Genetics Flashcards
What are the three different types of chromosomal abnormalities
Numerical, structural, and mutational
Define trisomy
Extra copy of chromosomes
Define monosomy
Only 1 chromosome present from a pair is present in cells
What is trisomy 21 known as
Down’s Syndrome
What is trisomy 13 known as
Patau Syndrome
What is trisomy 18 known as
Edward’s Syndrome
What is the result of non-disjunction
- Two gametes with disomy and 2 dull gametes (meiosis 1)
- 1 gamete with disomy, 1 gamete null, and 2 gametes normal (meiosis 2)
What are the features of Down Syndrome
- Low IQ (less than 50)
- Low muscle tone
- Short stature
- Flat nasal bridge
- Protruding tongue
What can Down syndrome cause
- Alzheimer’s disease in later life
- Higher risk of conditions e.g. epilepsy
What increases the risk of Down’s syndrome
Advancing maternal age
What are the chromosomal findings of Down’s syndrome
- Trisomy 21, non-dysjunction (95%), usually maternal origin
- Unbalanced Robertsonian translocation (4%)
- Mosaicism
What are the features of Patau Syndrome
Multiple dysmorphic features and mental retardation
What is the complication of Patau Syndrome
5% die within the first month and very few survive beyond first year
What are the chromosomal findings of Patau Syndrome
- Non-dysjunction (90%), maternal origin
- Unbalanced Robertsonian translocation (10%)
What does Edward’s Syndrome cause
Severe developmental problems with most patients dying within the first year, many within the first month
What are the features of Edward’s Syndrome
- Low birth weight
- Heart, resp, kidney, and GI conditions
What is monosomy 45 X known as
Turner’s Syndrome
What are the features of Turner’s Syndrome
- May be born with swollen hands and feet due to excess fluid but will resolve
- Neck webbing and widely spaced nipples
- Short stature and infertile
- Doesn’t affect intelligence or lifespan
Who can present with Turner’s Syndrome
Females only
What condition has 47, XXY
Klinefelter Syndrome
Who can present with Klinefelter Syndrome
Men only
What are the features of Klinefelter Syndrome
- Tall stature, long limbs
- Infertile, small testies, about 50% gynaecomastia
- Mild learning difficulties
What are the different types of structural abnormalities
- Translocations (reciprocal and Robertsonian)
- Deletions
- Insertions
- Inversions
Describe what is balanced translocation
2 different chromosomes exchange large sections of information with no DNA missing or any additional DNA
What is the outcome of reciprocal translocation
Meiosis can create:
- Normal gamete (inherit the two normal gametes) which results in a normal zygote
- Balanced gamete (inherit the two chromosomes that exhanged information) which results in a balanced carrier zygote
- Unbalanced gamete (inherit a normal and a translocated chromosome) which results in a partial trisomy and partial monosomy
Describe what Robertsonian translocation is
Involves the fusion of acrocenteric chromosomes (long Q arm which has normal coding DNA and a short P arm which has no coding DNA on it)
What is the effect of Robertsonian translocation
When the two acrocentric chromosomes undergo a fusion, they finish up with a Robertsonian translocation. The two Q arms fuse to present in one chromosome and the short P arms also form a new chromosome
What is the outcome of Robertsonian translocation
- Normal gamete which results in a normal zygote
- Balanced robertsonian translocation (only robertsonian translocation is inherited) which results in a balanced carrier
- Unbalanced robertsonian translocation (a robertsonian translocation chromosome and a normal chromosome is inherited) which results in trisomy or monosomy (normal chromosome inherited on its own)
Describe the structural abnormality of deletion
DNA gets broken down in chromosomes which is normal but becomes abnormal if it is not repaired
Describe the structural abnormality of inversion
A large piece of DNA is reversed (paracentric inversion is away from the centromere and pericenteric inversion is at the centromere)
