Lecture 25: Molecular Basis to Mendelian Inheritance

Question 1

Describe the mutation which leads to wrinkled (rather than round) seeds in pea plants.

Answer 1

• In the mutant allele, a transposon is inserted into the open reading frame, disrupting both transcription (larger transcript) and translation in mutant lines.
• The gene that is mutated encodes starch branching enzyme I.

Question 2

Describe the mutation which leads to dwarf (rather than tall) pea plants.

Answer 2

• A single nucleotide substitution in the coding sequence leads to an alanine (A) to threonine (T) substitution at position 229 that reduces the activity of the enzyme.
• The gene that is mutated encodes gibberellic acid 3-oxidase.

Question 3

Describe the mutation which leads to green (rather than yellow) seeds in pea plants.

Answer 3

• In the mutant allele, a six nucleotide insertion in the coding sequence leads to a two amino acid insertion in the translated protein, disrupting gene function.
• The gene that is mutated encodes a stay green protein.

Question 4

Describe the mutations which affect seed coat and flower colour in pea plants.

Answer 4

• In the most common mutant allele, a single nucleotide change at an intron junction disrupts RNA processing leading to a transcript with an additional eight nucleotides and a truncated protein.
• The gene that is mutated encodes a basic helix-loop-helix transcription factor.