6 Cytogenetic inheritance

Question 1

When in the cell cycle to cytogenetic techniques work?

Answer 1

Metaphase analysis is during mitosis.

Molecular techniques used in any phase.

Question 2

How do cytogenetic abnormalities produce an abnormal phenotype? (5).

Answer 2

Dosage effect.
Disruption of a gene.
Effect due to parental origin.
New position effect.
Unmasking of recessive disorder.

Question 3

Is a sex or autosomal chromosomal imbalance more sever?

Answer 3

Autosomal.

Question 4

Differentiate between aneuploidy and polyploidy.

Answer 4

Aneu: gain a new copy of one chromosome.
Poly: gain a complete set.

Question 5

Why does maternal age increase autosomal aneuploidy risk?

Answer 5

Unfavourable chiasmata distribution in foetus.

Deterioration of meiotic structures.

Question 6

Clinical features of trisomy 21:

Answer 6

75% spontaneously abort.
Upward slanting eyes, small nose, low set ears, short neck, learning disabilities, single palmar crease, broad hands, wide sandal gap.

Question 7

Clinical features of trisomy 21 in adulthood: (8).

Answer 7

Male infertility.
Increased risk leukaemia.
Alzheimers.
Hypothyroid.
Obesity, diabetes.
Arthritis.
Hearing loss.
Seizures.

Question 8

Which syndrome is the result of trisomy 18?

Self abortion rate?

Answer 8

Edward’s syndrome.

95% abort.

Question 9

Which syndrome is the result of trisomy 13?

Self abortion rate?

Answer 9

Patau syndrome.

95% abort.

Question 10

What is genotype of Turner’s syndrome?

Answer 10

45, X.

Question 11

What is the genotype of Klinefelter’s syndrome?

Answer 11

47, XXY.

Question 12

What does triploidy from either parental origin result in?

Answer 12

Paternal: large placenta, small growth delay.
Maternal: tiny placenta, significant growth delay.

Question 13

What is a molar pregnancy?

Answer 13

Empty egg, so sperm doubles. Cystic placenta with no embryo.

Positive pregnancy test.

Question 14

How does mosaicism occur?

Answer 14

Early cleavage error resulting in monosomy, disomy and trisomy.

Question 15

What are the consequences of mosaicism? (3)

Answer 15

Variable phenotype + lethality.
Non-identical twin.
Lateral asymmetry.

Question 16

What is a robertsonian translocation?

What are the risks of such a disorder?

Answer 16

Whole arm fusion of acrocentric chromosomes.

No phenotype risk. Reproductive risk.

Question 17

What is the difference between a pericentric and paracentric inversion?

Answer 17

Peri is around the centromere.

Para is all on one side of the centromere.

Question 18

Which is generally more serious: a deletion or a duplication of genetic information?

Answer 18

Deletion.

Question 19

What are the clinical features of Edwards syndrome? (6 groups).

Answer 19

Microcephaly, severe mental retardation.
Cleft lip + palate.
Clenched hands, rocker bottom feet.
Low birth weight.
Short sternum. 
Congenital heart disease, kidney problems.

Question 20

What are the clinical features of Patau syndrome? (6 groups).

Answer 20

Small at birth.
Microcephaly, severe mental retardation.
Holoprosencephaly (two hemisphere's don't form).
Micropthalmia, cleft lip.
Polydactyly.
Heart defect.

Question 21

What are the clinical features of Turner syndrome? (5).

Answer 21

No ovarian function.
Lymph obstruction: webbed neck, distal limb swelling. Short stature.
Aorta coarctation.
IQ reduction.

Question 22

What are the clinical features of Kleinfelter syndrome? (4).

Answer 22

Infertility, hypogonadism.
Lack of 2o sex characteristics.
Accelerated growth - long arms + legs.
IQ normal.