Genetics

Question 1

Maternal imprinting

Answer 1

Gene when inherited from mother is silent.

eg. Prader-Willi
ie. Only children of affected fathers are affected.

Question 2

Paternal imprinting

Answer 2

Gene when inherited from father is silent.

eg. Angelman
ie. Only children from affected mothers are affected.

Question 3

Somatic mosaicism

Answer 3

Genetically different cell lines within an individual (may or may not involve germ cells).

Question 4

Germline (gonadal) mosaicism

Answer 4

Mutations for genetically different cell lines in germ cells, can be inherited and cause full phenotype in offspring.

Question 5

Chimerism

Answer 5

Two or more genetically different cell lines derived from two (or more) zygotes.

Question 6

X-linked recessive

Answer 6

No male-male transmission.

Males more likely to be affected.

Question 7

X-linked dominant

Answer 7

Males usually severely affected (usually lethal in pregnancy). Half of females affected.

Question 8

Mitochondrial mutation

Answer 8

Maternal transmission (only maternal mtDNA inherited).
Variable effects in different organs within family.

Question 9

Uniparental disomy

Answer 9

Duplication of one parent’s chromosome, other parent’s chromosome suppressed.
Causes autosomal recessive disease derived from single parent.

Question 10

Linkage disequilibrium

Answer 10

Tendency for alleles of genes / genetic markers to be inherited together in non-random fashion.
Genes close in chromosomal position (unlikely to separate in chromosome assortment or cross-over meiosis)

Question 11

Diseases with triplet repeat instability in maternal transmission

Answer 11

Myotonic dystrophy (DM1)
Fragile X (FRAX)
Spinocerebellar ataxia (SCA8)

Question 12

Diseases with triplet repeat instability in paternal transmission

Answer 12

Huntington (HTT)
Spinocerebellar ataxia (SCA1, SCA2, SCA7)

Question 13

45,X

Answer 13

Turner syndrome
Short stature
Broad chest, wide-spaced nipples
Neck webbing
Ovarian failure, pubertal delay

Question 14

47,XXY

Answer 14

Klinefelter syndrome
Primary hypogonadism - most common sex chromosome cause
Tall stature
Small testes
Azoospermia
Psychiatric and autism spectrum disorders

Question 15

47,XXX

Answer 15

Triple X syndrome
Tall
Small head
Premature ovarian failure
Developmental delay

Question 16

Genetic risk factors in diabetes

Answer 16

Offspring of affected father - T1DM increased risk

Offspring of affected mother - T2DM increased risk

Question 17

Monogenic inheritance

Answer 17

Phenotype due to inheriting one mutant gene

Question 18

Digenic inheritance

Answer 18

Phenotype due to mutation in two different genes

Question 19

Heterozygosity

Answer 19

Two different alleles for the same gene

Question 20

Allelic heterogeneity

Answer 20

Different mutations at same locus cause similar phenotype

Question 21

Locus heterogeneity (aka non-allelic heterogeneity)

Answer 21

Mutations in genes at different chromosomal loci cause similar phenotype

Question 22

Hemizygosity

Answer 22

Only one allele of gene is present

Question 23

Alpha thalassaemia

Answer 23

Impaired alpha globin chains, relative excess in beta globin chains
1 - Silent carrier
2 - Trait
3 - HbH disease
4 - Hydrops foetalis

Question 24

Most common cardiac abnormality in Turner’s syndrome

Answer 24

Bicuspid aortic valve

Question 25

Cause of male infertility in cystic fibrosis

Answer 25

Obstructive azoospermia
(Due to bilateral absent vas deferens)