Chromosomes carry the Genes that Mendel studied. Cytology and the chromosomal theory of inheritance

Mendel's 2nd law vs chromosome theory How to resolve it: Fruit flies and linkage (experiments by Thomas Hunt Morgan, with Drosophila melanogaster

–> Genetic linkage and Homologous recombination (caused by Chromosomal crossover, which occurs during Meiosis)

Mode of inheritance

–> Genetic dominance (gives rise to modes of inheritance)

• Diploid cells have two copies of each chromosome, called Homologous pairs, except, maybe for Sex chromosomes. These "copies" are not identical, the are homologous, they have the same genes (or almost), but just different alleles.
• Haploid. Just one copy of each chromosome. Gametes are haploid.

https://www.wikiwand.com/en/Boveri%E2%80%93Sutton_chromosome_theory