In Drosophila, the genes r and s are linked. Flies of genotype r s/r s and rs /rs are crossed and an F1 obtained. The F1 allele arrangement is called:

repulsion (trans)

Explanation:

Repulsion refers to the phenomenon by which each homologous chromosome contains one dominant and one recessive allele from two different linked genes. A trans arrangement occurs when an individual is heterozygous for two linked genes, where the recessive allele for one particular gene is located on the same chromosome as the dominant allele for the other linked gene, thereby dominant and recessive alleles are said to be “in repulsion”. Conversely, a cis arrangement occurs when both dominant alleles are located on one chromosome and both recessive alleles on the other.

primary succession begins with a bare rock and ends with a forest secondary succession begins after a natural disaster where there is a temporary setback after a forest fire or local destruction, but the surrounding area can fill in

the areas around the equator