Chromosomes - Pull up Those GenesChromosomes are the things that make organisms what they are. They carry all of the information used to help a cell grow, thrive, and reproduce. Chromosomes are made up of DNA. Segments of DNA in specific patterns are called genes. Your genes make you who you are. You will find the chromosomes and genetic material in the nucleus of a cell. In prokaryotes, DNA floats in the cytoplasm in an area called the nucleoid.
Loose and TightChromosomes are not always visible. They usually sit around uncoiled and as loose strands called chromatin. When it is time for the cell to reproduce, they condense and wrap up very tightly. The tightly wound DNA is the chromosome. Chromosomes look kind of like long, limp, white hot dogs. They are usually found in pairs.
Completing the SetsScientists count individual strands of chromosomes. They count individuals not every organism has pairs. You probably have 46 chromosomes (23 pairs). Peas only have 12. A dog has 78. The number of chromosomes is NOT related to the intelligence or complexity of the creature. There is a crayfish with 200 chromosomes. Does that make a crayfish five times smarter or more complex than you are? No. There are even organisms of the same species with different numbers of chromosomes. You will often find plants of the same species with multiple sets of chromosomes.
Chromosomes work with other nucleic acids in the cell to build proteins and help in cell division. You will most likely find mRNA in the nucleus with the DNA. tRNA is found outside of the nucleus in the cytosol. When the chromosomes are visible, cells with two complete sets of chromosomes are called diploids (46 in a human). Most cells are diploid. Cells with only one set (23 in a human) are called haploid cells. Haploids are most often found in cells involved in sexual reproduction such as a sperm or an egg. Haploid cells are created in cell division termed meiosis.
Chalk Talk: DNA (US-NSF Video)