Chromosomes Flashcards
Which letter stands for long and short arm?
P = short Q = long
What do acrocentric and metacentric mean?
Acrocentric = centromere near the end of a chromosome
Submetacentric = in the middle of acro and meta
Metacentric = centromere in the centre of a chromosome
What is significant about chromosome numbers?
1 to 22 is largest to smallest
What is Giemsa?
A DNA-binding dye giving characteristic light/dark banding (G-banding) on chromosomes
What does a light band represent vs dark band in G-staining?
Active transcription occurring at light bands (DNA looser, euchromatin)
Inactive areas stain dark
What is FISH?
Diagnostic tool for when you KNOW what you’re looking for
Fluorescent In Situ Hybridisation
Fluorescently labelled ssDNA probe anneals to complementary target sequence in metaphase spread
What is array CGH, and what is it used for?
CGH = comparative genome hybridisation
To detect regions of gene amplification/loss, especially in cancer (unusual chromosome pattern) and dysmorphic individuals (usually due to chromosomal abnormality)
Test DNA labelled green
Normal DNA labelled red
Amplification = green Loss = red
Why is an array CGH used over FISH and other tools?
Very high resolution
Can detect dosage abnormalities that are not visible cytogenetically
Abnormalities not always relevant - check by looking at parents
How is array CGH carried out?
Control DNA (green) and Patient DNA (Red) applied to microarray, containing lots of wells with probes for different genes in it
DNA gain = red
DNA loss = green
DNA same = yellow
Fluorescent signals measured by microarray scanner - computer then makes a plot and can compare to a genome online
How is sex determined? Evidence for this…
Female is default
If Y chromosome is present, then male develops
Y chromosome has sex-determining region called SRY
Evidence:
- XX males had SRY gene present
- XY females have SRY deletion
- XX mice with SRY inserted became males
What is SRY?
Transcription regulator that determines maleness
What does SRY do?
Stimulates transcription of genes leading to development of testis from Wolffian ducts (Testosterone release)
Sertoli cells in testis release Mullerian Inhibitory Factor which inhibits female gentalia production (which develops from Mullerian ducts)
What is the Lyon hypothesis relating to X chromosomes?
That early in embryonic life, paternal or maternal X is randomly inactivated - propagates through mitosis
Is X-inactivation always random, complete and permanent?
No
Random mostly, though structurally abnormal X usually inactivated preferentially
Complete mostly, though some genes escape inactivation
Permanent mostly, though reversed in germ cell development
What is a Barr Body?
Darkly stained mass found close to nuclear membrane representing inactivated X chromosome
What about 2?
1
Turner syndrome
- features
- karyotype
Features:
- wide neck
- short stature
- wide carrying angle (hands point outwards when hanging by sides)
- shield chest
- primary amenorrhoea (no menstrual cycle)
- infertility
- cardiac abnormalities (coarctation of aorta)
Karyotype
-45X
Kleinfelter Syndrome:
- features
- karyotype
Features
- tall stature
- mildly impaired IQ
- breast development
- testicular atrophy
- feminised physique
- not much male pubic hair
Karyotype
-47XXY
Triple X:
- features (think supermodel lol)
- karyotype
Features:
- tall
- feminine
- slight intellectual impairment
Karyotype:
-47XXX
XYY features and karyotype
Features
-associated with criminal tendencies
Karyotype
-47XYY
Down syndrome
- Features
- Karyotype
Features
- almond shaped eyes
- single palmar crease
- widened sandal gap (great toe gap)
- tongue sticking out due to —> poor muscle tone
- sometimes intellectual diasbility
- cardiac problems (septal defects)
- thyroid problems
- develop Alzheimer’s
- Liquid tumours (lymphomas/leukaemias)
Karyotype
-Trisomy 21
What is it called when an extra chromosome ends up in a gamete?
Non-dysfunction event
Patau syndrome
- features
- karyotype
Features
- clefting
- finger and toe abnormalities
- don’t usually survive first year
- severe intellectual disability
- heart defects
- scalp defects
Karyotype
-trisomy 13
Edward’s Syndrome
- features
- karyotype
Features
- severely clenched fingers
- protuberant back of head
- ‘rocker-bottom’ feet
- severe intellectual disability
- cardiac abnormalities
Karyotype
-trisomy 18
