Genes 2

Question 1

Meaning of Codominance? Give example with regards to blood types

Answer 1

both alleles contribute to phenotype
e.g. ABO blood type system
IA and IB dominant, Io recessive
A -> IA/IA or IA/Io
B -> IB/IB or IB/Io
AB -> IA/IB
O -> Io/Io

Question 2

Describe glycosyltransferase function for each gene

Answer 2

IA -> adds N-acetylgalactosamine (to rbc)
IB -> adds galactose
Io -> inactive (has a frameshift mutation)

Question 3

Possible molecular explanations for dominant mutations?

Answer 3

• Protein normally expressed at a critical moment
  during development is expressed constitutively
  (constantly) in the mutant
• Consider a structural protein; insufficient may be made
  if only one gene copy is active
• Consider a multimeric protein; mutant polypeptide
  may ‘poison’ the assembly

Question 4

What is epistasis? Describe some effects

Answer 4

Gene interactions (not alleles) that affect the phenotype

• 2 or more loci interacting to create new phenotypes
• Allele at one locus masks the the effects of alles at one or more other loci
• Same as above, but modifies effects instead of masks them

Question 5

What is meant by penetrance and expression?

Incomplete penetrance?

Answer 5

Penetrance and expression

Identical genes produce different expression patterns
This can be explained by the fact that the expression of
individual genes is influenced by other genes in the genome
of that particular individual, i.e. the genetic background, and
by its interactions with the environment

Incomplete penetrance

When the presence of a particular allele results in a defined phenotype in some but not all individuals.
If, for instance only 85% of people having the same
genotype show a phenotype the penetrance if 85%