Patterns of Inheritence

Question 1

What type of inheritence pattern is Familial Hypercholesterolemia, Huntington’s disease Neurofibromatosis and Marfan syndrome?

Answer 1

Autosomal Dominant - Affecting Structural genes typically.

Question 2

Name some autosomal dominant Conditions

Answer 2

Familial Hypercholesterolemia, Huntington disease, Marfan syndrome, Neurofibromatosis.

Question 3

Describe Autosomal Dominant inheritence

Answer 3

Affected individuals have an affected parent.
Either sex is affected.
Variable to late onset typically.

Question 4

What type of inheritance pattern do Sickle cell anaemia, Cystic Fibrosis, Phenylketonuria (PKU) and Kartagener syndrome all have?

Answer 4

Autosomal Recessive - Affecting genes encoding for enzymes.

Question 5

What conditions have a Autosomal Recessive Inheritance pattern?

Answer 5

Sickle cell Anaemia, Phenylketonuria, Kartagener syndrome and Cystic Fibrosis.

Question 6

Describe Autosomal Recessive Inheritence

Answer 6

Unaffected parents, Either sex is affected, Early/uniform onset, often for catalytic proteins,

Sometimes occurs in consanguity (incest)

Question 7

What do Fragile X syndrome and Hypophosphatemic rickets (vitamin D resistant rickets) have in common?

Answer 7

X-Linked Dominant disorders

Question 8

Describe the inheritence of X-lnked Dominant disorders

Answer 8

Males cannot pass onto sons.

Mothers transmit to 50% of offspring. Fathers to all daughters.

Question 9

What type of inheritence is Duchenne Muscular dystrophy, G6PD deficiency, Lesch Nyhan syndrome, Ornithine transcarbamyase deficiency, Haemophilia A and B?

Answer 9

X-linked Recessive

Question 10

What is a sign of Mitochondrial inheritence?

Answer 10

Transmitted through mothers,
Variable expression,
Mitochondrial myopathies –> ragged red fibres on muscle biopsy.

Question 11

Define Codominance

Answer 11

Both alleles contribute to phenotye.

Question 12

Examples of codominant conditions?

Answer 12

Blood groups A, B and AB,

Alpha-1-antitrypsin dificiency

Question 13

What is Variable expressivity?

Answer 13

Phenotype varies among individuals with same genotype.

Question 14

Examples of variable expressivity.

Answer 14

Neurofibromatosis type 1, patients may have varying disease.

Question 15

What is Incomplete Penetrance?

Answer 15

Mutant genotype may not produce a mutant phenotype.

Question 16

Example of incomplete penetrance?

Answer 16

BRCA 1 gene for breast cancer increases chances to 60% - not 100%.

Question 17

What is Pleiotropy?

Answer 17

One gene contributes to multiple phenotypic effects.

Question 18

Examples of Pleiotropy?

Answer 18

Untreated Phenylketonuria leads to light skin, intellectual disability, musty smell.

Question 19

What is anticipation?

Answer 19

Increased severity of disease or earlier onset in succeding generations. HD.

Question 20

What is Loss of Heterozygosity?

Answer 20

If patient inherits or develops a mutation in a TS gene, the complementary allele must acquire a mutation before cancer develops.

Question 21

Examples of a loss of heterzygosity?

Answer 21

p53 and Retinoblastoma genes.

Question 22

What is a Dominant negative mutation?

Answer 22

Heterozygote produces nonfunctioning altered protein that prevents normal gene product formation or function.

Question 23

What is a Linkage disequillibrium?

Answer 23

Tendancy for two allels at 2 linked loci to occur together more or less often than expected by chance.

Question 24

What is Mosicism?

Answer 24

Presence of genetically distinct cell lines in the same individual.
Somatic - where the mutation arises from mitotic errors after fertilisation and occurs throughout tissues.
Gonadal - Mutations occur in sperm of egg cells but not all.

Question 25

Example of Mosaicism

Answer 25

McCune-Albright syndrome - Mutation affecting G-protein linked signalling.

Question 26

What are some signs of McCune-Albright syndrome?

Answer 26

Unilateral cafe au lait spots, polyostotic fibrous dysplasia, precocious puberty, endocrine abnormalities.

Question 27

What is Locus heterogenecity?

Answer 27

Mutations at different locations produce a similar phenotype. Albinism

Question 28

What is Allelic heterogenecity?

Answer 28

Different mutations at the same locus lead to the same phenotype. Example is Beta-Thalassaemia.

Question 29

What is Heteroplasmy?

Answer 29

Presence of both normal and mutated mtDNA lead to variable expression in mitochondrially inherited disease.

Question 30

What is Uniparental disomy?

Answer 30

Offspring recieves 2 copies of a chromosome from one parent and no copies from the other. Typically normal phenotype but can manifest as affected with recessive disorder found in one parent.

Question 31

Heterodisomy is where there is an error with what?

Answer 31

Meiosis I.

Question 32

Isodisomy is where there is an error where?

Answer 32

Meiosis II or postzygotic chromosomal duplication of one set and loss of the other.

Question 33

Prader-Willi syndrome and Angelman syndrome both have what in common?

Answer 33

Deletion of genes on chromosome 15, Typically brought out due to Maternal or paternal imprinting respectively.