Question

Nondisjunction at meiosis can result in _____________ a. base-pair substitutions b. aneuploidy c. crossing over d. pleiotropy

Short answer

Nondisjunction at meiosis results in aneuploidy (b).

Step-by-step solution

Understanding Nondisjunction

Nondisjunction occurs when homologous chromosomes or sister chromatids fail to separate properly during meiosis, leading to gametes with an abnormal number of chromosomes.

Defining Aneuploidy

Aneuploidy refers to the presence of an abnormal number of chromosomes in a cell, such as having one extra or one missing chromosome, which can result from nondisjunction.

Examine Each Option

a. Base-pair substitutions involve changes at the DNA level, not related to chromosome segregation. b. Aneuploidy directly results from nondisjunction due to the incorrect number of chromosomes. c. Crossing over is a process during meiosis that involves exchanging genetic material, not an outcome of nondisjunction. d. Pleiotropy refers to a single gene impacting multiple traits, unrelated to nondisjunction.

Choose the Correct Answer

Based on the definitions and processes, aneuploidy (b) is the correct result of nondisjunction during meiosis.

Key concepts

Aneuploidy

Aneuploidy is a condition where cells have an abnormal number of chromosomes. Typically, humans have 46 chromosomes, which are distributed equally as 23 pairs. Aneuploidy occurs when this balance is disrupted, leading to cells with either extra or missing chromosomes.

The most common form of aneuploidy is trisomy, which means having an extra chromosome. Down syndrome is a well-known example, where individuals have an extra chromosome 21. Another example is monosomy, where there is a missing chromosome, such as Turner syndrome, where females have only one X chromosome instead of two.

Aneuploidy can have significant effects on an individual, including developmental and growth issues. It is mainly caused by errors occurring during meiosis, specifically when chromosomes fail to separate properly. Understanding aneuploidy helps us comprehend the effects of chromosomal abnormalities on human health.

Chromosomal Abnormalities

Chromosomal abnormalities refer to changes in the number or structure of chromosomes within a cell. These abnormalities can occur during cell division, specifically during meiosis. When chromosomes are not distributed properly, it can lead to either missing or extra chromosomes, contributing to various disorders.

There are two main types of chromosomal abnormalities:

• Numerical abnormalities - involve a change in chromosome number, such as aneuploidy. For instance, trisomy and monosomy are numerical chromosomal abnormalities resulting from nondisjunction.


• Structural abnormalities - involve the alteration of chromosome structure, such as deletions, duplications, inversions, or translocations of chromosome segments. These can disrupt genetic information, leading to various health issues.

Chromosomal abnormalities can cause significant effects, leading to physical and developmental challenges. They are often detected through genetic testing methods such as karyotyping, which visualizes an individual's complete set of chromosomes.

Genetic Disorders

Genetic disorders refer to diseases or conditions caused by abnormalities in an individual's DNA. These can arise from chromosomal abnormalities like aneuploidy or from mutations at specific gene locations. Genetic disorders can be inherited from parents or can occur due to new mutations during the formation of gametes.

Common genetic disorders resulting from aneuploidy include Down syndrome, Edward syndrome, and Patau syndrome. These are caused by the presence of extra chromosomes and result in varying degrees of disability and health problems.

Some genetic disorders derive from specific gene mutations rather than entire chromosomal abnormalities. Cystic fibrosis and sickle cell anemia are examples of disorders caused by mutations within a single gene. Genetic testing and counseling can help diagnose and manage these disorders, providing essential information for prospective parents and individuals at risk.

Meiosis Errors

Meiosis is a special type of cell division responsible for producing gametes, such as sperm and eggs, with half the number of chromosomes compared to somatic cells. Errors in meiosis can lead to significant biological consequences, primarily resulting in chromosomal abnormalities such as aneuploidy.

There are two main types of errors in meiosis:

• Nondisjunction - Occurs when homologous chromosomes or sister chromatids fail to separate properly during meiosis I or meiosis II. This results in gametes that contain an incorrect number of chromosomes, leading to conditions like Down syndrome.


• Errors during crossing over - Although crossing over is a natural and essential part of meiosis, where genetic material is exchanged between homologous chromosomes, mistakes can occur. These mistakes might lead to structural abnormalities in chromosomes.

Understanding meiosis errors is crucial for comprehending how genetic disorders arise and the impact they have on human health. These insights are vital for developing diagnostic and therapeutic approaches for managing genetic disorders.