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Nondisjunction in Meiosis 1 vs. Nondisjunction in Meiosis 2 — What's the Difference?

By Tayyaba Rehman & Urooj Arif — Published on February 16, 2024
Nondisjunction in Meiosis 1 occurs when homologous chromosomes fail to separate, while in Meiosis 2, it's when sister chromatids don't separate. Both lead to aneuploidy.
Nondisjunction in Meiosis 1 vs. Nondisjunction in Meiosis 2 — What's the Difference?

Difference Between Nondisjunction in Meiosis 1 and Nondisjunction in Meiosis 2


Key Differences

Nondisjunction in Meiosis 1 and Meiosis 2 are errors in chromosome segregation during the process of meiosis, resulting in gametes with an incorrect number of chromosomes. In Meiosis 1, nondisjunction occurs when homologous chromosomes fail to separate and move to opposite poles during anaphase I. This results in one gamete receiving both homologues of a chromosome and the other gamete receiving none. In contrast, nondisjunction in Meiosis 2 happens when sister chromatids fail to separate during anaphase II, leading to gametes where one contains two copies of a single chromosome and another contains no copy.
The consequences of nondisjunction in Meiosis 1 and Meiosis 2 differ because of the timing within the meiotic process. Nondisjunction in Meiosis 1 leads to all resulting gametes being affected — two gametes will have an extra chromosome (n+1) and two will have one less chromosome (n-1). However, nondisjunction in Meiosis 2 affects only half of the gametes, producing two gametes with the correct number of chromosomes (n), one gamete with an extra chromosome (n+1), and one gamete with one fewer chromosome (n-1).
The impact of nondisjunction on the offspring depends on which meiotic division it occurs in. Nondisjunction in Meiosis 1 tends to have a more widespread effect since all resulting gametes from that meiosis are abnormal. This can lead to disorders such as Down syndrome, Turner syndrome, and Klinefelter syndrome, depending on the specific chromosomes involved. In contrast, nondisjunction in Meiosis 2 may result in a subset of gametes being abnormal, potentially leading to a similar spectrum of chromosomal abnormalities but with a lower probability of occurrence.
Understanding the difference between nondisjunction in Meiosis 1 and Meiosis 2 is crucial for genetic counseling and diagnosing chromosomal abnormalities. It helps in predicting the likelihood of a disorder being passed on to offspring and in understanding the genetic makeup of individuals with chromosomal abnormalities. Both types of nondisjunction contribute significantly to the occurrence of aneuploidy in humans, impacting fertility, pregnancy viability, and the health of the offspring.
In summary, while both nondisjunction events in Meiosis 1 and Meiosis 2 lead to aneuploidy, their outcomes, implications, and the affected gametes differ. The distinction between these two types of nondisjunction is fundamental in the study of genetics, fertility treatments, and understanding the etiology of chromosomal disorders.

Comparison Chart


Occurs during anaphase I
Occurs during anaphase II

Affected Chromosomes

Homologous chromosomes fail to separate
Sister chromatids fail to separate

Resulting Gametes

All gametes affected (2 n+1, 2 n-1)
Half of the gametes affected (1 n+1, 1 n-1, 2 n)

Potential Disorders

Can lead to Down syndrome, Turner syndrome, etc.
Can also lead to similar chromosomal disorders

Frequency of Aneuploid Gametes

Higher, as all gametes from the event are abnormal
Lower, as only half of the gametes from the event are abnormal

Compare with Definitions

Nondisjunction in Meiosis 1

Critical factor in aneuploidy and genetic disorders.
Understanding nondisjunction in Meiosis 1 is crucial for diagnosing and counseling on genetic conditions.

Nondisjunction in Meiosis 2

Occurs when sister chromatids don't separate in meiosis II.
Nondisjunction in Meiosis 2 may cause one gamete to lack a chromosome, leading to monosomy.

