Complexities of Inheritance

Question 1

The Complementation Test

Answer 1

The functional definition of a gene
- 2 diff recessive mutations are considered alleles of different genes if a cross between homozygous recessives result in non-mutant progeny i.e. complement each other

Question 2

The Complementation Test

Answer 2

If 2 genes are required to produce a phenotype + one of

• No functional copy of one gene = mutant phenotype if both parent have diff mutation in same gene
• Wild type phenotype observed if offspring gets 1 functional copy of both genes

Question 3

Epistasis

Answer 3

Interaction between genes causes change in Mendelian ratios
- 1 gene can interfere with or mask the phenotypic expression of another gene leading to novel phenotype
- Multiple genes involved

Question 4

Incomplete penetrance

Answer 4

Not all individuals with mutant gene will develop associated phenotype

Question 5

Variable expressivity

Answer 5

Different individuals will show the phenotype more strongly than others

Question 6

Incomplete dominance

Answer 6

Phenotype of the heterozygous is intermediate between the phenotype of homozygous genotypes

e.g. II = red petals + ii = ivory
Ii = pink

Question 7

Codominance

Answer 7

The heterozygote expresses traits of both alleles
- Capitals are used for both alleles as there’s no dominant/recessive relationship

e.g. blood type - A and B are codominant