Sketch a cell with three pairs of chromosomes undergoing meiosis, and show how non-disjunction can result in the production of gametes with extra or missing chromosomes.

Verified step by step guidance

1. Start by sketching a cell with three pairs of homologous chromosomes (a total of six chromosomes). Label each pair with different colors or patterns to distinguish them (e.g., Pair 1: red, Pair 2: blue, Pair 3: green). Place the chromosomes in the nucleus of the cell in their duplicated form (sister chromatids).
2. Illustrate the stages of meiosis I. During prophase I, show homologous chromosomes pairing up (synapsis) and crossing over. In metaphase I, align the homologous pairs along the metaphase plate. In anaphase I, depict the separation of homologous chromosomes to opposite poles. In telophase I, show the formation of two haploid cells, each with three duplicated chromosomes.
3. Illustrate the stages of meiosis II. In prophase II, show the chromosomes in each haploid cell preparing for division. In metaphase II, align the chromosomes along the metaphase plate. In anaphase II, depict the separation of sister chromatids to opposite poles. In telophase II, show the formation of four haploid gametes, each with three single chromosomes.
4. To demonstrate nondisjunction, modify the anaphase stage in either meiosis I or meiosis II. For meiosis I nondisjunction, show one homologous pair failing to separate, resulting in one cell with an extra chromosome and one cell missing a chromosome. For meiosis II nondisjunction, show one pair of sister chromatids failing to separate, resulting in one gamete with an extra chromosome, one gamete missing a chromosome, and two normal gametes.
5. Conclude by labeling the resulting gametes to indicate their chromosomal composition. Highlight how nondisjunction can lead to conditions such as trisomy (e.g., Down syndrome) or monosomy (e.g., Turner syndrome) if these gametes are involved in fertilization.

Key Concepts

Meiosis

Meiosis is a specialized type of cell division that reduces the chromosome number by half, resulting in four genetically diverse gametes. It consists of two sequential divisions: meiosis I, where homologous chromosomes are separated, and meiosis II, where sister chromatids are separated. This process is crucial for sexual reproduction, ensuring genetic variation through recombination and independent assortment.

Nondisjunction

Nondisjunction is the failure of homologous chromosomes or sister chromatids to separate properly during meiosis. This can occur in either meiosis I or meiosis II, leading to gametes with an abnormal number of chromosomes. If such gametes participate in fertilization, they can result in aneuploidy, where the resulting zygote has extra or missing chromosomes, potentially leading to genetic disorders.

Aneuploidy

Aneuploidy refers to an abnormal number of chromosomes in a cell, which can arise from nondisjunction during meiosis. Common forms of aneuploidy include trisomy, where there is an extra chromosome (e.g., Down syndrome), and monosomy, where a chromosome is missing. The presence of aneuploidy can significantly impact development and lead to various health issues, making it a critical concept in genetics.