Cell Chromosomes: Structure and Function

Chromosomes

• The nucleus of a cell controls all of its activities.
• The nucleus of every cell contains structures called chromosomes.
• Chromosomes are only visible with a light microscope when a cell is dividing.
• Chromosomes need to be coloured with special stains to be seen.
• Chromosomes were discovered in the nineteenth century.
• A photograph shows a plant cell beginning to divide into two; cells are stained with a special dye that colours the chromosomes dark red.
• Fruit flies have especially thick chromosomes called giant chromosomes, which are much easier to see than most.
• Chromosomes look like a long striped thread.
• Different species of organisms have different numbers of chromosomes in the nuclei of their cells.
• Human cells have 46 chromosomes.
• Fruit fly cells have eight chromosomes.
• Mango trees have 40 chromosomes.
• Scientists assign numbers to chromosomes in a sequence, starting with the longest one.
• In human cells, chromosome 1 is the longest, followed by chromosome 2 etc.
• Somatic (body) cells in an organism have the same kind and number of chromosomes.
• Humans have 46 chromosomes in skin, heart, and muscle cells.
• Fruit flies have 8 chromosomes in skin, heart, and muscle cells.
• Humans have two of each kind of chromosome, visible in a photograph of chromosomes in a human cell.
• Individuals do not literally line up individual chromosomes by size, but they have been lined up in size order in a photograph/image.
• Before a cell divides, each chromosome makes a copy of itself.
• The two copies then stay joined together part way along their length.

Genes

• Each chromosome is made up of hundreds of different genes.
• Genes are arranged in a particular sequence along the chromosome.
• Each gene helps to control a particular characteristic in the organism.
• On a diagram of a short chromosome, the stripes represent different genes.
• Scientists are still discovering which genes are found on which type of chromosome in humans.
• Chromosome 1 contains about 2000 different genes.
• Chromosome 15 is a much shorter chromosome and has about 600 different genes.
• Discovering exactly what each of these genes do is not easy, but research is increasing scientists' knowledge.
• Two genes on chromosome 15 help determine eye colour.
• Everyone has genes for eye colour in the same place on their chromosome 15s but there are different versions.
• One person might have a version for blue eyes, while another might have a version for brown eyes.
• Genes have different versions, one person could have a chromosome 15 with eye colour genes that give them blue eyes while another may have brown eyes.
• Different versions of genes result in two sisters having different eye colours.

DNA

• Chromosomes are made of a chemical substance called DNA.
• Each chromosome is one enormously long molecule of DNA.
• This means that genes are also made of DNA.
• A DNA molecule has a shape like a twisted ladder, called a double helix.
• One gene could be a length of DNA with about 2500 of these twists.
• Because DNA molecules are much too small to see, the twists are not visible when viewed under a microscope.
• DNA was first discovered in the 1950s.
• Scientists have discovered how the DNA in genes helps determine human and other organism characteristics.
• The DNA in a cell determines what the cell does and instructions to make a functioning cell and a whole organism.
• A gene is a unit of heredity transferred from parent to offspring that determines some characteristics of the offspring.
• A chromosome is a structure inside the nucleus of a cell; it is made of proteins and DNA organized into genes.
• Each human cell normally contains 23 pairs of chromosomes.
• Chromosomes are threadlike structures, made of protein and a single molecule of DNA, which serves to carry the genomic information from cell to cell.
• DNA is a self-replicating material present in living organisms as the main constituent of chromosomes and carries genetic information.
• The chemical basis of inheritance is DNA.
• DNA is usually found in the nucleus of a cell, in the chromosomes.
• A small section of DNA that determines a particular feature is called a gene.
• Genes determine features by instructing cells to produce particular proteins, which leads to developing a specific feature.
• A gene is a section of DNA that codes for a particular protein.
• DNA can replicate and make an exact copy of itself.
• When a cell divides by mitosis, each new cell receives the same amount of DNA, making the cells genetically identical.

Explore the structure and function of chromosomes within cells. Chromosomes, found in the nucleus, become visible during cell division when stained. Different species have varying chromosome numbers; for example, human cells have 46 chromosomes.