Chromosomal abnormalities case studies

Question 1

Jacob’s syndrome

Chromosomal abnormality

Answer 1

• Male offspring receives an extra copy of the Y chromosome from father, resulting in XYY genotype
• Not inherited, but occurs due to the random attribution of an extra Y chromosome to a sperm during spermatogenesis (meiosis II)
• Low frequency of 1 in 1000 births
• Mild effects on the individual: increased risk of comorbid conditions like asthma, autism, and learning difficulties, as well as taller than average height and large head size. May cause infertility
• Condition is not hereditary

Question 2

Triple X syndrome

Chromosomal abnormality

Answer 2

• Genotype: XXX
• Caused by a random error in cell division, usually the non-disjunction of the X chromosome in either the mother or father
• Mild effects, including taller than average height, kidney problems, and flat feet. May cause intellectual disabilities or behavioural problems
• For the most part, the effects of Triple X syndrome are not profound because X-inactivation mechanism deactivates the other 2 X chromosoes in females with this condition
• Condition is not hereditary