There are 46 human chromosomes. These come in 23 homologous pairs. 44 (22 pairs) of these are autosomal chromosomes, whereas 2 (1 pair) are sex chromosomes. This pair of sex chromosomes determines the sex of the human baby.
Pedigrees give a tree of a family's genetic history. Circles denote females, squares denote males. A line joining shapes means marriage, whereas a branch down from the shapes means the children produced from that marriage. Pedigrees are used to identify genetic disorders, so the affected individuals are usually shaded in.
Genetic disorders are diseases passed down from parent to child through DNA. Genetic disorders can be carried on recessive alleles, dominant alleles, be sex-linked, or be related to chromosomal number. Sex-linked alleles are carried on sex chromosomes only. Chromosomal number disorders are when the individual is missing or has extra chromosomes due to the errors in the parents gametes produced through meiosis.
Genetic engineering attempts to make products useful to humans by changing the DNA of organisms such as plants and bacteria. Some techniques used in genetic engineering are extraction, restriction enzymes, gel electrophoresis, and polymerase chain reaction.
Transformation is when a cell picks up DNA from its environment and incorporates it into its own DNA. This can be forced onto the cell for genetic engineering purposes. To transform a bacterial cell, the engineered DNA is inserted into a plasmid for transformation. To transform a plant cell, the DNA is inserted into a virus which infects the DNA into the plant cell's nucleus. To transform an animal cell, the engineered DNA is injected directly into the nucleus of the egg.