Question

Nondisjunction that leads to problems in offspring can occur in: a. mitosis b. meiosis I only c. meiosis I and II d. mitosis, meiosis I, and meiosis II

Short answer

Nondisjunction that leads to problems in offspring can occur in meiosis I and II. Therefore, the correct answer is c. meiosis I and II.

Step-by-step solution

Understand the terms

First, let's understand the terms: 1. Nondisjunction: Nondisjunction is an error in cell division that occurs when chromosomes do not separate properly, resulting in gametes with an incorrect number of chromosomes. 2. Mitosis: Mitosis is a process of cell division that results in two daughter cells, each with the same number of chromosomes as the parent cell. 3. Meiosis: Meiosis is a type of cell division that produces gametes (sperm and egg cells) with half the number of chromosomes as the parent cell. It includes two stages, meiosis I and meiosis II.

Determine where nondisjunction can occur

Next, let's determine where nondisjunction can occur in each cell division process. 1. Mitosis: As mitosis produces two daughter cells with the same number of chromosomes, a nondisjunction event in mitosis would not lead to problems in offspring. It could, however, result in problems for the cell itself. 2. Meiosis I: Nondisjunction can occur during meiosis I if homologous chromosomes do not separate properly. This would lead to gametes with too many or too few chromosomes, which could result in problems in offspring if fertilization occurs. 3. Meiosis II: Nondisjunction can also occur during meiosis II if sister chromatids do not separate properly. Similar to meiosis I, this would lead to gametes with an incorrect number of chromosomes, potentially causing problems in offspring.

Choose the correct answer

Now, let's choose the correct answer based on our analysis. Nondisjunction events that could lead to problems in offspring occur in: a. mitosis b. meiosis I only c. meiosis I and II d. mitosis, meiosis I, and meiosis II Since we determined that nondisjunction events that cause problems in offspring can only occur during meiosis I and meiosis II, the correct answer is: c. meiosis I and II

Key concepts

Mitosis

Mitosis is a fundamental process for life, where a single cell divides to produce two identical daughter cells, preserving the chromosome number. This type of cell division is essential for growth, repair, and asexual reproduction in single-celled organisms. During mitosis, the cell goes through phases such as prophase, metaphase, anaphase, and telophase.

In prophase, chromosomes condense and the nuclear envelope breaks down. In metaphase, chromosomes align at the equatorial plate, and during anaphase, they are pulled apart to opposite poles of the cell. Finally, in telophase, the cell splits through cytokinesis, resulting in two genetically identical cells. Mitosis maintains genetic stability by ensuring each daughter cell receives an exact copy of the parent's chromosomes. However, errors like nondisjunction can occur, but typically they do not result in problems for offspring since mitosis is not involved in the production of gametes.

Meiosis

Meiosis, on the other hand, is a specialized form of cell division that reduces the chromosome number by half, producing four genetically diverse gametes. This process is vital for sexual reproduction and biological diversity. Meiosis consists of two sequential stages: meiosis I and meiosis II.

Meiosis I

In meiosis I, homologous chromosomes—each consisting of two sister chromatids—pair up and can exchange genetic material in a process called crossing over, which occurs during prophase I. After aligning at the metaphase plate in metaphase I, the homologous chromosomes, rather than the sister chromatids, are separated during anaphase I. This stage ends with two cells, each with half the original chromosome count but still comprising sister chromatids.

Meiosis II

Meiosis II resembles mitosis, but here, each of the two cells from meiosis I divides again without replicating their DNA, leading to four haploid cells. In anaphase II, the sister chromatids finally separate, resulting in gametes. Nondisjunction in either meiosis I or II can result in gametes with an abnormal chromosome number, potentially leading to disorders such as Down syndrome when such gametes are involved in fertilization.

Chromosomes

Chromosomes are the carriers of genetic material within cells, composed of DNA and proteins. Humans typically have 46 chromosomes in each body cell, arranged in 23 pairs, with one member of each pair contributed by each parent.

Chromosomes play a crucial role in heredity and genetic diversity, particularly through the processes of mitosis and meiosis. It's essential that during cell division, chromosomes are accurately replicated and evenly distributed to the daughter cells to prevent genetic disorders. Errors in chromosome separation, or nondisjunction, can lead to cells with extra or missing chromosomes, known as aneuploidy. This can have mild to severe consequences for the organism, depending on which chromosomes are affected and whether the nondisjunction occurred during meiosis, potentially affecting offspring, or mitosis, typically affecting only the individual cell.