Skip to content
📢We are still a growing community and would love some help. Want to contribute? Join us by mailing an e-mail of interest to "r6394175@gmail.com"
Start helping our community →
← Theoretical B

Q23 — ACE2/CTS1 Mutations and Multicellularity in Yeast

Theoretical B Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Extensions of Mendelian Inheritance

Sometimes a formation of multicellular, organized structures can be observed in baker’s yeast (Saccharomyces cerevisiae) in which newly divided yeast cells do not separate from the parent cell, illustrating a potential transition step from unicellular to multicellular organisms. The emergence of multicellular structures can be influenced by various factors, one of which is a mutation in the ACE2 gene, responsible for the transcriptional regulation of the protein-coding gene - CTS1. To investigate this, scientists crossed different yeast strains and sequenced ACE2 gene alleles.

Panel A: two fluorescence micrographs of chitin-stained yeast, wild-type single cells (G) vs. mutant multicellular clusters (H). Panel B: a cross grid of 6 blue/red-labeled strains showing single-celled (S) or multicellular (R) offspring. Panel C: a bar chart of relative CTS1 expression, high in wild-type and low in two mutant strains. Figure 1. A Wild type (G) and ACE2 mutant (H) yeast cells. The preparations were stained with dye for chitin. B Results of crosses between strains: blue - wild type, red - ACE2 mutants; R-multicellular, S-unicellular offspring. C Relative expression level of the CTS1 gene (black bar indicates the wild type, white and gray indicate two different strains with mutations in ACE2).

Three DNA sequencing chromatogram traces (Str 1, Str 8, and an unknown sample U) around a poly-A run, with Str 8 one adenine longer than Str 1 and the unknown showing overlapping double peaks. Figure 2. Ace2 gene region sequencing results; U - unknown.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. When subjected to identical incubation conditions, wild-type yeast cultures exhibit a faster settling rate compared to mutant yeast cultures.
B. The mutation in the yeast strain 8 causes a frameshift and is recessive.
C. The unknown sequencing sample in Figure 2 may be the offspring of a cross between strains 1 and 8.
D. The product of the CTS1 gene likely plays an important role in the final stages of cell division rather than in the initial stages.
← Previous: Q22 Next: Q24 →

Question reproduced from IBO 2024, Theoretical Exam Part B, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF