Genetics - Phenotypic variability

Question 1

What are the different variations for phenotype?

Answer 1

1. Different disease, same name
2. Effect of environment
3. Same disease but affect sexes differently
4. Effects of other genes
5. Different mutations in same gene –> different phenotype
6. Unstable mutations

Question 2

What happens when there are different diseases or causal gene but the same name?

Answer 2

Has different sub-types, all result in same symptom but different disease outcomes, inheritance patterns & underlying causes

Question 3

What are the causes of sub-types of mutations?

Answer 3

Mutation in different genes

Question 4

How does the effect of the environment affect the genetic disease?

Answer 4

Natural history and prognosis

eg increase risk of patient developing cancer/cause accumulation of damage

Question 5

How are some diseases affected by the environment?

Answer 5

Not all people develop same type same time

=> Second event promote

Question 6

How can genetic diseases affect different sexes differently?

Answer 6

Physiological differences (eg presence/absence of organ: [lack of BRCA-1/2]
M - Prostate cancer
F - Ovarian cancer)

• One sex can have higher risk in inheriting and passing on the mutation

Question 7

How are some genetic diseases affected by interaction with other genes?

Answer 7

Improve or worsen the condition

-eg eye colour (must have active HERC2 gene for OCA-2 [melanin] to work)

Question 8

How can different mutations in same gene lead to different phenotypes?

Answer 8

• One vs multiple mutation in same gene

- different types of mutation [frame shift deletion, substitution etc)

Question 9

How can unstable mutation affect genetic disorders?

Answer 9

Large group of diseases termed “Trinucleotide repeat disorders”
- mutation where region of 3 repeated nucleotides in genome increases in number during DNA. replication

[>27 = stable, function normal
Above threshold = not stable]

Greater number of repeats = more severe phenotype
(Earlier onset, greater severity of symptoms in each succeeding generation - increase repeats)

Question 10

What would be the likely cause of phenotypic variation in genetically identical twins?

Answer 10

• Environmental

Question 11

What would be the likely cause of phenotypic variation in non-genetically identical individuals with same mutation? (eg family)

Answer 11

• Environmental

- Existence of variation in other gene that interact with the mutated gene

Question 12

What would be the likely cause of phenotypic variation in unrelated individuals?

Answer 12

• Different mutation/disease-causing gene

- Unstable mutation of trinucleotide repeat disease (increase severity)