Aneuploidy (Lec 12) Flashcards
Define Aneuploidy
a change in the number of individual chromosomes
A type of aneuploidy where there is a loss of both members of a pair of homologous chromosomes is called what?
nullisomy
A type of aneuploidy where there is a loss of a single chromosome (2n-1) is called what?
monosomy
A type of aneuploidy where there is a gain of a single chromosome (2n+1) is called what?
trisomy
A type of aneuploidy where there is a gain of two homologous chromosomes (2n+2) is called what?
tetrasomy
What is double trisomy?
gain of two non homologous chromosomes (2n+1+1)
What is double monosomy?
loss of two non homologous chromosomes (2n-1-1)
What is double tetrasomy?
gain of two extra pairs of homologous chromosomes (2n+2+2)
If nondisjunction occurs in meiosis I, what are the resulting zygotes?
trisomic (2n+1) or monosomic (2n-1)
If nondisjunction occurs in meiosis II, what are the resulting zygotes?
trisomic (2n+1), monosomic (2n-1), or normal diploid (2n)
Aneuploidy affects number of gene copies but not nucleotide sequences, therefore, effects of aneuploidy are most likely due to what?
abnormal gene dosage
True or false?
X-inactivation in mammalian females is an example of dosage compensation
true
In regards to aneuploidy in humans, what type of chromosomes are most commonly involved?
sex chromosomes
Primary Down Syndrome (trisomy 21) usually arises from nondisjunction in which part of meiosis I?
oogenesis of meiosis I
About 4% of those with Down syndrome have 46 chromosomes with extra part of chromosome via translocation. This type of Down syndrome that arises from carriers of chromosomes that have undergone a Robertsonian translocation is called what?
Familial Down syndrome
Between what two chromosomes does the Robertsonian translocation occur in Familial Down syndrome?
14 and 21
In regards to Familial Down syndrome, how many chromosomes do the translocation carriers have and do they have down syndrome?
45; no they do not have Down syndrome
In regards to Familial Down syndrome, what are the three possible ways for segregation to occur in a translocation carrier?
Translocation chromosome may separate from normal 14 and 21 chromosomes
gametes = half with translocation chromosomes and half with normal 14 and 21 chromosomes
gametes = half with normal 21+ translocation chromosome and half with 14 but no 21 chromosome
gametes = half with normal 14+ translocation chromosome and half with 21 but no 14
If a normal person mates with a translocation carrier, what percentage of offspring will be healthy and what percentage will have down syndrome?
2/3 healthy, including the translocation carriers
1/3 will have Down syndrome
note: other chromosomal combinations result in aborted embryos
What are some characteristics of Trisomy 10: Edward syndrome?
1 in 8,000 births severely retarded low-set ears short neck deformed feet clenched fingers heart problems die within a year typically
What are some characteristics of Trisomy 13: Patau syndrome?
1 in 15,000 births severe mental retardation small head sloping forehead small eyes cleft lip and palate extra fingers and toes half die within a month of birth, rest by age of 3
What are some characteristics of Trisomy 8?
mental retardation contracted fingers and toes low-set malformed ears prominent forehead often a normal life expectancy
The following condition occurs when both chromosomes of a homologous pair are inherited from the same parent - most cases probably arise as a trisomy with one of the three homologs chromosomes lost early in development
uniparental disomy
note: trisomics typically do not survive
ex: cystic fibrosis and prader-willi
What is Mosaicism?
occurs when there is nondisjunction in mitosis and is often found in Turner’s syndrome (45, XX/46, XX)
