Chapter 13- Meiosis Flashcards by Reginald S

Meiosis reduces the number of

chromosomes

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A process where a single cell divides twice to produce four cells containing half the original amount of genetic information. These cells are our sex cells – sperm in males, eggs in females.

meiosis

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Sexual reproduction requires

meiosis

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Cell division that reduces chromosome number by half

meiosis

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A haploid reproductive cell.

Gametes (eggs and sperm) each contained two chromosomes

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Any of the cells of a multicellular organism except those that are destined to form gametes (germ-line cells).

Somatic cells (non reproductive cells)

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Normal mitotic cell: ___________

Cell after completion of meiosis: _________

2n (diploid)

n (haploid)

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reproductive cells (n) _______________

nonreproductive cells (2n) _____________

Gametes

Somatic cells

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An egg and a sperm (gametes), each containing half the complement of chromosomes found in other cells, fuse to produce a single cell called a

zygote

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_________ can fuse and form a zygote (2n) in a process called_________

gametes

fertilization

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The diploid (2n) cell resulting from the fusion of male and female gametes (fertilization).

zygote

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The fusion of gametes to form a new cell is called

fertilization

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Special reduction division, occurs during gamete formation, producing cells with half the normal number of chromosomes.

meiosis

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Meiosis and fertilization together constitute a

cycle of reproduction

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Two sets of chromosomes are present in the somatic cells of adult individuals, making them _______ cells, but only one set is present in the gametes, which are thus ________

diploid

haploid

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Alternation of 2n and n via meiosis, fusion, and mitosis

sexual reproduction

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Reproduction that involves alternation of meiosis and fertilization is called

sexual reproduction

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Offspring inherit chromosomes from____________, You, for example, inherited ___ chromosomes from your mother (maternal homologue), and ___ from your father (paternal homologue).

two parents

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In animals, the single diploid zygote undergoes________ to give rise to all of the cells in the adult body

mitosis

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Somatic cells undergo mitosis to form genetically identical,_________________

diploid daughter cells

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Both somatic cells and germline cells are __________

diploid

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Germ-line cells can undergo _______ to produce ____________

meiosis

haploid gametes

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The life cycles of all sexually reproducing organisms follow a pattern of alternation between

diploid and haploid chromosome numbers,

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1) Single zygote cell will undergo _________ and eventually give rise to __________________
2) Cells that will eventually undergo meiosis to produce gametes are set aside from somatic cells early in the course of development

mitosis
all the cells of the body

germ-line cells

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In animals, the zygote first undergoes mitosis to produce _______ cells. Then later in the life cycle, some of these ______ cells undergo meiosis to produce _______ gametes

diploid diploid haploid

Many types of algae, spend the majority of their life cycle in a _________ state.

haploid

in algae, the zygote undergoing meiosis produces ________ cells that then undergo mitosis.

haploid

During zygote development, cells that are set aside from the somatic cells and that will eventually undergo meiosis to produce gametes.

germ-line cells

Meiosis in a diploid organism consists of two rounds of division, called

Meiosis 1 and meiosis 2

The first round of cell division in meiosis; it is referred to as a “reduction division” because homologous chromosomes separate, and the daughter cells have only the haploid number of chromosomes.

meiosis I

The second round of division in meiosis, during which the two haploid cells from meiosis I undergo a mitosis-like division without DNA replication to produce four haploid daughter cells.

meiosis II

Stages of meiosis 1

Interphase 1, Prophase 1 Metaphase 1 Anaphase 1

In this stage of meiosis 1 chromosomes duplicate, forming sister chromatids

Interphase 1,

In this stage of meiosis 1 sister chromatids are attached by a cohesion complex

Interphase 1,

This stage of meiosis 1 like mitosis, has G1, S, and G2 phases

Interphase 1,

In this stage of meiosis 1 the nuclear envelope degrades

Prophase 1

In this stage of meiosis 1 homologous chromosomes group together to form tetrads: called synapsis

