Answer:
Centromere
Step-by-step explanation:
Centromers are regions of the primary constriction of the chromosome. In this place, the kinetochore is located, a structure formed by proteins that guarantee the connection of sister chromatids (X-shaped chromosomes) in the mitotic spindle. The centromere allows the chromosome to be divided into arms, which may have different sizes depending on the position of the centromere. When we observe an unduplicated chromosome, it is possible to notice the presence of a centromere and two arms. From this we can conclude that the X-shaped chromosomes are linked through the centromere.