A stroke occurs when blood flow to a part of the brain stops. A stroke is sometimes called a brain attack.. If blood flow is cut off for longer than a few seconds, the brain cannot get nutrients and oxygen. Brain cells can die, causing lasting damage.
A cell is said to be homozygous for a particular gene when identical alleles of the gene are present on both homologous chromosomes. The cell or organism in question is called a homozygote. True breeding organisms are always homozygous for the traits that are to be held constant.
An organism is said to be homozygous for a trait when both the alleles of a gene pair are the same. lt can be homozygous dominant (TT) or homozygous recessive (It). When the two alleles in a gene pair are not the same, for example, when the genotype is Tt, the organism is heterozygous, or hybrid for that trait.