chromosomes in nucleus carry genes that contain instructions for making both new cells and all tissues and organs needed to make entire new you
a gene is small packet of info that controls a characteristic of your body, it is a section of DNA, the unique molecule that makes up your chromosomes. The genes are grouped together on chromosomes. You have 46 chromosomes in nucleus of body cells and are arranged in 23 pairs- in each pair 1 chromosome inherited from father, 1 from mother. Sex cells(gametes) only have 1 chromosome from each pair so only have 23 chromosomes in total
body cells divide in series of stages called cell cycle. cell division in cell cycle involves process of mitosis and produces 2 identical cells so all normal body cells have same chromosomes and so same genetic info. Cell division by mitosis produces the additional cells needed for growth and development in multicellular organisms and for replacement of worn out or damaged cells.
in asexual reproduction, cells of offspring are produced by mitosis from cells of their parent so they contain exactly same genes as their parent with little or no genetic variation.
the cell cycle is short as baby develops before born when new cells being made all the time, remains fairly rapid during childhood, and then slows down once puberty over and body is adult. however even in adults there are regions where continued growth or regular replacement of cells eg hair follicles, skin, blood, lining of digestive system
cell cycle in normal healthy cells follows regular pattern:
stage 1- longest stage, cells grow bigger, increase their mass and carry out normal cell activities. they replicate their DNA to form 2 copies of each chromosome ready for cell division and increase number of sub-cellular structures such as mitochondria, ribosomes and chloroplasts ready for cell to divide
stage2- mitosis: 1 set of chromosomes pulled to each end of dividing cell and nucleus divides
stage3- cytoplasm and cell membranes also divide to form 2 identical daughter cells
mitotic cell division is important in growth, repair, and development of multicellular organisms
in a child, mitotic cell divisions produce new cells faster than old ones die, as an adult cell death and mitosis keep more or less in balance, as you get old mitosis slows down and you show signed of aging
