3 - Chromosomal abnormalities Flashcards
cytogenetics
The study of the structure and function of chromosomes
what is cytogenetics used for?
Used for the screening and diagnosis of inherited chromosomal disorders
Karyotype
a preparation of chromosomes arranged in size order
how to make a karyotype
blood sample treated with chemical that stimulates mitosis
another chemical added to stop mitosis at metaphase (double chromosomes but not separated yet)
what are the 3 ways to identify a chromosome?
- length
- banding pattern
- centromere placement
metacentric
centromere in centre
sub-metacentric
centromere is off-centre
acrocentric
centromere very close to end
What is karyotyping used for?
to detect changes in chromosome number and shape
polyploidy
Extra whole sets of chromosomes
aneuploidy
Some additional or missing chromosomes
monosomy
1 chromosome missing
trisomy
1 extra chromosome
what is aneuploidy caused by?
non-disjunction of homologous chromosomes
what is the only autosomal aneuploidy that permits survival into adulthood?
Down’s Syndrome
what is trisomy 21 commonly known as?
Down’s syndrome: 47,XX,+21
characteristics of down’s syndrome
- short
- sterile
- mental retardation
- heart defects
screening for chromosomal abnormalities
- amniocentesis and karyotyping
- blood tests
- ultrasounds
what is the only viable human monosomy?
Turner syndrome: 45,XO
characteristics of turner’s syndrome
- phenotypically female
- sterile, as sex organs immature
- treatment via oestrogen replacement
Klinefelter syndrome
47, XXY
characteristics of Klinefelter’s syndrome
- male with female characteristics
- tall
- sterile
– treated with testosterone replacement
What is a deletion mutation?
one nucleotide is taken away from a gene or DNA sequence
What is a duplication mutation?
When one or more bases are repeated
what is an inversion mutation?
when part of a chromosome breaks off and reattaches backwards
what is reciprocal translocation?
The breakage and rejoining of 2 non-homologous chromosomes, with a reciprocal exchange of the broken segments.
What is cri du chat syndrome?
absence of short arm of 5th chromosome
characteristics of cri du chat syndrome
- cat-like cry
- defects in larynx
- retardation
Prader-Willi Syndrome
Deletion in long arm of chr 15 (15q1.12)
- only occurs when the affected chromosome is inherited from the father, due to genomic imprinting
prader willi characteristics
- poor suckling reflex
- uncontrollable eating
- poor male sexual development
Angelman Syndrome
deletion of maternal chromosome 15
characteristics of angelman’s syndrome
- happy demeanor
- innapropriate outbursts of laughter
- mental retardation
which conditions are caused by translocations
familial down’s syndrome and chronic myelotic leukaemia
Familial Down’s Syndrome
- accounts for ~5% of Down’s cases
- Translocation carrier t(14;21): one of the chr 21’s is attached to one of the chr 14s
Chronic myelocytic leukaemia (CML)
- spontaneous, not heritable
- Occurs in 1 per 50-100,000 of the population, most common in middle-aged/elderly
- Accounts for 15-20% of all cases of leukaemia
what causes Chronic myelocytic leukaemia
22-9 translocation creating BCR-ABL fusion gene
BCR-ABL fusion gene
an oncogene that stimulates over-production of white blood cells
