pentaploid
5n
Autopolyploidy
The addition of one or more sets of chromosomes identical to the haploid complement of the same species
Allopolyploidy
The combination of chromosome sets from different species as a consequence of interspecific matings
Allotetraploid
Arises from hybridization of two closely related species
Endopolyploidy
The condition in which only certain cells in an otherwise diploid organism are polyploid
Deletion (deficiency)
Chromosome breaks in one or more places and a portion if it is lost, the missing piece.
Terminal Deletion
Deletion near one end
Intercalary Deletion
Deletion from the interior of the chromosome
Cri-du-chat
Results form a segmental deletion of a small terminal portion of the short arm of chromosome 5
Duplications
Arise as the result of unequal crossing over during meiosis or through a replication error prior to meiosis
Gene Redundancy
ORganisms that have multiple copies of ribosomal RNA genes (rRNA)
Gene Amplification
A mechanism to increase the rRNA
Inversion
Involves a rearrangement of the linear gene sequence rather than the loss of genetic information. Segment turned 180 degrees in a chromosome, requires two breaks and reinsertion of the inverted segment. May arise from chromosomal looping
Paracentric inversion
Does not change the relative lengths of the two arms of a chromosome
Pericentric Inversion
Includes centromere, does change the relative lengths of the two arms of a chromosome
Paracentric inversion crossover
One recombinant chromatid is dicentric (two centromeres) and one is acentric (lacking a centromere)
Translocation
Movement of a chromosomal segment to a new location in the genome
Reciprocal Translocation
Involves the exchange of segments between two nonhomologous chromosomes. Unusual synapsis
Alternate Segregation
Leads to normal and a balanced gamete
Adjacent Segregation
Leads to gametes containing duplications and deficiencies
Fragile Sites
more susceptible to chromosome breakage when cells are cultured in the absence of certain chemicals such as folic acid