An alteration to chromosome structure which only involves one chromosome is called MONOSOMY.
Alterations in chromosomes structures usually leads to mutation. Monosomy refers to the condition of heaving a diploid chromosome complement in which one chromosome lacks its homologous partner.
The graph shows the ages of the women who have breast cancer, which range from ages 40 to 50. So it shows that this type of disease is most commonly diagnosed in women of these ages. Apparently, women are more prone to getting breast cancer the older they are. This is because as you get older, you lose some of your strength to fight these carcinomas so the risk of mutation grows higher as well.
Hope this helps!
All what the word tetravalent means is that carbon can form 4 chemical bonds, due to the fact that carbon has 4 unpaired valence electrons in its furthest shell, which can be used to bond to other atoms, to form linear and cyclic structures in organic compounds.
Tetravalent also tells us indirectly what the molecular geometry of the atom would be if bonded to those number of bonds, if 4, then it would be tetrahedral and have bond angles of 109.5.
