Final answer:
The offspring of an RRtt x RRtt cross will all have red fur due to the dominance of the R allele and straight fur due to both parents only contributing recessive t alleles. Hence, all offspring will exhibit red, straight fur.
Step-by-step explanation:
When predicting the genetic outcomes for offspring, we can use the principles of Mendelian genetics. In this case, we are crossing two individuals both with the genotype RRtt. This means that each parent can only pass on an R allele for fur color since they are homozygous dominant (RR), and a t allele for fur texture since they are homozygous recessive (tt).
Since all offspring will receive an R allele from both parents, all offspring will have red fur. Fur color in this scenario shows complete dominance, meaning that the presence of the dominant R allele completely masks the expression of the recessive allele if it were present. However, there is no such mask here, as there is no recessive allele to be masked. Additionally, since all offspring will also receive a t allele from each parent for fur texture, they will have straight fur. Fur texture also follows a Mendelian pattern of dominance where the T allele would be dominant over the t allele, but there are no T alleles in this cross.
Thus, the offspring of an RRtt x RRtt cross will all have red, straight fur, which corresponds to option C: All offspring have red, straight fur.