Chromosomal Abnormalities & Investigations Flashcards
What happens to centromere with age?
It becomes smaller
What are chromosomes like in interphase?
Longest and thinnest
What are chromosomes like in prophase?
Increase in thickness but decrease in length
What are chromosomes like in anaphase?
The smallest
What are chromosomes like in metaphase?
Very thick, quite short and well spread in the cell
At which stage are chromosomes most easily observed?
Metaphase
What are chromosomes composed of?
DNA, RNA and protein
What are the three classes of chromosomes?
Metacentric, Submetacentric and Acrocentric
What can chromosomal abnormalities cause variation in?
Number and structure
What is aneuploidy?
Variation in the number of chromosome within a set.
Hyperploidy
Hypoploidy
Polyploidy
What are structural changes of chromosomes?
Genetic information can be changed (more or less) or rearranged
What are the two types of mutations?
Chromosome mutation and gene mutation
Examples of chromosome mutation?
Deletion
Duplication
Inversion
Translocation
Examples of gene mutation?
Point mutation: silent, missense, nonsense.
Frame shift: deletion, addition
What are the types of transaction?
Reciprocal and Robertsonian
What is reciprocal translation?
Segments from two different chromosomes are exchanged
What is Robertsonian translocation?
Entire chromosome attaches to another
How are genetic abnormalities detected?
Screening tests
Diagnostic tests
Examples of screening tests?
Ultrasound
Maternal Serum Screening
When is ultrasound performed?
10 to 14 weeks
What are some signs that could portray Down syndrome through ultrasound?
Thickening of skin over the back of the fetal neck “nuchal translucency”
When is maternal serum screening done?
14 to 20 weeks
What does MSS screen for?
Down syndrome and spina bifida
What does MSS measure?
HcG (high levels indicate DS)
α-fetoprotein (low levels indicate DS)
unconjugated estriol (low levels indicate DS)
Examples of diagnostic testing?
Amniocentesis
Chorionic Villus Sampling
When is CVS performed?
10 to 13 weeks
When is amniocentesis performed?
16 to 18 weeks
What is karyotyping?
Study that determines the number and structure of chromosomes and also detects common abnormalities
What allows for karyotyping?
Parents:
- Mother > 35 years old
- 3 or more miscarriages
- Stillbirths with suspected chromosomal abnormality
- Infertility
Family history of:
- chromosome rearrangement
intellectual disability
Patients with:
- Characteristics of chromosomal syndromes
- Delayed puberty
- Congenital abnormalities
- Ambiguous genitalia
Where is the sample for karyotyping collected from?
Peripheral blood
Amniotic fluid
Skin fibroblast
Bone marrow cells
What is the process of karyotyping?
- Collect cell from individual
- Induce the cell to divide
- Stop cell division in metaphase using colchicine
- Stain chromosomes to make them visible using Giemsa stain
Which chromosomes are in Group A?
1 to 3, they are the largest and centromere is in the middle
Which group are chromosomes 6 to 12 and X in?
Group C, mid-size, centromeres located either middle or subterminally
Which chromosomes are in Group B?
4 and 5, large and centromere is at subterminal region.
Which group are chromosomes 13 to 15 in?
Group D, mid-size, centromeres located terminally
What is Group E?
Chromosomes 16 to 18, slightly smaller than D. 16 has centromere in middle, 17 and 18 at more distal regions
Which chromosomes are in Group G?
21, 22 and Y, Y is longer than 21 and 22
What is Group F?
19 to 20, short chromosomes, centromere in the middle
What are the different kinds of Down syndrome?
Trisomy 21, Translocation trisomy 21, Mosaic Trisomy 21
What are some clinical features of DS?
Upslanting eyes
Epicanthic folds
Flat nasal bridge
Low-set small ears,
Short neck,
Abnormal teeth
Short broad hands,
Transverse palmar crease
Space between the first and second toea
What are some other issues that come along DS?
Intellectual disability
Dementia
Heart Disease
GI Abnormalities
Obesity
Eye Problems
Hearing Loss
Endocrine Disorders
Haematological Disorders
What is Turner Syndrome?
45 XO
Main features of Turner Syndrome?
Puffy hands and feet
Webbing of neck
Short stature
Low hairline at the back of the neck
Broad chest, widely spaced nipples
Poorly formed or absent ovaries
Infertility
Learning disabilities
What is 47, XXY?
Klinefelter syndrome
Main features of Klinefelter syndrome?
Lower IQ
Tall stature
Poor muscle tone
Reduced secondary sex characteristics
Gynaecomastia
Small testes/infertility
Sparse body hair
What happens if there is triploidy, 69 chromosomes?
Lethal condition
What is Cri-du-Chat?
46, XX, del(5)
Main features of Cri-du-Chat?
High-pitched cry,
Widely set eyes
Low-set ears,
Small jaw,
Downward slanting fissures
Microcephaly,
Intellectual disability
What is Edward’s?
Trisomy 18
What is Patau’s?
Trisomy 13
What is a chromosomal abnormality caused by duplication?
Pallister Killian
What causes acute myelogenous syndrome?
Translocation, part of 22 moves to 9
