20 Questions
What is the term for any chromosome number that is not an exact multiple of the number in a haploid gamete?
Aneuploidy
What is the term for a condition where there is an extra set of the entire genome (3n, 4n, etc.)?
Polyploidy
What percentage of live births are cytogenetic disorders present in?
~1%
What type of cells have a normal set of chromosomes (n= chromosome number)?
Haploid cells
Which type of chromosome rearrangement involves a segment removed from one chromosome being inserted into a different chromosome?
Insertion
What is the risk of producing a child with Down Syndrome for a maternal carrier of a Robertsonian translocation?
8%
Which type of chromosome rearrangement involves a chromosome with two centromeres?
Dicentric chromosome
What is the characteristic feature of an isochromosome?
One arm duplicated in a mirror-image fashion
What is the mechanism of formation of an isochromosome?
Misdivision through the centromere in meiosis II
What is the characteristic feature of a ring chromosome?
Two breaks and broken ends reunite in a ring
What type of rearrangement involves unidentified chromosomes called 'marker' chromosomes?
Ring chromosome
What are the mechanisms involved in the formation of duplication?
Unequal meiotic crossing-over
What type of rearrangement involves loss of a tiny piece that cannot be seen in routine cytogenetic examination?
Deletion
What is the risk of producing a child with Down Syndrome for a paternal carrier of a Robertsonian translocation?
2-3%
What is the term for two or more genetically different cell lineages within one individual?
Mixploidy
Which condition results from a failure of chromosomes to separate during meiosis or mitosis?
Aneuploidy
What is the term for three sets of chromosomes (3n), most commonly from dispermic fertilization or failure of a meiotic division?
Triploidy
Which type of rearrangement involves a fusion of two acrocentric chromosomes, leading to a loss of short arms and a balanced karyotype with 45 chromosomes?
Robertsonian translocation
What term describes chromosome number not a multiple of basic chromosome set, the most common and clinically significant type of human chromosome disorders?
Aneuploidy
What condition results from one extra chromosome, such as Down Syndrome (Trisomy 21, 47,XX,+21)?
Trisomy
Study Notes
- Mixploidy: Two or more genetically different cell lineages within one individual, either through mosaicism (one zygote) or chimerism (different zygotes)
- Triploidy: Three sets of chromosomes (3n) - Most commonly from dispermic fertilization or failure of a meiotic division
- Euploidy tetraploidy: Four sets of chromosomes (4n) - Rare in live births, common in tumors, can be caused by failure of cell division
- Nondisjunction: Failure of chromosomes to separate during meiosis or mitosis, leading to aneuploidy
- Aneuploidy: Chromosome number not a multiple of basic chromosome set, most common and clinically significant type of human chromosome disorders
- Monosomy: One chromosome missing, such as Turner Syndrome (45,X)
- Trisomy: One extra chromosome, such as Down Syndrome (Trisomy 21, 47,XX,+21), Edwards Syndrome (Trisomy 18, 47,XY,+18), and Patau Syndrome (Trisomy 13, 47,XX,+13)
- Structural rearrangements: Result from chromosome breakage and reconstitution, balanced and unbalanced
- Balanced rearrangements: No loss or gain of genetic information, carry a risk of unbalanced offspring, include inversions, translocations, and insertions
- Unbalanced rearrangements: Net gain or loss of DNA, larger deletions or duplications have greater phenotypic consequences.
- Robertsonian translocation: A type of unbalanced rearrangement involving the fusion of two acrocentric chromosomes, leading to a loss of short arms and a balanced karyotype with 45 chromosomes.
Test your knowledge about chromosome abnormalities and their role in genetic diseases. Learn about the identification of specific syndromes and their association with malignancy and congenital malformations.
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