Question

You are studying the genetic basis of the difference in the color of two species of flowers - one that has | red flowers and one that has white. You have determined that this difference is due to a single gene and red (R) is completely dominant to white) minant to white (C). You have also identified a candidate gene (R-locus) that, while there are no differences in the coding region between red and white flowers, the locus shows a very large difference in its expression between the red and white flowers. Figure 1A depicts relative expression for the R locus in red and white flowers. Figure 13 and 1C depict read counts from RNAseq in the heterozygotes. Points above 0.5 indicate a majority of reads came from the red allele (R), points below 0.5 indicate the majority of reads came from the white allele(). Figure 1A. Normalized Expression at the R locus 1.0 0.8 0.6 Normalized Expression 0.4 0.2 RA Figure 1B. RNA seq Read Counts at R locus in heterozygotes Figure 1C. RNAseq Read Counts at R locus in heterozygotes 0.8 0.6 Proportion of total reads from the R allele 0.4 02 0. 0 8 10 0 2 4 6 8 Individuals Individuals (A). (6 pts) The heterozygous flowers (Rr) have intermediate levels of expression, yet are phenotypically wild type (Figure 1A). How can you explain this? (B) (10 pts) Referring to figures 18 and 1C, which of these figures indicates that the difference in expression between alleles is due to cis-regulation? Which indicates trans-regulation is responsible? Explain your reasoning.

Answer 1

A)

The expression of these individuals is Wild-Type is because of Haposufficiency. Haplosufficieny is a phenomenon where expression of a gene from one locus is sufficient for wild-type expression. Most genes are haplosufficient, that is, proteins produced from the transcription of one locus are enough in concentration to carry out cellular function without errors.

B)

Figure 1C indicates differences in expression due to trans-regulation while Figure 1B indicates differences in expression due to cis-regulation.

In Figure 1C, all individuals have RNAseq Read count proportions near 0.5, indicating that about 50% of transcripts originate from the R allele, while 50% of transcripts originate from the r allele. As these individuals are heterozygous at the R locus, expression of both alleles around 50% indicates that the 'r' allele influences expression from the 'R' allele, which indicates trans-regulation.

In Figure 1B, all individuals have ~90% expression from the R locus. This means that the 'R' allele is regulated independently of the 'r' allele, and regulation is cis.