Name: meiosis and the making of gametes
Uploaded: 2021-04-07T12:12:02.000Z
Duration: 2 min 28 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

What is Meiosis?

In humans, diploid germ cells in the testes and ovaries produce haploid sperm and egg cells through meiosis. Meiosis consists of two successive cell divisions. The first division is a reductional division, in which the chromosome number is reduced from diploid to haploid. The second division is an equational division, in which the chromosome number remains unchanged, producing four haploid cells.The first division is meiosis I, which begins with diploid cells containing replicated homologous chromosomes. These are corresponding maternal and paternal chromosomes that carry the same genes. Each chromosome appears X-shaped because it contains two identical sister chromatids joined at the centromere.During this stage, maternally and paternally inherited chromosomes pair and exchange genetic material through crossing over, creating genetic diversity.After the nuclear membrane disintegrates, the chromosomes move into the cytoplasm. Spindle fibers, microtubule-based structures, attach to the chromosomes, separate them, and distribute them randomly and evenly between opposite ends of the cell before division.The result is two genetically unique haploid cells.Importantly, although each X in

what is meiosis?

Meiosis is the process by which diploid cells divide to produce haploid daughter cells. In humans, each diploid cell contains 46 chromosomes, half from the mother and half from the father. Following meiosis, the resulting haploid eggs or sperm only contain 23 chromosomes; however, each of these chromosomes contains a unique combination of parental information that results from the meiotic process of crossing over.

Although meiosis shares similarities with mitosis&#x2014;both rely on microtubules to partition chromosomes to opposite sides of a cell, which then divides to form a daughter cell pair&#x2014;meiosis is only observed in the sex organs, while mitosis occurs in other tissue types of the body. In addition, the cells resulting from mitosis are genetically indistinguishable (save for random mutations) from their predecessor: crossing over does not occur, and all the daughter cells are diploid. In contrast, meiosis produces four cells that not only have half the number of chromosomes from their predecessor, but they also contain unique combinations of genetic material. No two meiotic products are identical, which helps account for the appearance and personality differences often seen between siblings in the same family.

Meiosis is the process by which diploid cells divide to produce haploid daughter cells. In humans, each diploid cell contains 46 chromosomes, half from ...

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Education

JoVE Core

Molecular Biology

Unit 2

Meiosis

KEY TERMS AND CONCEPTS

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 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

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...

key terms and concepts

Explore meiosis as the cell division process that makes gametes, reduces chromosome number, and supports sexual reproduction in high school biology.

Meiosis and the Making of Gametes | JoVE K12

molecular biology

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Biology

Heredity

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Meiosis and the Making of Gametes

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