Every species has a unique number of chromosomes housed within their cells. All humans have 46 chromosomes within their somatic, or body, cells. This is referred to as the diploid number of chromosomes. During meiosis, this number is reduced to 23 chromosomes per gamete (sex cell). This is known as the haploid number of chromosomes. This reduction of chromosomes is required to assure that, upon fertilization of sperm and egg, the diploid number is maintained...
Every species has a unique number of chromosomes housed within their cells. All humans have 46 chromosomes within their somatic, or body, cells. This is referred to as the diploid number of chromosomes. During meiosis, this number is reduced to 23 chromosomes per gamete (sex cell). This is known as the haploid number of chromosomes. This reduction of chromosomes is required to assure that, upon fertilization of sperm and egg, the diploid number is maintained from generation to generation.
Nondisjunction occurs when gametes are formed during meiosis. Thus, nondisjunction can effect either sperm or egg. Nondisjunction occurs when at least on pair of sister chromatids or homologous chromosomes fail to divide normally during meiosis. Nondisjunciton may occur during either meiosis I or meiosis II. This causes the gametes to have either more or less chromosomes.
Fertilization that involves gametes with the incorrect number of chromosomes as a result of nondisjunction may result in monosomy or trisomy. Monosomy is a condition in which only one chromosome of a pair is present. Trisomy is a condition in which there are three copies for a chromosome type. The syndrome/disorder that results from fertilization involving gametes produced by nondisjunction depends on the chromosome number that is affected.
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