Your question is not clear, but if you see a genotype BbNN, you assume that it means that there are 4 chromosomes, or 2 homologous pairs. One pair is heterozygous for the B gene, and the other is homozygous for the N gene.
The genotype AABbCCdd indicates 4 homologus pairs of chromosomes. Those with the A, C, and D genes are homozygous for those genes, and the B gene is heterozygous.
Comments
Your question is not clear, but if you see a genotype BbNN, you assume that it means that there are 4 chromosomes, or 2 homologous pairs. One pair is heterozygous for the B gene, and the other is homozygous for the N gene.
The genotype AABbCCdd indicates 4 homologus pairs of chromosomes. Those with the A, C, and D genes are homozygous for those genes, and the B gene is heterozygous.
I hope this is what you're asking about.