Chromosomes are thread-like structures located within the nucleus of animal and plant cells.
Chromosomes are highly condensed rods of deoxyribonucleic acid (DNA), the genetic material that contains the building blocks of life. DNA stores important information about the structure of an animal or plant and helps direct the organism as it grows and manages daily tasks. Chromosomes serve as storage for this important material, periodically dividing along with cells and replicating to make copies of the DNA they contain. Chromosomes are also very important in sexual reproduction as they allow an organism to pass genetic material on to its offspring.
Eggs and sperm are sexual reproduction cells, or gametes, found in humans.
In organisms with cell nuclei, known as eukaryotes, chromosomes are found inside the nucleus. Most of these organisms have a set of chromosomes that come in pairs. In structural cells, each cell retains a complete set of chromosomes, in the so-called diploid form, referring to the fact that the chromosome set is complete. In cells for sexual reproduction, such as eggs or sperm, each cell has only half of the genetic material of the parental organism, stored in haploid form, ensuring that the parent passes on half of its genes.
Chromosomes store the deoxyribonucleic acid (DNA) that makes up a person’s genetic code.
Each end of a chromosome is covered by a telomere, a repetitive strand of DNA that protects the chromosome from damage. Scientists sometimes look to telomeres for important information about an organism, as they appear to change over time and may be associated with aging. When chromosomes divide to make copies, the telomere also ensures that all important genetic material is copied.
Chromosomes are most easily seen during mitosis.
Each time a cell divides, the inner chromosomes are replicated. In mitosis, normal cell division, the chromosomes make copies of themselves which then pair up, so that at the end of the cell division process, two cells emerge with one set of diploid chromosomes each. When cells divide to create reproductive material, a process called meiosis, each division produces four cells, each with a haploid set of chromosomes. These cells are known as gametes, and when they meet, they contain enough genetic material to create an entirely new organism.
An individual born with an extra chromosome can function normally.
In humans, the normal number of chromosomes is 46, appearing in 23 pairs. Each pair of chromosomes stores different information and any damage to a chromosome can cause serious problems for the parent organism. Mistakes often occur during cell division, creating gaps in the genetic material of the chromosome. In some cases, an abnormal number of chromosomes appears, in a condition known as aneuploidy. Aneuploidy in reproductive cells can be a big problem as it can cause birth defects.