Meiosis I: Homologous chromosomes separate | Meiosis II: Sister chromatids separate

Trisomy: Presence of an extra chromosome (2n+1) | Monosomy: Absence of one chromosome (2n-1)

1. Homologous chromosomes pair up. 2. Exchange of genetic material occurs during prophase I. 3. New combinations of alleles are created on the same chromosome.

1. Homologous chromosome pairs align randomly at the metaphase plate during metaphase I and II. 2. Maternal and paternal chromosomes are distributed randomly into daughter cells. 3. Different combinations of chromosomes result in the gametes.

1. Nondisjunction occurs during meiosis, resulting in an egg or sperm with an extra copy of chromosome 21. 2. The gamete with the extra chromosome 21 fertilizes a normal gamete. 3. The resulting zygote has three copies of chromosome 21 (trisomy 21), leading to Down syndrome.

Cell division that produces four genetically unique haploid daughter cells from one diploid cell; reduces chromosome number by half.

Exchange of genetic material between homologous chromosomes during prophase I of meiosis.

Random alignment and separation of homologous chromosomes during metaphase I and II of meiosis, leading to different combinations of chromosomes in gametes.

The random union of any sperm with any egg during fertilization, increasing genetic variation.

Failure of chromosomes to separate correctly during meiosis, resulting in gametes with an abnormal number of chromosomes.

Having an extra copy of a chromosome (n+1).

Missing a copy of a chromosome (n-1).