Consider the following statements. (a) All the genes, which can inherit together from one generation to another generation constitute a linkage group. (b) Genes that are linked but never cross over is known as incomplete linkage. (c) Mutual exchange of blocks of homologous genes between a pair of homologous chromosomes is known as crossing over. (d) The chromosomes in an organism that determine the sex of an individual, are called sex chromosomes. Which of the above statements is/are incorrect?