Name: chromosome segregation errors
Uploaded: 2021-04-07T12:12:02.000Z
Duration: 2 min 14 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

from-molecules-to-organisms-structures-and-processes

From Molecules To Organisms: Structures And Processes

HS-LS1-4

Nondisjunction

Human meiosis is highly regulated, but chromosomes can sometimes fail to separate properly during cell division. This error, called nondisjunction, produces gametes with missing or extra chromosomes.During meiosis, chromosomes or chromatids can fail to separate properly. These errors can result from incorrect homologous chromosome pairing, defects in homologous recombination, problems with cohesin proteins, or improper spindle fiber attachment.During normal anaphase I of meiosis I, homologous chromosomes separate and move toward opposite poles. Sometimes, nondisjunction causes both homologous chromosomes to move to the same pole instead of separating.After meiosis II is complete, nondisjunction during meiosis I produces four cells with abnormal chromosome numbers. Two cells receive an extra chromosome, while the other two cells are missing that chromosome.Nondisjunction can also happen during anaphase II of meiosis II. Normally, at this stage, sister chromatids separate and move to opposite poles. During nondisjunction, sister chromatids may fail to separate properly.At the end of meiosis II, four cells are produced. Two cells have normal chromosome numbers, while one cell contains

nondisjunction

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed sister chromatid separation during meiosis II. In some species, notably plants, nondisjunction can result in an organism with an entire additional set of chromosomes, which is called polyploidy. In humans, nondisjunction can occur during male or female gametogenesis and the resulting gametes possess one too many or one too few chromosomes.When an abnormal gamete fuses with a normal gamete, the resulting zygote has an abnormal number of chromosomes and is called aneuploid. An individual with one too few chromosomes has monosomy (45; 2n-1), while trisomy is the presence of one too many chromosomes for a total of 47 (2n+1). Down Syndrome is one well-studied trisomy, where individuals have three copies of chromosome 21. Aneuploid zygotes account for around 70% of spontaneous abortions during gestation.Nondisjunction is more common in sex chromosomes than autosomes. Individuals can have a variety of sex chromosome combinations, including one or more additional sex chromosomes (e.g., XXY, XXX, XYY) or the presence of only a single sex chromosome (denoted X0). These individuals tend to have normal lifespans, though with sometimes major physiological and reproductive consequences. Nondisjunction appears to be more common when homologous chromosomes fail to recombine. Interestingly X and Y chromosomes normally undergo less recombination compared to autosomes, perhaps explaining the frequency of nondisjunction in sex chromosomes. Mutations in synaptonemal complex proteins, which attach homologous chromosomes, reduce crossing over but apparently increase nondisjunction. This suggests that proper chromosome recombination is an important step in normal meiosis.Nondisjunction is more frequent during oogenesis than during spermatogenesis. Postzygotic nondisjunction, a failure of mitotic chromatid separation in the early zygote, causes similar consequences to that of meiotic nondisjunction and accounts for around 2% of Down Syndrome cases. Mitotic nondisjunction is also a hallmark of many human cancers.

During meiosis, chromosomes occasionally separate improperly. This occurs due to failure of homologous chromosome separation during meiosis I or failed ...

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Education

JoVE Core

Molecular Biology

Unit 2

Meiosis

KEY TERMS AND CONCEPTS

chromosome segregation errors

Nondisjunction is a chromosome segregation error during cell division. It happens when chromosomes do not separate the way they should. This mistake can affect the chromosome number in the cells that are formed.

The error can occur during meiosis or mitosis. In meiosis, nondisjunction may lead to gametes with too many or too few chromosomes. In mitosis, it can affect body cells after division. These changes can disrupt normal chromosome balance.

Nondisjunction is an important idea in genetics because it helps explain how chromosome number changes can happen. It is often discussed when studying cell division, chromosome movement, and aneuploidy. Aneuploidy is a condition in which cells have an abnormal number of chromosomes.

Chromosome Segregation Errors

what is meiosis?

Meiosis and the Making of Gametes

Meiosis is the cell division process that makes gametes, or sex cells. It uses one round of DNA replication followed by two divisions. The result is cells with half the usual number of chromosomes. This process matters because it prepares cells for sexual reproduction. It also helps maintain the correct chromosome number when sperm and egg combine. In many organisms, meiosis is a key step in forming haploid cells.

meiosis i

Homolog Pairing and Recombination in Meiosis I

Meiosis I is the stage of meiosis when homologous chromosomes pair, exchange DNA, and reduce the chromosome number by half. It helps form haploid sperm and eggs in animals through cell differentiation. This first division is the step that separates the two sets of chromosomes. Prophase I is the longest and most complex part of meiosis I. During this stage, homologous chromosomes undergo synapsis, which means they pair closely together. The synaptonemal complex, a protein structure, helps make...

meiosis ii

Meiosis II in Gamete Formation

Meiosis II is the second cell division in meiosis and it separates sister chromatids. This division turns haploid cells into four unique haploid gametes. Its stages are similar to mitosis, but meiosis II happens in haploid cells, while mitosis happens in diploid cells. The timing of meiosis II is different in males and females. In male meiosis, centrosomes help form the meiotic spindle. In oocytes from humans, Drosophila, and mice, the spindle forms without centrosomes. In mammalian oocytes,...

crossing over

Crossing Over in Meiosis

Crossing over is an important step in meiosis. It happens during prophase I, when homologous chromosomes pair up closely. This pairing lets matching DNA segments exchange places. The exchange occurs between non-sister chromatids of homologous chromosomes. The result is a new combination of genetic material. This process helps create genetic variation in the cells that are formed. Crossing over works together with chromosome pairing and separation during meiosis. It is a key reason offspring...

meiosis vs. mitosis

Mitosis and Meiosis Differences

Mitosis and meiosis are cell division processes with different jobs in the body. Mitosis supports growth and development by dividing somatic cells. Meiosis divides germ cells and is essential for sexual reproduction. Before mitosis and before meiosis I, the cell copies its DNA. This creates two homologous copies of each chromosome. High cyclin-dependent kinase, or CDK, activity then blocks DNA synthesis by stopping pre-replicative complex formation. That is why DNA replication does not begin...

Nondisjunction is a chromosome segregation error during cell division. It happens when chromosomes do not separate the way they should. This mistake can affect the chromosome number in the cells that are formed. The error can occur during meiosis or mitosis. In meiosis, nondisjunction may lead to gametes with too many or too few chromosomes. In mitosis, it can affect body cells after division. These changes can disrupt normal chromosome balance. Nondisjunction is an important idea in genetics...

key terms and concepts

Learn how nondisjunction happens during meiosis or mitosis and how chromosome separation errors can change chromosome number in cells.

Chromosome Segregation Errors | JoVE K12

molecular biology

JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Biology

Heredity

Structure and function of DNA in cells

Tennessee Academic Standards

BIO1.LS3.1

Virginia  Standards of Learning

HIgh School

BIO.5

BIO.5.d

Minnesota Academic Standards in Science

Life Science

4.1.1 9L.3.2.1.5

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance and Variation of Traits

HS-LS3-2

Next Generation Science Standards

Texas Essential Knowledge and Skills

BIO.8

BIO.8.A

new-york-state-science-learning-standards

New York State Science Learning Standards

Inheritance and Variation of Traits

HS-LS3-1.

Georgia Standards of Excellence

SB2.b

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Chromosome Segregation Errors

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