Chapter 8_Variation In Chromosome Structure And Number Flashcards
The three most commonly used features of classifying chromosomes are
Location of centromere, size, and banding patterns.
The 4 different positions of the centromere
- Metacentric: The centromere is near the middle
- Submetacentric: Slightly off center
- Acrocentric: Significantly off center
- Telocentric: Is at one end
Is the chromosome ever exactly in the center?
No, so it has a short arm “p” and a long arm “q”
Simple vs. Reciprocal Translocation
- Simple: A single piece of chromosome is attached to another chromosome
- Reciprocal: Two different types of chromosomes exchange pieces, thereby producing two abnormal chromosomes carrying translocations.
Terminal Deletion
A normal chromosome has broken into two separate pieces. The piece without the centromere is lost and degraded.
Interstitial Deletion
A chromosome has broken in two places to produce three chromosomal fragments. The central fragment is lost, and the two outer pieces reattach to each other.
Copy Number Variation (CNV)
A type of structural variation in which a segment of DNA, which is 1000 bp or more in length, exhibits copy number differences among members of the same species.
What are the possibilities of CNV?
- Some members of a species may carry a chromosome that is missing a particular gene or part of a gene.
- May involve duplication.
Segmental Duplication
The homolog with two copies of gene A
Pericentric vs. Paracentric Inversion
- Pericentric: The centromere lies within the inverted region of the chromosome
- Paracentric: The centromere is found outside the inverted region.
Position Effect
A chang ein phenotype that occurs when the position of a gene changes from one chromosomal site to a different location.
Inversion Heterozygote
An individual carrying one copy of a normal chromosome and one copy of an inverted chromosome.
Inversion Loop
For the normal chromosome and inversion chromosome to synapse properly, an inversion loop must form to permit the homologous genes on both chromosomes to align next to each other despite the inverted sequence.
Dicentric Chromosome
Contains two centromeres
Dicentric Bridge
The region of the chromosome connecting the two centromeres
Acentric Fragment
Crossover that produces a piece of chromosome without any centromere. It is lost and degraded in subsequent cell divisions.
Telomeres
Specialized repeated sequences of DNA found at the end of normal chromosomes. Telomeres allow cells to identify where a chromosome ends and prevent the attachment of chromosomal DNA to the natural ends of a chromosome.
Euploid
Have a chromosome number that is an exact multiple of a chromosome set.
Triploid
Contains three sets of chromosomes (3n)
Polypoid
Three or more sets of chromosomes
Aneuploidy
Alteration in the number of particular chromosomes.
Trisomic
(2n + 1)
Nondisjunction
The chromosomes do not segregate properly
Endopolyploidy
The occurrence of polyploid tissue or cells in organisms that are otherwise diploid
Polytene Chromosome
Repeated rounds of chromosomal replication produce a bundle of chromosomes that lie together in a parallel fashion.
Meiotic Nondisjunction
Produce haploid cells that have too many or too few chromosomes. If such a cell gives rise to a gamete that fuses with a normal gamete during fertilization, the resulting offspring will have an abnormal chromosome number in all of its cells.
Mitotic Nondisjunction
Abnormal disjunction after fertilization in one of the somatic cells. Leads to a patch of tissue.
Alloploid
Contains sets of chromosomes from two or more different species.
When does nondisjunction occur?
During anaphase of meiosis I or meiosis II (or during anaphase of mitosis)
Complete Nondisjunction
A diploid cell and a cell without any chromosomes.
Bilateral Gyandromorph
One half of the organism becomes female and one half becomes male
Autopolyploid
An individual with one or more extra sets of chromosomes.
Alloploidy
A result of interspecies crosses
Homeologous
Evolutionarily related chromosomes from two different species.
