Genetic basis of complex inheritance

Question 1

what are non-mendelian inheritance features?

Answer 1

1-Do not follow law of dominance
2-Do not follow law of segregation- alleles from each parent will separate during gamete formation
3-Do not follow law of independent segregation: alleles for 2 separate genes will be inherited independently

Question 2

Incomplete penetrance

Answer 2

Due to:

• Genetic modifiers: genes which modify the expression of other genes
• Environment

Question 3

Penetrance

Answer 3

The frequency with which a trait is manifested by the individuals carrying that trait
Risk of malignant/Risk of wild type

Question 4

Genomic imprinting

Answer 4

-When one parent is dependent on origin of trait
-Chromosome only active on one parent
Caused by:
-Epigenetic modifications- when changes in gene function cannot be explained through DNA mutation

-Uniparental disomy:
Both copies of one chromosome from 1 parent
Gynogenic: both copies from mother
Androgenic: both copies from father

Question 5

Mitochondria inheritance

Answer 5

Based on maternal inheritance.
Paternal mitochondria are destroyed inside fertilised egg.
Mitochondrial DNA is a hotspot for mutations:
-No DNA repair genes
-No histones for protection
-Can be damaged by 02 species
Homoplasmy: all copies of mitochondrial DNA is the same in a cell
Heteroplasmy: copies of mitochondrial DNA are different in a cell

Question 6

Anticipation

Answer 6

When disease presents at an earlier age and/or with increasing severity in suceeding generations.
Related to triple repeat diseases.

Question 7

Anticipation related diseases

Answer 7

Huntingtons
Myotonic dystrophy
Fragile-X syndrome
Triple repeat diseases

Question 8

Mitochondrial inheritance related diseases

Answer 8

Leigh’s syndrome
MERRF
MELAS
LHON-loss of central vision

Question 9

Genetic imprinting related diseases

Answer 9

BOTH DUE TO IMPRINTING IN 15q11-15q13
1-Angelmans -parental disomy
-epilepsy
-metal retardation 
-awkward gait
-inappropriate laughter 
2-Prader-willis- maternal disomy 
-mental retardation
-hypotonia-reduced muscle tone
-short stature 
-marked obesity

Question 10

Incomplete penetrance related diseases

Answer 10

Cystic fibrosis- CTFR gene

Breast cancer/ovarian cancer - BRCA1/2