Nondisjunction in Meiosis 1

Results from homologues not separating during anaphase I.
The failure of homologous chromosomes to separate during nondisjunction in Meiosis 1 leads to genetic disorders.

Nondisjunction in Meiosis 2

Results in a mix of normal and aneuploid gametes.
Nondisjunction in Meiosis 2 creates a variability in gamete chromosome numbers.

Nondisjunction in Meiosis 1

Error in meiosis leading to uneven division of homologous chromosomes.
Nondisjunction in Meiosis 1 can result in gametes with an extra chromosome 21, causing Down syndrome.

Nondisjunction in Meiosis 2

Can lead to disorders if an abnormal gamete is fertilized.
If a gamete from nondisjunction in Meiosis 2 fertilizes, it can result in a zygote with an abnormal chromosome number.

Nondisjunction in Meiosis 1

Increases risk of chromosomal abnormalities in offspring.
Nondisjunction in Meiosis 1 significantly raises the chances of having children with genetic abnormalities.

Nondisjunction in Meiosis 2

Less likely to affect all offspring compared to Meiosis 1.
The impact of nondisjunction in Meiosis 2 on offspring is less uniform than that of Meiosis 1.

Nondisjunction in Meiosis 1

Causes all resulting gametes to have abnormal chromosome numbers.
Following nondisjunction in Meiosis 1, all produced gametes are aneuploid.

Nondisjunction in Meiosis 2

Affects only half of the resulting gametes.
In nondisjunction in Meiosis 2, two gametes remain normal, while the others are aneuploid.

Common Curiosities

Can nondisjunction be prevented?

Currently, there are no known methods to prevent nondisjunction.

How common is nondisjunction?

It's a relatively common genetic error, increasing with parental age, especially maternal age.

What disorders are caused by nondisjunction in Meiosis 1?

Disorders such as Down syndrome, Patau syndrome, and Edwards syndrome can result from nondisjunction in Meiosis 1.

What causes nondisjunction in meiosis?

Errors in spindle fiber attachment or chromosome cohesion can lead to nondisjunction.

Is nondisjunction more common in Meiosis 1 or Meiosis 2?

It can occur in both, but nondisjunction in Meiosis 1 is often considered more impactful due to all gametes being affected.

Does nondisjunction affect males and females differently?

The risk and type of disorders may vary, but both genders can produce aneuploid gametes due to nondisjunction.

How does maternal age influence nondisjunction?

Increased maternal age is associated with a higher risk of nondisjunction, likely due to aging oocytes.

Are the effects of nondisjunction in Meiosis 2 different from Meiosis 1?

Yes, because Meiosis 2 affects only half of the gametes, leading to a mix of normal and aneuploid gametes.

How is nondisjunction detected?

Prenatal testing methods like amniocentesis and chorionic villus sampling can detect nondisjunction.

Can nondisjunction lead to infertility?

Yes, gametes with an abnormal number of chromosomes may lead to infertility or increased risk of miscarriage.

Can nondisjunction happen in somatic cells?

Nondisjunction primarily concerns gametes, but similar errors in somatic cells can lead to mosaic conditions or cancer.

Can lifestyle factors influence the risk of nondisjunction?

While maternal age is a known factor, the impact of lifestyle on nondisjunction risk is less clear and under investigation.

What is the difference in the outcome of nondisjunction in Meiosis 1 vs. Meiosis 2?

Nondisjunction in Meiosis 1 affects all resulting gametes, while in Meiosis 2, only half of the gametes are affected.

What research is being done on nondisjunction?

Research focuses on understanding its causes, mechanisms, and ways to minimize its impact on fertility and offspring health.

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Author Spotlight

Written by
Tayyaba Rehman
Tayyaba Rehman is a distinguished writer, currently serving as a primary contributor to As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
Co-written by
Urooj Arif
Urooj is a skilled content writer at Ask Difference, known for her exceptional ability to simplify complex topics into engaging and informative content. With a passion for research and a flair for clear, concise writing, she consistently delivers articles that resonate with our diverse audience.

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