10/20 Genetics Flashcards
What are the effects of trisomy 18
edwards syndrome
what are the three anisomy trisomy that is compatible with live birth?
Thri 18; Tri 13; Tri 21
what are the symptoms of trisomy 16?
sever cns defects; congenital heart disease; low,rotated ears, small mouth prominent occiput; houshoe kidneys; rocker-bottom feet; hypertonia; cardiac and renal failure, common causes of death
what is the effect of trisomy 13?
Patau syndrome
how many of the tri 13/18 are lost before birth?
90%
what are the feature of the pataue syndrom?
postaxial polydactyly; often omphalocele; and some midline defects (cleft lip or palate.
what is one eye called or other mid-line defects
holoprosencephaly –can be
what is the gene that causes holoprosencephaly?
sonic hedge hog
what is the take-away for tri 13/18 survival
although usually lethal, some tri 13/18 can survive and reach some developmental milestones
how does occurance of trisomy 13/18 change with age of mother
they go up! esp. after 35
where is most of the tri 13/18 come from –maternal or paternal?
from the maternal
what is the result of having only one X as a sex chromosome
Turner syndrome
why does turner syndrome happen when you usually inactivate the x chromosome anyway?
there is about 15-20% of the ggenes on the inactive x chromo that are not inactive
what are the phenotype of terner syndrom?
reduced stature; webbed neck; shield shaped chest; gonadal dysgenesis; sterility; renal malformations; aortic coarctation; diminished spatial IQ
why reduced stature in turner syndrome
shox transcrition factor gene deleted
what is cystic hygroma?
a large cyst associated with turner syndrome
where is the SHOX gene?
on the distal 2.6 Mb of X or the distal tip of the Y and escapes silencing in silencing the X chromosome
how many of the turner syndrome conceptions are lost?
99% of them – acounts for 10-15% of first trimester miscarriages.
How could a turner syndrome baby survive?
by being a mosaic where some of the cells lose one of the X chromosomes after fertilization.
how can treat turner syndrome?
growth hormone treatment; estrogen replacement; gonadectomy; monitor for cardiovascular defects; psychiatric management when needed.
what is the result of having XXY?
klinefelter sydrome
Klinefelter syndrome phenotypes
increseased stature; hypogonadism; sterility; female habitus; gynecomastia; reduced IQ;
what if there is XXX
then you have a rather mild phenotype of increased stature, hypertelorism; premature ovarian failure; slight IQ reduction; and wide set eyes.
what if XYY?
then you get a slight phenotype of increased stature and slight IQ reduction.
what percent of the numerical chromosome abnormalities are from the mother or father?
1-2% from the paternal; 20-25% are maternal gametes in origin
what percent of the structural abnormalities are from paternal/maternal gametes?
5% paternal; 1% maternal
what if fusion of long arms of acrocentric chromosomes 13 and 14? (missing 14 and very large 13 chromosome)
Robertsonian translocation.
what is a acrocentric chromosme
a chromosome where the centromere is neat the tip of the chomosome and not in the middle: 13, 14, 21 etc.
what happens if you have a robertsonian translocation of chromosome 21?
down syndrome!
what is the difference in a balanced and not balanced robertsonian translocation
you get a net trisomy or monosomy or normal expression if it is balanced or not.
why would it be important to know if the down syndrome is due to translocation or a true trisomey
the recurence is much higher with translocation
what is a partial trisomy and monosomy and how can that happen?
reciprocal translocation: exchange between non-homologous chromosomes.
what is the philedelphia chromosome and how does it happen
reciprocal translocation between 9 and 22.
what does a philadelphia chromosome do?
causes chronic myelogenous leukemia by fusing the ABL proto-oncogene with the BCR promoter gene!
what is the treatment for the philadelphia chromosome?
gleevac (imatinib) binds to BCR-ABL ATP binding site and stops it!
what if there is a deletion of the short arms of 5?
then you get Cri-du-Chat (cry of the cat): 46,XX,del(5p); you get low IQ and small head etc.
what if extra short arm of 5?
then you get a mild form of Cri-du-Chat! deletion is worse than duplication!
how could a XX be a male?
by SRY gene placement on the X chromosome during male meiosis.
What is FISH?
fluorescent label of specific gene probes that hybridize to target regions of DNA in a denatured strand of DNA. this highlights the genes and can easily show number or deletion of genes.
what is comparative genomic hybridization.
you take a control DNA that is normal but with a flourescent marker and hybridize with test DNA with a different colored flourescent signal and then compare the result to see if you get any with just a test or just a control signal that would indicate extra or missing genes.
what is a possible application of FISH
to make sure that you are implanting a good zygote in invetro implantiation.
what are the advantages of FISH
done at any cell stage and can highlight abnormalities in higher resolution
what is the basic application of CGH analysis of DNA?
to check for chromosomal deletions or duplications.
what is a common patient to get checked with CGH?
children with any significant developmental delays.
