WEEK 3

Question 1

What does the term “gene interaction” mean?

Answer 1

It is used to express the idea that multiple genes interact to express a certain phenotype

Question 2

What are two examples of Pleiotropy?

Answer 2

Marfan syndrome & Porphyria variegata

Question 3

Define ‘Pleiotropy’

Answer 3

The phenomenon in which a single gene mutation results in multiple phenotypical abnormalities

Question 4

Male individuals are said to be __________________

Answer 4

Hemizygotic

this is because males have XY chromosomes therefore they only require one copy of the gene

Question 5

How can you notice an X-linked recessive gene in a pedigree tree?

Answer 5

1. Skipping generation
2. Mostly affecting males
3. No male to male transmission (e.g father cannot pass on to son)
4. Sons of heterozygous mothers have a 50% chance of being affected
5. Females usually must be homozygous to be affected

Question 6

How can you notice an X-linked dominant gene in a pedigree chart?

Answer 6

1. Fathers will transmit to all daughters but no sons
2. Mothers will transmit to 50% to daughters and sons
3. No male to male transmission
4. Transmitted through both parents

Question 7

Define ‘Penetrance’

Answer 7

The percentage of individuals that show at least some degree of expression of a mutant genotype

Question 8

What is ‘expressivity’?

Answer 8

The range of expression of the mutant genotype

Question 9

What is ‘imprinting’?

Answer 9

A type of marking process that has a memory and involves DNA Metyhlation (silencing of a gene)

Question 10

What are two examples of imprinting?

Answer 10

Prader-Willi syndrome & Angelman syndrome

Question 11

What is Epistasis?

Answer 11

Where the expression of one gene masks or modifies the effect of a second gene

Question 12

What phenotypic expression can result from Epistasis?

Answer 12

When phenotypic characteristics act in an antagonistic manner, masking occurs. When genes exert their influence on another, complementary/cooperative phenotypes occur.

Question 13

What is ‘Variable expressivity’?

Answer 13

Patients with the same genotype have varying phenotypes

(e.g varying disease severity)

Question 14

Define ‘Incomplete penetrance’

Answer 14

Not all individuals with a mutant genotype show the mutant phenotype

% penetrance X probability of inheriting genotype = risk of expressing phenotype

Question 15

Define ‘genomic imprinting’

Answer 15

An analogous situation in which a segment of DNA is marked and that mark is retained and recognised throughout the life of the organism inheriting the marked DNA

Question 16

What is Prader-Willi syndrome?

Answer 16

Prader-Willi syndrome occurs when maternally derived genes are silenced and the disease occurs when the paternal allele is deleted or mutated. Chromosome 15 of parental origin is involved.

Symptoms include Hyperphagia (excessive eating), Obesity, Intellectual disability, Hypogonadism (not enough testosterone), Hypotonia (reduced muscle tone)

25% of cases are due to maternal uniparental disomy
POP: Prader-Willi, Obesity/overeating, Parental allele deleted

Question 17

What is Angelman syndrome?

Answer 17

Occurs when paternally derived UBE3A is silenced and disease occurs when the maternal allele is deleted or mutated. UBE3A on chromosome 15 of maternal origin is involved.

Symptoms include Seizures, Ataxia, severe Intellectual disability, inappropiate Laughter
(set SAIL for angel island)

5% of cases are due to paternal uniparental disomy
(MAMAS: Maternal allele deleted, Angelman syndrome, Mood, Ataxia, Seizures)