Genetics Lecture 3

Question 1

What is the defining symptom of alkaptonuria?

Answer 1

Urine turns black on exposure to air.

Question 2

Is alkaptonuria genetic or acquired?

Answer 2

Is genetic.

Question 3

What is the cause of albinism?

Answer 3

Inability to convert tyrosine to DOPA, a precursor to melanin.

Question 4

What is the cause of phenylketonuria?

Answer 4

Inability to convert phenylalanine to tyrosine.

Question 5

Define prototroph strain of neurospora.

Answer 5

Wild type neurospora able to grow on minimal media.

Question 6

Define auxotroph strain of neurospora.

Answer 6

Mutant strain that cant live on minimal media.

Question 7

How can the amino acid needed for auxotroph growth be isolated?

Answer 7

Grow on minimal media supplemented with one amino acid at a time.

Question 8

Genetic diseases often involve disruption of a chain reaction. How can it be known which step of the reaction is affected?

Answer 8

Grow on minimal media supplemented sequentially with reaction substrates.

Question 9

What is the incidence of phenylketonuria?

Answer 9

1/12,000

Question 10

Mutation to what enzyme causes phenylketonuria?

Answer 10

Phenylalanine hydroxylase.

Question 11

What happens to phenylalanine in the body of an individual with phenylketonuria?

Answer 11

Accumulates, and is converted to phenylpyruvic acid.

Question 12

Define the pleiotropic effect using phenylketonuria as an example.

Answer 12

When a gene influences more than one seemingly unrelated phenotypic effects. phenylketonuric individuals will have no thyroxine, adrenaline, or melanin.

Question 13

Can phenylketonuria be cured or managed?

Answer 13

No cure, perhaps in gene therapy.

Can be managed with diet restrictions.

Question 14

Is lesh-nyham syndrome a dominant or recessive gene? Is it a fatal gene?

Answer 14

Is a fatal recessive gene.

Question 15

What is the incidence of lesh-nyham syndrome?

Answer 15

1/10,000

Question 16

Lesh-nyham syndrome is caused by a deficiency of which enzyme? What is a conseqeunce of this?

Answer 16

Phyoxanthine-guanine phosphoribosyl transferase.

Causes pruines to accumulate, and converted to uric acid.

Question 17

What are the main symptoms of lesh-nyham syndrome?

Answer 17

Severe neurological symptoms, including paralysis.

Question 18

What is the incidence and rarity of tay-sachs disease like in different populations?

Answer 18

Rare in the general population, but high in the Ashkenazi Jews, with an incidence of 1/3,600.

Question 19

Tay-sachs disease is caused by a deficiency in that gene? What does it encode for? What does it do?

Answer 19

Defect in HexA coding for the lysozomal enzyme N-acetylhexosaminidase A.
Cleaves group from brain ganglioside Gm2, which accumulates in tay-sachs disease individual.

Question 20

What are the symptoms of tay-sachs disease? What is the prognosis at birth?

Answer 20

Reaction to sharp sounds, and a cherry-coloured spot on their retina.
Prognosis is 1 year afterbirth.

Question 21

Is sickle-cell disease dominant or recessive? Is it lethal?

Answer 21

Recessive, and non-lethal.

Question 22

What is sickle-cell disease a mutation to?

Answer 22

Haemoglobin, B subunit.

Question 23

What haemoglobin composition do heterozygous individuals of sickle-cell disease have?

Answer 23

Half normal, half sickle celeld.

Question 24

What amino acid change is sickle-cell disease caused by, and how does this change induce the disease?

Answer 24

Point mutation changing Glu to Val, which is hydrophobic. This creates a hydrophobic patch on the complete haemoglobin, causing them to clump together and precipitate, warping the cell, and causing loss of oxygen capacity.

Question 25

What is the most common lethal disease amongst Caucasians?

Answer 25

Cystic fibrosis.

Question 26

What is the incidence of cystic fibrosis in newborns, and carriers?

Answer 26

1/2,000 newborns

1/23 are carriers.

Question 27

What are 5 symptoms of cystic fibrosis?

Answer 27

Pulmonary, pancreatic, and digestive dysfunction.

High viscosity mucus accumulates in the lung, leading to secondary infection.

Question 28

Dysfunction of what protein causes cystic fibrosis? What is it normally?

Answer 28

The cystic fibrosis transmembrane conductance receptor - CFTR, a chlorine channel.

Question 29

What kind of mutation causes cystic fibrosis?

Answer 29

Deletion of 3 base pairs - one missing amino acid.