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cytogentics
| Question | Answer |
|---|---|
| karyotype analysis | Used to visualise human chromosomes. Banding pattern on chromosomes is specific to each chromosome |
| karyotype method | 1. mitogen added to cells eg: phytohaemoglutinin 2. culture cells for 48-72 hrs 3. arrest cells in metaphase using colcemid 4. cells fixed onto slide and strained with giemsa dye to show bands on chromosomes |
| paris nomemclature | -chromosomes numbered according to size |
| metacentric | centrosome is in the middle |
| acrocentric | centrosome is near the end so one arm of each chromosome is much shorter |
| subcentric | centrosome is off centre |
| p | short arm of chromatid |
| q | long arm of chromatid |
| FISH | flourescent in situ hybridisation |
| FISH method | -Flourescently labelled DNA probes are created to be complementary to target DNA. -The probe and target DNA hybridise. -specimen washed to remove unbound probes -Flourescent microscope used to visualise areas the probe bound to to see gentic changes |
| chromosome translocations | when a piece of one chromosome breaks off and attches to another part. can be balanced (no genetic info lost/gained) so not pathogenic. can cause issues in meiosis and associated with leukaemias. identified with karyotyping. |
| chromothripsis | Shattering of a chromosme causing it to become all scrambled up. frequently occurs in cancers. |
| satellites | short arms of chromosomes 13,14,15,21 and 22. contains repetitive sequences and ribsomal DNA. |
| Advantages of karyotype analysis | -large changes are easily observable -good if you dont know exactly what youre looking for -quick and easy |
| disadvantages of karyotype analysis | changes smaller than 5Mb missed |
| advantages of array CGH | -can identify gain/loss of chromosomal regions smaller than 5Mb (that karyotyping can't detect) -can't detect balanced translocations |
| array CGH | array comparative genomic hybridisation |
| SNP array hybridisation | |
| Short tandem repeat assay | -STR regions amplified with PCR -region size is measured to determine the number of repeats - number of repeats is compared. |
| How does meiosis create genetic diversity in gametes? | -during meiosis I prophase, crossing over at chiasmata. -chromosmes are randomly assorted into gametes -random fertilisation |
| Crossing over/recombination | The closer DNA variants are on the chromosome, the less likely a cross over will happen between them |
| linkage analysis | DNA markers can be used to track the inheritance of polymorphisms |
| The process of meiosis in females | -Begins in fetal development -meiosis arrests (dictyate) after prophase I (recombination happens) -resumes at ovulation and stops at meiosis II -completes after fertilisation |
| Aneuploidy | when an organism/cell has has a few chromosomes missing or added |
| down syndrome | trisomy 21- 3 copies of chromosome 21. not too severe. |
| patau syndrome | trisomy 13- very severe, most babies die before 6 months |
| edwards syndrome | trisomy 18- very severe, 50% of babies die within the first month. |
| Risk factors for trisomies | increased materal age is a big risk factor- age 20= 1 in 1500 chance, age 45= 1 in 30 chance |
| X inactivation | When one of the X chromosoes in females is silenced so only one set of x linked genes are expressed. |
| Turner syndrome | 45, X. (one x chromosome) |
| Turner syndrome symptoms | Short stature, organ abnormalities, infertility, normal intelligence. |
| Klinefelter Syndrome | 47, XXY, males |
| Klinefelter syndrome symptoms | interfertile, tall, female body fat distribution |
| Trisomy X | 47, XXX, mostly undiagnosed as no distinct phenotype |
| Jacob's syndrome | 47, XYY, occurs in males |
| Jacob's syndrome symptoms | tall, behaviour problems (not many distinct symptoms) |
| Trisomy 21 cause | non-disjunction in first meiotic division (70% of cases) |
| Trisomy 21 phenotype | -cognitive impairment -characteristic facial features eg: epicanthic folds -heart defects -Alzheimers disease (100% chance at age 70) due to extra copy of the amyloid precursor protein gene) |
| Trisomy 21 diagnosis | Karyotyping |
| Haploinsufficiency | when a person only has one functional copy of a gene but it not enough to maintain normal function, leading to diseased phenotype |
| microdeletions | deletions in genes that are 1 to 5 Mb. not visible on karyotype. |
| what causes microdeletions? | unequal cross over/recombination events in meiosis |
| What deletion causes VCFS? | microdeletion on long arm of chromosome 22. 22q11 |
| VCFS symptoms | intellectual/developmental disabilities, SVAS, elfin face |
| How is VCFS diagnosed? | FISH witha DNA probe for the c22q11 region. deletion too small to be seen with banding techniques. |
| Williams-Beuren syndrome (WBS) cause | 1.4Mb deletion on chromosome 7q. usually 25-27 genes deleted. Haploinsuffficiency of these genes causes the characteristics. |
| WBS symptoms | -suprvalvular aortic stenosis (SVAS, narrowing of aorta) -mild learning disability + behaviour abnormality -elfin face hypercalcaemia (high calcuim) |
| cytogentics | the use of techniques (eg: banding and manipulation) to study tissues/cells to look for changes and abnormalities in the chromosomes. |
| Supravalvular aortic stenosis (SVAS) cause | balanced translocation that disrupts the elastin gene on c7q11. Haploinsufficiency of elastin gene. |
Created by:
peasandrice