10/20 Genetics

Question 1

What are the effects of trisomy 18

Answer 1

edwards syndrome

Question 2

what are the three anisomy trisomy that is compatible with live birth?

Answer 2

Thri 18; Tri 13; Tri 21

Question 3

what are the symptoms of trisomy 16?

Answer 3

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

Question 4

what is the effect of trisomy 13?

Answer 4

Patau syndrome

Question 5

how many of the tri 13/18 are lost before birth?

Answer 5

90%

Question 6

what are the feature of the pataue syndrom?

Answer 6

postaxial polydactyly; often omphalocele; and some midline defects (cleft lip or palate.

Question 7

what is one eye called or other mid-line defects

Answer 7

holoprosencephaly –can be

Question 8

what is the gene that causes holoprosencephaly?

Answer 8

sonic hedge hog

Question 9

what is the take-away for tri 13/18 survival

Answer 9

although usually lethal, some tri 13/18 can survive and reach some developmental milestones

Question 10

how does occurance of trisomy 13/18 change with age of mother

Answer 10

they go up! esp. after 35

Question 11

where is most of the tri 13/18 come from –maternal or paternal?

Answer 11

from the maternal

Question 12

what is the result of having only one X as a sex chromosome

Answer 12

Turner syndrome

Question 13

why does turner syndrome happen when you usually inactivate the x chromosome anyway?

Answer 13

there is about 15-20% of the ggenes on the inactive x chromo that are not inactive

Question 14

what are the phenotype of terner syndrom?

Answer 14

reduced stature; webbed neck; shield shaped chest; gonadal dysgenesis; sterility; renal malformations; aortic coarctation; diminished spatial IQ

Question 15

why reduced stature in turner syndrome

Answer 15

shox transcrition factor gene deleted

Question 16

what is cystic hygroma?

Answer 16

a large cyst associated with turner syndrome

Question 17

where is the SHOX gene?

Answer 17

on the distal 2.6 Mb of X or the distal tip of the Y and escapes silencing in silencing the X chromosome

Question 18

how many of the turner syndrome conceptions are lost?

Answer 18

99% of them – acounts for 10-15% of first trimester miscarriages.

Question 19

How could a turner syndrome baby survive?

Answer 19

by being a mosaic where some of the cells lose one of the X chromosomes after fertilization.

Question 20

how can treat turner syndrome?

Answer 20

growth hormone treatment; estrogen replacement; gonadectomy; monitor for cardiovascular defects; psychiatric management when needed.

Question 21

what is the result of having XXY?

Answer 21

klinefelter sydrome

Question 22

Klinefelter syndrome phenotypes

Answer 22

increseased stature; hypogonadism; sterility; female habitus; gynecomastia; reduced IQ;

Question 23

what if there is XXX

Answer 23

then you have a rather mild phenotype of increased stature, hypertelorism; premature ovarian failure; slight IQ reduction; and wide set eyes.

Question 24

what if XYY?

Answer 24

then you get a slight phenotype of increased stature and slight IQ reduction.

Question 25

what percent of the numerical chromosome abnormalities are from the mother or father?

Answer 25

1-2% from the paternal; 20-25% are maternal gametes in origin

Question 26

what percent of the structural abnormalities are from paternal/maternal gametes?

Answer 26

5% paternal; 1% maternal

Question 27

what if fusion of long arms of acrocentric chromosomes 13 and 14? (missing 14 and very large 13 chromosome)

Answer 27

Robertsonian translocation.

Question 28

what is a acrocentric chromosme

Answer 28

a chromosome where the centromere is neat the tip of the chomosome and not in the middle: 13, 14, 21 etc.

Question 29

what happens if you have a robertsonian translocation of chromosome 21?

Answer 29

down syndrome!

Question 30

what is the difference in a balanced and not balanced robertsonian translocation

Answer 30

you get a net trisomy or monosomy or normal expression if it is balanced or not.

Question 31

why would it be important to know if the down syndrome is due to translocation or a true trisomey

Answer 31

the recurence is much higher with translocation

Question 32

what is a partial trisomy and monosomy and how can that happen?

Answer 32

reciprocal translocation: exchange between non-homologous chromosomes.

Question 33

what is the philedelphia chromosome and how does it happen

Answer 33

reciprocal translocation between 9 and 22.

Question 34

what does a philadelphia chromosome do?

Answer 34

causes chronic myelogenous leukemia by fusing the ABL proto-oncogene with the BCR promoter gene!

Question 35

what is the treatment for the philadelphia chromosome?

Answer 35

gleevac (imatinib) binds to BCR-ABL ATP binding site and stops it!

Question 36

what if there is a deletion of the short arms of 5?

Answer 36

then you get Cri-du-Chat (cry of the cat): 46,XX,del(5p); you get low IQ and small head etc.

Question 37

what if extra short arm of 5?

Answer 37

then you get a mild form of Cri-du-Chat! deletion is worse than duplication!

Question 38

how could a XX be a male?

Answer 38

by SRY gene placement on the X chromosome during male meiosis.

Question 39

What is FISH?

Answer 39

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.

Question 40

what is comparative genomic hybridization.

Answer 40

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.

Question 41

what is a possible application of FISH

Answer 41

to make sure that you are implanting a good zygote in invetro implantiation.

Question 42

what are the advantages of FISH

Answer 42

done at any cell stage and can highlight abnormalities in higher resolution

Question 43

what is the basic application of CGH analysis of DNA?

Answer 43

to check for chromosomal deletions or duplications.

Question 44

what is a common patient to get checked with CGH?

Answer 44

children with any significant developmental delays.