Sheet 3 Flashcards
(37 cards)
What are telomeres?
Repetitive sequences that exist at the end of all the chromosomes and do not encode for genes.
All 46 chromosomes carry the same telomeric pattern, which is:
TTAGGG
What is the main reason for aging?
Telomerase is switched off = DNA is lost from the telomere
What is Aneuploidy?
Any chromosome number that is not an exact multiple of haploid number
What are 2 examples of aneuploidy?
1) Trisomy: The presence of an extra chromosome.
2) Monosomy: The absence of a single chromosome.
What is the cause of aneuploidy?
Nondisjunction
Aneuploidy results from the
fertilization of which gametes?
The gamete in which the nondisjunction occurred
What is Polyploidy/Euploid?
Is when an organism has more than two complete sets of chromosomes (extra but exact multiples of n).
What are 2 examples of Polyploidy/Euploid?
1) Triploidy (3n) is three sets of chromosomes (3 copies per chromosome).
2) Tetraploidy (4n) is four sets of chromosomes.
Polyploidy is common in:
Plants (not animals)
Who is more normal in appearance: Polyploids or aneuploids?
Polyploids
What can cause Polyploidy/Euploid?
When two sperms fertilize an egg by mistake (lethal to the fetus).
What is a common karyotype for Polyploidy/Euploid?
XXY
Breakage of chromosomes can change their structures in four different ways:
1) Deletion: Removes a chromosomal segment
2) Duplication: Repeats a segment
3) Inversion: Reverses the orientation of a segment within a chromosome
4) Translocation: Moves a segment from one chromosome to another
What is the difference between recombination and translocation?
Recombination is the exchange of DNA between non-sister chromatids of homologous chromosomes (happens in meiosis to give diversity).
Translocation is the exchange of genetic material between non-homologous chromosomes.
What is Trisomy 21 (Down syndrome)?
An aneuploid condition that results from having three copies of chromosome 21.
How many children born in the United Sates have Down Syndrome?
1 out of every 700
What correlation is related to Down Syndrome? Is there a cause for the correlation?
Maternal age and the risk of down syndrome; We don’t know why they’re
related.
What should a mother who is pregnant at an advanced age do?
Karyotyping for the amniotic fluid or chorionic villi to check for trisomy 21 in the fetus.
What is the male to female ratio for Trisomy 21?
3:2
What is Down Syndrome clinically characterized by?
1) Mental retardation (IQ 25-50)
2) Low nasal bridge (90%)
3) Hypotonia (80%): Loose muscles
4) Up slanting palpebral fissures (80%)
5) Small, low-set ears (60%): A classical clinical abnormality for chromosomal aneuploidy
6) Congenital heart disease (30%-50%)
7) Epicanthic folds in the eye
8) Protruding tongue
9) Intestinal problems
10) Gap between first and second toes
11) 15-fold increase in risk for leukemia
12) Simian line (transverse crease) (45%): One line in their hand
13) Distinct facial features
Which clinical Features are easily recognized at birth?
1) Low nasal bridge (90%)
2) Hypotonia (80%): Loose muscles
3) Up slanting palpebral fissures (80%)
4) Congenital heart disease (30%-50%)
5) Epicanthic folds in the eye
6) Simian line (transverse crease) (45%): One line in their hand
Approximately how many children with Down Syndrome and congenital heart disease die during their first year?
40%
What are the congenital heart problems seen in Trisomy 21?
1) VSD (Ventricular Septal Defect)
2) AV canal defects
