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 individual that is homozygous recessive for a particular trait carries two copies of the allele that codes for the recessive trait. This allele, often called the recessive â¦ allele is usually represented by the lowercase form of the letter used for the corresponding dominant trait. The genotype of an organism that is homozygous recessive for a particular trait is represented by a doubling of the appropriate letter, such as pp.