Genetics and Health Week 7

Question 1

Define each of the following

A) Sex-Linked Traits
B) Sex-Limited Traits
C) Sex-Influenced Traits

Answer 1

A) Sex-Linked Traits: Caused by mutations in genes on the sex chromosomes (X/Y)

B) Sex-Limited Traits: Phenotype only observed in one sex and not the other

C) Sex-Influenced Traits: Alleles are dominant in one sex and recessive in the other

Question 2

Colour Vision Deficiency

Type of Disorder
Mutations

Answer 2

 X-linked Recessive
 Males are affected more than females
 OPN1LW (yellow/orange detection)
 OPN1MW (yellow/green detection

Question 3

Hypophosphatemic Rickets

Type of Disorder
Mutation in which gene
Functions (Low levels of)
Result

Answer 3

 X-linked Dominant
 Mutations in the PHEX gene (role of this protein is Vitamin D synthesis or phosphate metabolism)
 Low levels of phosphate in the blood (hypophosphatemia)
 Lower amount of calcium which leads to weaker and softer bones
 It affects mostly females than males because women have two times the risk as they have two X chromosomes, they inherit the X-chromosome from the mother and father

Question 4

Duchenne Muscular Dystrophy (DMD)

Type of Disorder
Mutation
Functions
Result

Answer 4

• Genetic conditions characterized by progressive muscle weakness and wasting (atrophy)
• Weakness in the pelvic region
• Primarly affects skeletal muscles and their movement
• Those with this disorder learn to stand and walk late and their speech development is slow
• Hypertrophy of the calf muscles is a classic sign
• Pseudohypertrophy is not a true hypertrophy, accumulation of fat and connective tissue
• Boys with this disorder will use a wheelchair at age 10-12, death occurs at age 20
• Most common cause of death is cardiac muscle failure/ respiratory failure
• X-linked recessive
• Random X-inactivation (Barr bodies) in females will cause some muscle cells to lack dystrophin
• Males with DMD rarely reproduce

Question 5

Becker Muscular Dystrophy (BMD)

Answer 5

 Mild form of DMD
 Symptom onset occurs in the second decade of life, inability to walk occurring about 20 years
 Cardiac involvement does not correlate with the severity of skeletal muscle weakness
 Defect in the DMD gene that encodes dystrophin protein, it is considered the largest gene which means there is more area for stuff to go wrong
 Important structural proteins, connects proteins on sarcolemma action on Z-Disc
 Female carriers of DMD or BMD have heart problems X - linked Recessive

Question 6

Haemophilia

Answer 6

• X-linked recessive disorder
• Characterized by the inability to properly form blood clots
• Mutations in the F8 gene (responsible for making coagulation factor V111/ severe problems = Haemophilia A)
• Mutations in the F9 gene (responsible for making coagulation factor IX/ mild problems = Haemophilia B)
• Severity determined by where along the blood clotting pathway it is affected
• Originally treated with blood transfusions and infusions of a blood derived substance (anti-haemophilic factor), but this method is very expensive and there is risk of contracting serious diesases
• Recombinant clotting factors has alleviated the problem

Question 7

Kennedy Disease

Answer 7

• A progressive muscular atrophy that affects motor neurons
• Also known as spinal and bulbar muscular atrophy, affect swallowing and speech
• Mutation in the AR gene, causes expansion of CAG triplets repeats in Androgen Receptor protein)
• X-linked Recessive
• Heterozygote females are usually asymptomatic (protected by second X chromosome and random X inactivation)
• Homozygous females (have more mild phenotype, with muscle cramps and occasional tremors, low androgen levels in females

Question 8

Describe the Human Mitochondrial Genome

Answer 8

 Have a singular circular chromosome
 Inherited maternally
 Circular geonome, no histones and does not form chromatin
 Always open and exposed, more susceptible to mutation
 2-10 copies of mitochondrial DNA
 Mitochondria require many nuclear-encoded proteins to function

Question 9

In Mitochondrial Mutations and Diseases, what is the differences between blue circles and pink circles?

Answer 9

o Blue circles indicate mutations in the gene impair protein synthesis
o Pink circles indicate mutated genes that encoded respiratory chain proteins

Question 10

Define Bottleneck Affect

Answer 10

Rare alleles that dominate the mtDNA pool in cells

Question 11

What is the difference between Homoplasmy and Heteroplasmy?

Answer 11

Homoplasmy: where all copies of mitochondrial genome (mtDNA) are exactly the same

Heteroplasmy: where all copies of mitochondrial genome (mtDNA) are not the same

Question 12

Leigh Disease

Answer 12

 mtDNA mutation is the most common (encoding ATPase6 – causing deficiencies in ATP production and OXPHOS
 Most common treatment for Leigh disease is administration of thiamine (vitamin B1)
 oral sodium bicarbonate or sodium citrate may also be prescribed for management of lactic acidosis