6 Cytogenetic inheritance Flashcards
When in the cell cycle to cytogenetic techniques work?
Metaphase analysis is during mitosis.
Molecular techniques used in any phase.
How do cytogenetic abnormalities produce an abnormal phenotype? (5).
Dosage effect. Disruption of a gene. Effect due to parental origin. New position effect. Unmasking of recessive disorder.
Is a sex or autosomal chromosomal imbalance more sever?
Autosomal.
Differentiate between aneuploidy and polyploidy.
Aneu: gain a new copy of one chromosome.
Poly: gain a complete set.
Why does maternal age increase autosomal aneuploidy risk?
Unfavourable chiasmata distribution in foetus.
Deterioration of meiotic structures.
Clinical features of trisomy 21:
75% spontaneously abort.
Upward slanting eyes, small nose, low set ears, short neck, learning disabilities, single palmar crease, broad hands, wide sandal gap.
Clinical features of trisomy 21 in adulthood: (8).
Male infertility. Increased risk leukaemia. Alzheimers. Hypothyroid. Obesity, diabetes. Arthritis. Hearing loss. Seizures.
Which syndrome is the result of trisomy 18?
Self abortion rate?
Edward’s syndrome.
95% abort.
Which syndrome is the result of trisomy 13?
Self abortion rate?
Patau syndrome.
95% abort.
What is genotype of Turner’s syndrome?
45, X.
What is the genotype of Klinefelter’s syndrome?
47, XXY.
What does triploidy from either parental origin result in?
Paternal: large placenta, small growth delay.
Maternal: tiny placenta, significant growth delay.
What is a molar pregnancy?
Empty egg, so sperm doubles. Cystic placenta with no embryo.
Positive pregnancy test.
How does mosaicism occur?
Early cleavage error resulting in monosomy, disomy and trisomy.
What are the consequences of mosaicism? (3)
Variable phenotype + lethality.
Non-identical twin.
Lateral asymmetry.
What is a robertsonian translocation?
What are the risks of such a disorder?
Whole arm fusion of acrocentric chromosomes.
No phenotype risk. Reproductive risk.
What is the difference between a pericentric and paracentric inversion?
Peri is around the centromere.
Para is all on one side of the centromere.
Which is generally more serious: a deletion or a duplication of genetic information?
Deletion.
What are the clinical features of Edwards syndrome? (6 groups).
Microcephaly, severe mental retardation. Cleft lip + palate. Clenched hands, rocker bottom feet. Low birth weight. Short sternum. Congenital heart disease, kidney problems.
What are the clinical features of Patau syndrome? (6 groups).
Small at birth. Microcephaly, severe mental retardation. Holoprosencephaly (two hemisphere's don't form). Micropthalmia, cleft lip. Polydactyly. Heart defect.
What are the clinical features of Turner syndrome? (5).
No ovarian function.
Lymph obstruction: webbed neck, distal limb swelling. Short stature.
Aorta coarctation.
IQ reduction.
What are the clinical features of Kleinfelter syndrome? (4).
Infertility, hypogonadism.
Lack of 2o sex characteristics.
Accelerated growth - long arms + legs.
IQ normal.
