1- Genetics Flashcards
How do autosomal recessive conditions typically present across generations?
They can skip generations and are more common in consanguineous families.
What is the recurrence risk for offsping of two autosomal recessive carriers?
25%
In X-linked dominant inheritance, who is more severely affected: males or females?
Males
Can X-linked dominant traits be passed from father to son?
No, there is no male-to-male transmission.
What is the chance of an affected female passing on an X-linked dominant condition to her child?
50%
What causes Down syndrome in 95% of cases?
3 free copies of chromosome 21 (Trisomy 21), mostly of maternal origin during meiosis I.
What are key clinical features of Down syndrome?
Learning difficulties, flat facial profile, congenital heart defects, GI problems, early Alzheimer’s.
What is mosaicism?
Presence of two or more genetically different cell lines in the same person.
What is a translocation?
A chromosomal abnormality where a piece of one chromosome attaches to another.
What is the difference between balanced and unbalanced translocations?
Balanced means no genetic material is lost; unbalanced means there is a gain or loss of material, often inherited.
What chromosomal abnormality causes Turner Syndrome?
Complete or partial deletion of one X chromosome.
What are features of Turner Syndrome?
Short stature, infertility, coarctation of the aorta, learning difficulties, low IQ.
What is the karyotype of Klinefelter Syndrome?
47,XXY
What are features of Klinefelter Syndrome?
Tall stature, hypogonadism, infertility, learning/psychological difficulties.
What is the typical presentation of 47,XYY syndrome?
Tall males with normal fertility, occasionally mild learning difficulties.
What is the outcome for females with Triple X (Trisomy X)?
Usually normal development and fertility, with possible learning or motor difficulties.
What is the genetic basis of Williams-Beuren Syndrome?
Hemizygous deletion of 1.5–1.8 Mb on chromosome 7.
What are features of Williams Syndrome?
Supravalvular aortic stenosis, learning difficulty, distinctive facial features, short stature.
What causes Cri-du-chat Syndrome?
Terminal deletion of the short arm of chromosome 5.
What are features of Cri-du-chat Syndrome?
Microcephaly, round face, hypotonia, developmental delay, cat-like cry.
What gene is affected in Fragile X Syndrome?
FMR1 gene on the X chromosome.
What type of mutation is seen in Fragile X?
CGG trinucleotide repeat expansion (50–200 times).
Who is more severely affected by Fragile X Syndrome?
Males, as they have only one X chromosome.
What are features of Fragile X Syndrome?
Macrocephaly, distinctive face, autism traits, seizures, learning difficulties.
What gene is involved in Rett Syndrome?
MECP2 gene on the X chromosome.
In whom does Rett Syndrome typically occur?
Females; usually lethal in males unless they have Klinefelter’s.
What are signs of Rett Syndrome?
Arrested development (6–18 months), regression, neurodevelopmental delay.
What is genetic imprinting?
Differential expression depending on whether the gene is inherited from the mother or father.
What causes Angelman Syndrome?
Maternal deletion of chromosome 15 or mutations in the UBE3A gene.
What are features of Angelman Syndrome?
Happy demeanor, learning and motor delays, speech difficulties.
What causes Prader-Willi Syndrome?
Paternal deletion or uniparental disomy of chromosome 15.
What are features of Prader-Willi Syndrome?
Hypotonia, obesity, short stature, motor/speech delays.
What is the purpose of a karyotype?
To examine the number and structure of chromosomes.
What does FISH stand for and do?
Fluorescence in situ hybridization; detects chromosomal abnormalities.
What is Sanger sequencing?
The gold standard method for sequencing small stretches of DNA.
What is Next Generation Sequencing (NGS)?
A modern method that allows sequencing of large amounts of DNA quickly.
What are common sequencing targets?
Gene panels, whole exome sequencing, whole genome sequencing.
What is a de novo mutation?
A new mutation not inherited from either parent.
Why are many pregnancies with chromosomal abnormalities non-viable?
Severe abnormalities often lead to miscarriage or early fetal loss.
What should you explore if a child presents with developmental delay and dysmorphic features?
Consider chromosomal analysis (e.g., karyotype, FISH, NGS).
