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our regular amount of chromsomes
we usually has 46 chromosome ( 23 pairs)
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Ploidy
When you do not have a normal number of chromosome
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what are the 4 chromosomal abnormailiteis
- ploidy
- translocations/rearrangements
- delletions/duplications
- Genomic imprinting
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Triploidy
- 69 chromosome instead of 46
- we have a complete extra set of chromosome
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Chances and complication of triploidy
- 1/10000
- fetuses never full develop or die shortly after birth
- dispermy
- spontaneous abortion
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Tetraploidy
- 2 extra sets of chromsomes
- rare conceptions
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Monosomy
a single chromsome is missing
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Trisomy
having an extra chromosome
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what arse the trisomies that are viable
Trisomy 13,18, and 21
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What Monosomy(ies) are/is viable
monosomy x
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What is Nondisjunction?
This is the reason a trisomy happens
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Where can Nonjunction happen ?
in Meiosis and Mitosis
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What does viable mean in regard to human genetic?
pregnancy will carry through to birth
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What happens when nondisjunction happens in Meiosis I?
- all of the resulting gametes will be defective
- 50% would be trisomy and the remain monosomy.
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what happens when nondisjunction happens in Meiosis II?
only 50% of the gametes are defective. 25% trisomy and the other 25% monosomy
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What are the clinical features of Trisomy 18?
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What is Trisomy 13 called ?
Patau syndrome
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What is Trisomy 18 called ?
Edwards syndrome
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What is Trisomy 21 called ?
Down syndrome
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What are the clinical features of Trisomy 21?
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What are the clinical features of Trisomy 13?
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what is a risk factor of trisomy
Age
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what kind of chromsome can aneuploidy affect?
both sex chromsome and autosome
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who does aneuploidy of the sex chromosomes affect?
male and female
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what is aneuploidy of the sex chromosomes ?
- these conditions are less sever
- and it usually means there is just less information on the x or y chromosomes
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What are the types of sex chromosome aneuploidies
- Klinefelter:XXY
- Turner syndrome: XO
- Trisomy X
- XYY
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what is interesting about the femal XX chromosome?
Women only need one to be active. Therefore the other is inactivated and lay dormant
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Barr body
dense, heterochromatin inactivated X chromosome
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why are barr bodies important ?
- You can determine the geneotype of a female cell by counting the number of bar bodies
- if there is a single bar body this is a normal complement of chr0msome and the pt has 46 xx
- if there are 2 it is 47xxx and so forth
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what are the forms of translocation?
reciprocal and robertsonian
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Reciprocal Translocation and clinical relevance ?
- when two chromosome swap information
- this can lead to chronic myeloid leukemia or Lymphoblastic leukemia if translation happens between chromosomes 9 and 12
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Robertsonian translocation
exchange of genetic material where you have long arms of chromosome( q arms) fuse together and you lose the short arms ( p arms)
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what is the mechanism behind robertsonian transloations that makes it defetive
during meiosis these fused long arm robertsonian chromsomes have a possibility of segregating in an unbalance manner leading to either spontaneous abortion or disease induction
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In what chromosome do robertsonian translocation happen?
- Chromosome 13,14,15,21, and 22
- "acrocentric chromosomes"
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what disease are caused by large chromosomal deletions
- Cri-du-chat
- 46, XY
- this result from deltion of the p arm on chromosome 5
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what disease are caused by chromosomal duplications?
- Charot-MArie-Tooth
- duplication chromosome 17
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Genomic imprinting
- the mode behind differential regulation of which genes are expressed
- epigentic mode of regulation where you have DNA metylation at the CPG on regulator regions of different genes.
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Uniparental disomy
- results from non dis-junction
- having two identical copies of one parents chromosomes.
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Central dogma of genetics
- equal allelic expression regardless if parental origin
- you have a single gene that code for a single mrna that can be translated to a single protein
- 2 allell one from each parent and they are expressed equally
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Prader Willi Syndrome
- deletion on chromosome 15 that is inherited from the father
- P for padre
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Angelman syndrome
deletion on chromosome 15 that is inherited from the mother
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why are prader-willis and angelman syndrom different if the deletion happens on the same chromosome?
- differential genomic imprinting center IC that regulations regulate the genes that code for each of these disease depending on where they are from
- In the paternal the angelman genes are methylated while int he maternal the prader-willis genes are methylated
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Beckwith-Wiedmann Syndrome
- result from differnetial imprinting.
- Genes that are normally methylated and turned off specifically IGF2 and KCNQ1 and not
- when a DMR region is interupted these genes are left unmethylated and the embryo now has two sets of the same genes being expressed and you get an over growth phenotype such as Beckwith-wiedmannn syndrome
- this is due to the over expression of genes
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physical presentation for the patau syndrome: Trisomy 13
- Hypotonia
- Orofacial clefts
- Polydactyly
- Microcephaly
- Microphthalmia
- Cns defects
- 90% have cardiac defects
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Characteristics of Trisomy 18
- edwards syndrome
- distinctive facial features
- overlapping finger and rocket-bottom feet
- 90% have congenital heart defects (VSD)
- severe cognitive impairment and developmental delay
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statistics of Trisomy 21
- dysmorphic features
- hypotonia ( decreased muscle tone)
- 30-40% structural heart defects
- 15-20X increased risk for leukemia
- respiratory infections are more common
- variable intellectual disability (moderate to mild)
- 90% happen from nondisjunction of maternal chromosomes
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Physical features of Down Syndrome
- Microbrachycephaly woth flat occiput
- flat nasal bridge w/ hypoplastic alae Nasi
- Upslanting Palpebae and Epicanthal fold
- Brachydactyly, wide toe gap btw 1st and 2nd
- Single palmar Creas and Clinodactyly
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what sex is more susceptible to incidence of aneuploidy?
males
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Klinefelter syndrome
- 1/500-1000
- taller, hypotonia
- intelligence normal range
- 30% gynecomastia
- Sterile, hypogonadism
- increased risk for osteoporosis and breast cancer
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Turner syndrome
- Infertile, ovarian dysgenesis, lack secondary sex characteristics
- Congenital heart defects
- Normal intelligence-spatial perception diminished
- Short stature, webbed neck
- 60-80% absence of parental X
- 1/5,000 - 10,000 births
- 50% ( 45X)
- 30-40% mosaic ( 45,X,46XX)
- 10-20% deletion of Xp
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what are the characteristics of Turner's syndrome?
- shot stature, webbed neck
- lack of secondary sex characteristics
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name of all the sex chromosome aneuploidies
- trisomy X
- XYY
- Klienfelter
- Turners
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Cri-du-chat
- 26,Dy del ( 5p)
- They have low Id and microcephaly
- a chromosomal deletion
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what is the difference between angelman and Prader-willis syndrome in physical characteristics
angel man siezures, ataxic gate, sever developmental delay, sever spech impairment, microcephaly,
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Beckwith-Weidmann syndrome
- overgrowth
- growth asymmetry
- Organomegaly- accessory organs
- increased tomaur incidence
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what causes Backwith-Wieldman syndrome?
- improper methylation
- uniparential paternal disomy
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Know different conditions of ploidy (polyploidy, aneuploidy) and how they occur
2. What are the chromosome abnormalities discussed
3. Know common syndromes associated with chromosome abnormalities
4. Robertsonian translocations
5. Genomic imprinting and disomy
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