Genetics

Question 1

How many chromosomes do humans have and what are they?

Answer 1

23 pairs = 46 chromosomes.
44 autosomes, 2 sex chromosomes
XX=Female, XY=Male

Question 2

What does it mean if a genetic condition is Mendelian inheritance? 2 examples?

Answer 2

• simple inheritance pattern. Disease is caused by a single abnormal gene on one of the non-sex chromosomes
• Huntingtons (dominant), Cystic fibrosis (recessive)

Question 3

What is genetics of Klinefelter syndrome?

Answer 3

MALE has an additional X chromosome, 47XXY (rarely 48 XXXY)

Question 4

Features of Klinefelter

Answer 4

Usually normal until puberty:

• Infertility, reduced libido, small testes
• taller height, wider hips
• Gynaecomastia (breasts)
• Subtle learning difficulties

Question 5

Management of Klinefelter

Answer 5

Cant treat underlying cause.

- testosterone injections, IVF, breast reduction to help with features

Question 6

Genetics of Turner syndrome

Answer 6

FEMALE has a single X chromosome, making them 45XO. O = empty space where chromosome should be.

Question 7

Features of Turner

Answer 7

• neonates: lymphoedema of hands and feet, congenital heart defects (coarct.)
• Short stature, webbed neck, obesity,
• Late puberty, infertility
• ptosis + epicanthic folds, cubitus valgus

Question 8

What is cubitus valgus

Answer 8

refers to an abnormal feature of the elbow. When the arm is extended downwards with the palms facing forward, the angle of the forearm at the elbow is exaggerated, angled away from the body

Question 9

Mx of Turners

Answer 9

There is no way to treat the underlying genetic cause of Turner syndrome. Treatment aims to help with the symptoms of the condition:

• Growth hormone therapy
• Oestrogen and progesterone replacement can help establish female secondary sex characteristics, regulate the menstrual cycle and prevent osteoporosis
• Fertility treatment

Question 10

Genetics of Down syndrome

Answer 10

• 3 copies of chromosome 21 (autosomal).

Question 11

Features of Downs

Answer 11

• hypotonia (but hyperflexibility)
• single palmar crease
• prominent epicanthic folds
• Brachycephaly (small head with flat back)
• others: short stature, flattened face, protruding tongue, congenital heart defects
• delayed motor development, learning difficulties, epilepsy

Question 12

Immediate complications of Downs

Answer 12

Duodenal atresia, congenital heart disease

Question 13

Mx of Downs

Answer 13

• multidisciplinary team (start with this in exam)

- occupational, speech and language, physio, paeds, cardiologist…

Question 14

Genetics of Edwards

Answer 14

Trisomy 18

Question 15

Px of Edwards

Answer 15

• most die in infancy
• congenital heart defects, renal malformations, neurological problems
• neonatal features: growth restriction, prominent occiput, overlapping fingers, small mouth and chin

Question 16

Genetics of Patau’s

Answer 16

Trisomy 13

Question 17

Px of Patau’s

Answer 17

• most never survive till term
• structural defect of brain, congenital heart defects, cleft lip and palate
• small eyes, microcephaly, polydactyl

Question 18

Genetics of Fragile X syndrome

Answer 18

• mutation in FMR1 gene on X chromosome

- males always affected but females can vary in how affected as have a spare normal copy on other X chromosome.

Question 19

Features of Fragile X

Answer 19

• Intellectual disability
• Long, narrow face and Large ears
• Large testicles
• ADHD, anxiety, autism, seizures

Question 20

3 patterns of inheritance in X-linked recessive

Answer 20

1. Affected fathers cannot pass X-linked recessive traits to sons because they give Y chromosome to son
2. X-linked recessive traits more commonly expressed in males. Only have 1 X chromosome, females have 2 (so would need 2 mutations).
3. X-linked recessive tend to skip generations. (all daughters of an affected man will obtain his mutated X, and will then be either carriers or affected themselves depending on the mother. The resulting sons will either have a 50% chance of being affected (mother is carrier), or 100% chance (mother is affected).)