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.
These terms describe whether the two alleles (versions) of a gene carried by an organism such as a fly are the same or different. 1  Homozygous means that the organism has two of the same allele. For example: a b b fly would be homozygous. 2  Heterozygous means that the organism has two different alleles.