Genetic Basis of Disease

Question 1

Give examples of types of mutations.

Answer 1

(1) Point mutation (e.g. silent mutatino, mis-sense, non-sence)
(2) Insertion
(3) Deletion
(4) Duplication
(5) Frameshift mutation
(6) Inversion
(7) Translocation

Question 2

What is a gene?

Answer 2

A gene is a unit of DNA that codes for a specific protein.

Question 3

Differentiate between an exon and an intron.

Answer 3

exon: contains DNA code for the protein
intron: non-coding regions of a gene

Question 4

What is a codon?

Answer 4

A codon is a sequence of 3 nucleotides in mRNA.

Question 5

Define pleiotropy.

Answer 5

Pleiotropy refers to a phenomenon whereby one gene influences multiple phenotypic traits. [For example, the gene that influences melanin production can affect skin color, hair color, and eye color all at once.]

Question 6

Define penetrance.

Answer 6

Penetrance refers to the proporiton of individuals with a specific genetic mutation who actually show symptoms or traits of the associated condition.

Question 7

Give examples of penetrance.

Answer 7

Complete penetrance: Everyone with the mutation has the condition.
Incomplete (or Reduced) penetrance: Some people with the mutation may not show any signs of the condition, even though they carry the genetic mutation.

Question 8

Name four patterns of inheritance and give one example of each.

Answer 8

(1) Autosomal recessive: need two copies of the mutated gene from each parent. Examples: Cystic fibrosis, Sickle cell anaemia.

(2) Autosomal dominant: only need one copy of the mutated gene. Examples: Huntington’s disease, Marfan disorder.

(3) X-linked recessive: males need one mutated gene on the X chromosome and females need 2 to have the condition. Example: Hemophilia A.

(4) X-linked dominant: one mutated gene on the X chromosome is enough to cause the condition. Example; Fragile X syndrome.

Question 9

In what inheritance patterns are carriers present?

Answer 9

(1) Autosomal recessive
(2) X-linked

Question 10

Explain and give an example of multifactorial inheritance.

Answer 10

Multifactorial inheritance refers to the type of inheritance where multiple factors, both genetic and environmental, contribute to the development of a trait or disorder.
Examples: non-insulin dependent diabetes mellitus, obesity, NTD’s (neural tube defects), schizophrenia