Session 10

Question 0

Describe the chromosomal basis of sex determination

Answer 0

Male: XY
Female: XX

Question 1

Explain how the genetic information in a cell is organised as chromosomes

Answer 1

Chromosomes –> solenoid –> beads on a string –> DNA around histones

Question 2

Describe numerical and structural chromosome abnormalities and their significance

Answer 2

Numerical:
Polyploidy (triploidy, tetraploidy)
Aneuploidy (monosomy, trisomy)
Structural:
Balanced (the exchange or rearrangement of genetic material does not cause any missing or extra genetic information)
Unbalanced (cause missing or extra genetic information)

Question 3

Recognise, comprehend and apply chromosome nomenclature

Answer 3

Normal female - 46,XX
Normal male - 46,XY
+/- extra or missing entire chromosome

Question 4

Outline the reasons for referral of patients for karyotyping

Answer 4

Pre-natal screening - Down’s syndrome (especially in raised maternal age >35), family history of chromosomal abnormalities , abnormal ultrasound scan of foetus
Birth defects - malformations, mental or developmental impairment
Abnormal sexual development (Turner syndrome, Kleinefelter syndrome)
Infertility
Recurrent foetal loss
Leukaemia and related disorders

Question 5

Recognise the importance of fluorescent in situ hybridisation (FISH) in the detection of chromosome abnormalities

Answer 5

Detection is in situ by hybridisation of a fluorescently labelled probe