1: Modes of Inheritance

Question 1

6 different modes of inheritance

Answer 1

autosomal recessive
autosomal dominant
x-linked dominant
x-linked recessive
mitochondrial
y-linked

Question 2

Characteristics of autosomal dominant inheritance

Answer 2

heterozygote - two different alleles at one locus
dominance expressed in phenotype

Question 3

Inheritance pattern of autosomal dominant characteristics

Answer 3

single gene/allele disease
several generations affected - vertical pedigree pattern
M&F equally affected

Question 4

Consequences of Autosomal dominant inheritance

Answer 4

gain-of-function (for mutated protein)
dominant negative effect (mutated allele interferes with wild type)
insufficient (levels of protein being made)

Question 5

Complicating factors of autosomal dominant inheritance

Answer 5

Age of onset

Question 6

Characteristics of autosomal recessive inheritance

Answer 6

• Homozygous genotype needed for expression
• mainly deletions = loss of function

Question 7

Inheritance pattern of autosomal recessive inheritance

Answer 7

parents and children of affected individual usually unaffected
siblings affected - horizontal pedigree pattern
M&F equally affected

Question 8

Genes of a carrier of an autosomal recessive condition

Answer 8

single copy of gene lost
one copy sufficient to maintain normal function

Question 9

What is consanguinity

Answer 9

marrying and having children with those of shared DNA

Question 10

What can consanguinity lead to

Answer 10

increased risk of autosomal recessive diseases

Question 11

Inheritance pattern of X-linked dominant conditions

Answer 11

Autosomal dominant pattern
Affected father = all daughters no sons affected

Question 12

Example of X-linked dominant condition

Answer 12

X-linked hypophosphatemia

Question 13

Consequences of X-linked dominant conditions

Answer 13

Milder and more variable conditions in females - due to X inactivation

Question 14

Inheritance pattern of X-linked recessive conditions

Answer 14

mainly males affected - dominant
females can be carriers
affected males can have affected maternal uncles
parents + children commonly unaffected
Brother of affected son 1 in 2 risk of condition, sister 1 in 2 chance being carrier
all daughters of affected male carriers, all sons healthy

Question 15

Examples of X-linked recessive conditions

Answer 15

Haemophilia
Fabrys disease

Question 16

Inheritance pattern of Y-linked inheritance

Answer 16

only males affected
all sons from affected father affected
vertical pedigree pattern

Question 17

Examples of Y-linked conditions

Answer 17

Retinitis pigmentosa Y-linked

Question 18

How does mitochondrial inheritance arise

Answer 18

Mitochondrial proteins encoded by mitochondrial nuclear genes
Mutations in genes cause most mitochondrial diseases
ALL mitochondria maternally inherited - mendelian/sex chromosome linked inheritance
Vertical pedigree pattern - children of affected woman all affected, children of affected man unaffected

Question 19

Disease variability in mitochondrial inheritance

Answer 19

Variable within families
Heteroplasmy - mitochondria hhave many copies of genome- some muatant

Question 20

Example of Mitochondiral inherited condition

Answer 20

Lebers hereditary optic neuropathy