The Genetic Basis of Complex Inheritance - Non-Mendelian Inheritance

Question 1

What are the three laws of Mendelian Inheritance?

Answer 1

The Law of Dominance.

The Law of Segregation.

The Law of Independent Assortment.

Question 2

What is Non-mendelian Inheritance?

Answer 2

Does not fit in with Mendelian’s Law
e.g.
Gene conversion. Intermediate phenotype

Genetic material from only one parent?

Question 3

What is the mechanism for the following Inheritance patterns : Incomplete Penetrance

Genomic Imprinting

Extranuclear Inheritance

Anticipation

Answer 3

Environmental factor
Genetic Modifiers

Variants from parents

e. g. Mitochondria mutations
e. g. Triplet repeat expansion

Question 4

What is penetrance?

Answer 4

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

Compares risk of the same disease between different mutations

Question 5

What else apart from the CTFR mutation is responsible for the severity of CF in organs?

Answer 5

Genetic modifiers : Genes that have small quantitative effects on the level of expression of another gene.

May involve polymorphism.

Environment factors:
Lifestyle, Diet, Smoke, Alcohol, Drug,
Stress, Air pollution, Chemicals,
Infection, etc.

Question 6

What are the effects of CF?

Answer 6

Sinusitis

Lungs - Sticky mucus build up, bacterial infection and widened airways

Skin - sweat glands produce salty sweat

Liver - blocked biliary ducts

Pancreas - Blocked pancreatic ducts

Intestines - Cannot fully absorb nutrients

Reproductive organs - complications

Question 7

What is responsible for the rapid increase in prevalence of diabetes in the pacific region

Answer 7

Not merely genetic factors

obesity, unhealthy diets, and physical inactivity are also responsible

Question 8

What is genomic imprinting?

Answer 8

When genes are altered / shut off during the production of gametes

Question 9

What is Bi-allelic?

Answer 9

Same allele is turned on in both chromosomes from each parent?

Question 10

What is mono-allelic?

Answer 10

Gene is only turned on from one of the parents chromosomes

Question 11

What is the expression of genetic disease like in imprinted DNA?

Answer 11

Higher because there is only only copy of the gene

Question 12

What are Epigenetic modifications?

Answer 12

Heritable changes in gene function that cannot be explained by changes in DNA sequences

Question 13

What is Uniparental disomy?

Answer 13

Inheritance of a chromosome pair from one parental origin, because genes can be turned off there is a high risk of genetic mutation?

Question 14

What are the three sources of UPD?

Answer 14

Trisomy rescue, Monosomy rescue, Mitotic error (non-disjunction or Duplication)

Question 15

What is the result of uniparental diploidy?

Answer 15

Gynogenic

• 2 maternal genomes
• Mass of embryo
• Ovarian teratoma

Androgenic

• 2 paternal genomes
• Mass of placenta
• Hydatidiform mole

Question 16

What is responsible for Angelman UPD?

Answer 16

Paternal UPD

Question 17

What is responsible for Prader - Willi syndrome?

Answer 17

Maternal UPD

Question 18

Describe the DNA of mitochondria

Answer 18

Circular form
Lack of efficient DNA repair system.
Lack of protective proteins, such as histones.
Damaged by reactive oxygen species (ROS), such as free radicals.

Question 19

Describe the incidence of mutations of Mitochondria

Answer 19

100-fold higher than the nuclear genome.

Question 20

What is polyploidy?

Answer 20

up to thousands mitochondria per cell.

2 - 10 copies per mitochondrion.

Question 21

What is Homoplasmy?

Answer 21

A eukaryotic cell whose copies of mitochondrial DNA are all identical. When in normal and healthy tissues, all cells are homoplasmic.

Question 22

What is Heteroplasmy?

Answer 22

(two or more mtDNA)

Question 23

What does mitochondrial Disease affect?

Answer 23

Tissues with high metabolic demand

Question 24

What is a three parent baby?

Answer 24

Nucleasr DNA from one woman, plus the mitochondrial DNA from another woman, plus the fertilisation by a male

Question 25

What are triplet repeat diseases?

Answer 25

Diseases whereby a triplet repeat is repeated moreso than normal, Hungtington’s disease

Question 26

Define anticipation

Answer 26

Anticipation:

Disease presents at earlier age and/or increasing severity in succeeding generations

Question 27

Give examples of diseases that are spotted in earlier generations and increase with severity in later ones

Answer 27

Hungtington’s disease
Myotonic dystrophy
Fragile X syndrome

Question 28

What is the source of mitochondrial disease?

Answer 28

Form of maternal inheritance - mitochondrial DNA comes from the mother

Question 29

What type of disorder is cystic fibrosis?

Answer 29

Autosomal recessive disorder

Caused by faulty 7q31 gene

Question 30

How does the affected CTFR gene result in the condition?

Answer 30

Chloride channel responsible for removing chlorine from the cell is absent

Sticky mucus build up on the outside of the cell because this protein is absent

Question 31

Describe the disorder of Myotonic dystrophy

Answer 31

Autosomal dominant disorder

Question 32

What is the effect of

Answer 32

Severe distal muscle weakness and learning disabilities

Age of onset decreases with successive generations

Question 33

Describe the disorder of duchenne’s muscular dystrophy

Answer 33

X-linked recessive

Question 34

Where is the mutation in duchennes musculr dystrophy?

Answer 34

In the dystrophin gene

Question 35

What is the effect of duchennes muscular dystrophy?

Answer 35

Weakness of proximal muscle (close to the trunk of the body)

Delay in walking
Death at around 20 years

Question 36

What are the three mechanisms for epigenetic modifications?

Answer 36

DNA methylation, histone modification and non-coding RNA (ncRNA)-associated gene silencing

Question 37

Why can’t the other copy of the gene compensate in the case of uniparental diploidy?

Answer 37

The same gene on the other chromosome can not compensate for the deletion because it has been turned off by methylation, an epigenetic modification.