Genetics 2- Risk of Transmission of Genetic Disease

Question 1

Define monogenic gentic dieseases

Answer 1

Clear inheritance

No environmental influence

Rare

EXAMPLES: Huntingdon Disease, Cystic Fibrosis, Haemophilia.

Question 2

Define complex disorders

Answer 2

No clear inheritance

Environment essential

Common

EXAMPLES: Type 2 Diabetes, Schizophrenia, Crohn’s Disease

Question 3

What is Mendelian Inheritance

Answer 3

• The process whereby individuals inherit and transmit to their offspring one out of the two alleles present in homologous chromosomes.

Question 4

Define allele

Answer 4

• alternate forms of a gene or DNA sequence at the same chromosome location (locus).

Question 5

Define homologous chromosomes

Answer 5

matching (but non-identical) pair of chromosomes - one from each parent.

Question 6

What are mutations and polymorphisms

Answer 6

Mutation - any heritable change in the DNA sequence

Polymorphism - a mutation at a >1% frequency in a given population.

NOTE: Polymorphisms are usually still called mutations if they cause monogenic disease.

Polymorphisms may contribute to complex diseases.

Question 7

What are the different types of mutations

Answer 7

Types of Mutation:
Point Mutations (a single change in the DNA sequence): Missense - mutation means that the codon changes to      code for a different amino acid. 
Nonsense - mutation means that the codon codes for a stop codon so the polypeptide chain ends prematurely.  

Frame-shift Mutations:

  Insertion - insertion of an extra base will cause the 
  code to be shifted out of frame.  

  Deletion - deletion of a base

Question 8

5 Types of Mendelian Inheritance Patterns

Answer 8

Autosomal Dominant

Autosomal Recessive

X-linked Dominant (RARE)

X-linked Recessive

Mitochondrial

Question 9

What are autosomal dominant inhertiance patterns?

Answer 9

Autosomal Dominant
At least one affected parents
50% risk of child being affected

Autosomal Dominant Disease EXAMPLE: Huntingdon’s Disease

Question 10

What are autosomal recessive inhertiance patterns?

Answer 10

Autosomal Recessive

No affected parent

Usually no family history

25% risk of child being affected

50% chance of child being carrier

Autosomal Recessive Disease EXAMPLE: Cystic Fibrosis

Question 11

What are X-Linked Recessive inhertiance patterns?

Answer 11

No affected parents

Usually only males affected.

TRANSMITTED BY FEMALE CARRIER

Sons have a 50% risk of being affected

Daughters have a 50% chance of being a carrier

X-Linked Recessive Disease EXAMPLE: Haemophilia

Question 12

what are the 3 Molecular Mechanisms of Genetic Disease

Answer 12

Dominant Conditions - usually caused by gene mutations that result in toxic protein (e.g. HD) - effects of the mutated gene MASK the normal copy.

Recessive Conditions - caused by absence of functional protein (e.g. CF, Haemophilia) - effects of the mutated gene are only seen because the normal copy is absent.

Co-dominant Conditions - effects of both mutated and normal genes apparent in people with both e.g. Sickle Cell Trait