Non mendelian inheritance

Question 1

Give mechanism of non mendelian inheritance inheritance pattern and mechanism?

Answer 1

Incomplete Penetrance- Environmental factor and genetic modifiers to specific genetic traits

Genomic Imprinting- Variants from parents

Extranuclear Inheritance- mitochondrial mutations

Anticipation- Triplet repeat expansion

Complex-multi genic risk

Question 2

What is penetrance?

Answer 2

penetrance is the frequency with which a trait is manifested by individuals carrying the gene

Question 3

What is cystic fibrosis caused by?

Answer 3

caused by a mutation in CFTR (autosomal recessive)

Question 4

Describe genetic modifiers?

Answer 4

genes that have small quantitive effects on the level of expression of another gene
may involve polymorphism, maybe intra or extra genic

Question 5

What is genomic imprinting?

Answer 5

gene expressed from only one chromosome

parent of origin dependent

Question 6

Describe epigenetic modifications?

Answer 6

Heritable changes in gene function not explained by changes in DNA sequences

Question 7

What does methylation mean?

Answer 7

methylcystosine( mC) induces the structural adaptation of chromosomal region so as to perpetuate altered activity states- stops it being available for translation

Question 8

Give genetic mechanisms of imprinting disorders?

Answer 8

Deletions
Point mutations
Imprinting errors
Uniparental disomy

Question 9

Describe deletions outcome?

Answer 9

deletion of maternal copy of maternally expressed gene- no working copy of it
deletion of paternal copy of maternally expressed gene -no effect

Question 10

Describe uniparental disomy?

Answer 10

complete chromosome duplicated and therefore get 2 copies of some genes and 0 copies for others.

Question 11

Describe a gynogenic uniparental diploidy?

Answer 11

• 2 maternal genomes
• Mass of embryo
• Ovarian teratoma

Question 12

Describe an androgenic uniparental diploidy?

Answer 12

• 2 paternal genomes
• Mass of placenta
• Hydatidiform mole

Question 13

What is prader willi syndrome caused by?

Answer 13

caused by loss of paternal elements

Question 14

What is angelman syndrome caused by?

Answer 14

loss of maternal elements

Question 15

Why do we inherit mitochondria from mother?

Answer 15

few in sperm but degrade and arent used in creation of embryo

Question 16

Give features of the mitochondrial genome?

Answer 16

High mutation rate: 100-fold higher than the nuclear genome
Lack of efficient DNA repair system.
Lack of protective proteins, such as histones.
Damaged by reactive oxygen species (ROS), such as free radicals.

Question 17

What is homoplasmy?

Answer 17

all normal copies of mitochondrial genome

Question 18

What is heteroplasmy?

Answer 18

two or more mtdna with genetic alteration

Question 19

What do mitochondrial diseases typically affect?

Answer 19

tissues with high metabolic demand

Question 20

What is anticipation - triplet repeat expansion?

Answer 20

Disease presents at earlier age and/or increasing severity in succeeding generations.
e.g. Triplet repeat diseases
- Huntington’s disease
- Myotonic dystrophy (DM1)
- Fragile X syndrome

Question 21

Describe multigenic/ complex inheritance?

Answer 21

Complex inheritance involves multiple genes and environmental factors that influence the risk or development of a condition.

Multiple Low Penetrance Variants: These are genetic variants that each contribute a small amount to the risk of a condition, but none by itself causes the disease.

Rare High Penetrance Variants: These are less common genetic variants that, when present, significantly increase the risk of a condition (e.g., certain mutations in many genes causing similar symptoms in schizophrenia).

-environmental factors often significant

Question 22

What are the common conditions of multigenic/ complex inheritance?

Answer 22

Heart disease
Breast cancer
Autism