9 28 Genetics-Table 1

Question 1

what is genetic imprinting?

Answer 1

in imprinting the gene is inactivated (not transcribed) when transmitted by one of the two sexes: Aa is not equal to aA. therefore it matters if the gene is from the mother or from the father.

Question 2

how does imprinting happen?

Answer 2

associated with methylation and chromatin condensaiton.

Question 3

methylation and chromatin condenstiaon are both examples of?

Answer 3

epigenetic effects

Question 4

symptoms of Prader-Willi Syndrome

Answer 4

Mild/mod. intellectual disability. Small hands/Feet; Hypogonadism; Obesity/hyperphagia; hypotonia;

Question 5

what is parthenogenesis and why doesn’t it work?

Answer 5

an unfertilized egg (or egg w/ only paternal genes) gives rise to an offspring. this doesn’t work because of imprinting!

Question 6

why does a parthenogenesis lead to a hyditiform mole?

Answer 6

if you get all the genes from dad, then because of imprinting you get many genes that simply aren’t active because of imprinting

Question 7

what is the major cause of Prader-willi syndrome?

Answer 7

due to 4Mb deletion of chromosome 15q

Question 8

summerized the idea of imprinting:

Answer 8

the sperm or overy silents specific sections of the gene during spermogenisist/oogenistis and this is passed to the offspring. therefore only the gene from one parent is active at all.

Question 9

how do we get deletions or duplicates that are highly conserved i.e. the loss of 4Mb of chromosome 15q

Answer 9

unequal crossing over during meiosis

Question 10

symptoms of angleman syndrome

Answer 10

severe intellectual disabilities; ataxia (characteristic gait and posture); seizures; spontaneous, uncontrolled laughter; 10% of cases due to 4Mb deletion of chromosome 15q.

Question 11

how can the same deletion in the 4Mb region of 15q lead to two different diseases?

Answer 11

if get the deletion from the chromsome from dad, then you get prader-willi syndrome; if you get the deletion from mom, then you get angelman syndrome. that is because of imprinting.

Question 12

what is the chromosomal explination for why loss of the same chromosome section can lead to either prader-willi or angelman?

Answer 12

in paternal chromosome you get the active PWS region gene in the maternal you get the active AS gene. the paternal has a silent AS gene and the maternal has a silent PWS region gene. therefore if you lose one or the other chromosome then you get either prader-willi or angelman.

Question 13

what is the genelogical evidence for imprinting in PWS?

Answer 13

Mom who has PWS mated and passed on the deletion to the daughter, who had AS!

Question 14

what is uniparental disomy?

Answer 14

one parent, two chromosomes: two copies of a chromosome inherited from one parent.

Question 15

how can uniparental disomy happen?

Answer 15

this can happen from two chromosomes from dad and none from mom. or, two from one parent and one from another, and then lose one of the three and have only two maternal or two male chromosomes

Question 16

if you had a uniparental disomy with two maternal chromosome 15s you get AS or PWS?

Answer 16

get AS!

Question 17

symptoms of Bechwith-wiedemann

Answer 17

large size for gestational age; large tongue; increased incidence of wilms tumor, hepatoblastoma

Question 18

what is the chomosomal explination for the large gestational size of Bechwith-wiedemann

Answer 18

usually IGF2 growth factor is imprinted in maternal chromosome to be inactive. If this imprinting is lost in the maternal chromosome then the maternal IGF2 is active and then over-express IGF2 and very large babies: Bechwith-wiedemann

Question 19

Russel-silver syndrom

Answer 19

deficient IGF2 expression therefore short stature due to growth slowing

Question 20

what is the general trend in imprinting of growth factors?

Answer 20

fathers tend to express genes that enhance fetal growth, and mothers tend to express genes that suppress fetal growth

Question 21

what could be a cuase of Russel-silver syndrome?

Answer 21

the gain of imprinting in paternal gene for expression of IGF2?

Question 22

Myotonic dystrophy

Answer 22

myotonia (can’t let go); loss of muscle tone; cardiac arrhythmia; testicular atrophy; cataracts; frontal baldness in males.

Question 23

what is the inheritance type of myotonic dystrophy?

Answer 23

autosomal dominant condition

Question 24

what is anticipation in an inherited condition?

Answer 24

the condition is seen earlier and earlier in each generation of the disease due to a lengthening of the tri-base repeat section

Question 25

what cuases myotnic dystrophy

Answer 25

caused by expansion of a CTG repeat in the 3’ region of the DMPK. (this is an untranslated section of the gene)

Question 26

how can a non-coding section of DNA cause Myotonic Dystrophy

Answer 26

abnormal mRNA interferes with RNA-binding protiens affecting splicing of other genes or a “toxic RNA” that compromises the RNA splicing of many genes.

Question 27

what causes the “anticipation” in myotnic dystrophy

Answer 27

increasing size of the repeat in subsequent generations gives earlier onset

Question 28

Symptoms of Fragile x syndrome

Answer 28

intellectual disability; behavioral disorders; large ears, jawas, macro-orchidism; joint hyperextensibility

Question 29

what is the chromosme abnormality that cuases fragile x

Answer 29

the tips of the x chromosome has a very condensed region of DNA

Question 30

why is the inheritance of fragile x through the generations see a higher rate of penetrance?

Answer 30

anticipation; or the increasing size of a non-coding tri-nucleotide expansion.