Prophase 1

In this stage of meiosis 1___________holds homologous chromosomes together

Synaptonemal complex

Homologous chromosomes pair ________in meiosis

early

During early prophase I of meiosis, homologous chromosomes find each other and become closely associated, a process called ________ or _________

pairing, or synapsis

Homologous chromosomes pair during ____________ This process is called ___________

prophase I of meiosis. synapsis

Produces paired homologues connected by a structure called the synaptonemal complex

synapsis

Sturcture that joins the paired homologues in early prophase 1

The synaptonemal complex

Consists of a central element connected by filaments to two sets of lateral elements that interact with the homologues.

The synaptonemal complex

This process literally allows the homologues to exchange chromosomal material.

recombination, or crossing over

paired homologous chromosomes will exchange chromosomal material via chiasma(ta)

Genetic recombination (crossing over)

a point at which paired chromosomes remain in contact during the first metaphase of meiosis, and at which crossing over and exchange of genetic material occur between the strands.

chiasma

Each chiasma contains _________________, which probably contain enzymes to break and reattach chromatids

recombination modules

recombination modules contain

enzymes to break and reattach chromatids

After recombination, the | ________________breaks down and is loosely attached via chiasmata

synaptonemal complex

After ______________, the synaptonemal complex | breaks down and is loosely attached via chiasmata

recombination

In this stage of meiosis 1 homologous chromosomes line up at the center and spindle complex forms

Metaphase 1

In this stage of meiosis 1 orientation of sister chromosome + homologous chromosome pair is random

Metaphase 1

________ is characterized by the pairing of homologous chromosomes during prophase I. In many species, an elaborate structure called the ___________________ forms between homologues. During this pairing, homologues may exchange chromosomal material at sites called __________. In meiosis I, the homologues separate from each other, reducing the chromosome number to the __________ state (thus the reductive division). It is followed by a second division without replication, during which sister chromatids become separated. The result of meiosis I and II is ________________.

meiosis synaptonemal complex chiasmata haploid state four haploid cells

The first meiotic division is termed the __________________—it results in ____________ that contain one ___________ from each chromosome pair. The second meiotic division does not further reduce the _______________; it will merely separate the ______________ for each homologue.

reduction division daughter cell homologue number of chromosomes sister chromatids

Involves two successive divisions with no replication of genetic material between them

meiosis

consists of two divisions with one round of DNA replication

meiosis

In meiosis DNA replication must be suppressed between the _______________ Because of the behavior of chromosomes during meiosis I, the resulting cells contain _________________ of each chromosome. ________________ acts like mitosis, without DNA replication, converts these cells into ones with a single copy of each chromosome.

two meiotic divisions one replicated copy 2nd meiotic division

like mitosis with no chromosome duplication.

2nd meiotic division

In this stage of meiosis 1 homologous chromosomes are pulled apart to opposite ends

Anaphase 1

In this stage of meiosis 1, meiosis-specific cohesin complex degrades; sister chromatids only attached at the centromere

Anaphase 1

This stage of meiosis 1 is the end of meiosis I

Telophase I

In this stage of meiosis 1, only sister chromatids exist in each daughter cell, and they are no longer identical

Telophase I

Stages of meiosis 2

Prophase II Metaphase II Anaphase II Telophase II

Briefly describe meiosis 2

Cell division without DNA replication

Stages of meiosis 2: what phase? Nuclear membrane degrades again; formation of new spindle

Prophase II

Stages of meiosis 2: what phase? Spindle moves to opposite ends of the cell; chromosomes line up in the center

Metaphase II

Stages of meiosis 2: what phase? Spindle fibers bind to kinetochores of sister chromatids on opposite sides

Metaphase II

Stages of meiosis 2: what phase? Spindle fibers from opposite poles bind to kinetochores of each sister chromatid, allowing each chromosome to migrate to the metaphase plate as a result of tension on the chromosomes from polar microtubules pulling on sister centromeres

Metaphase II

Stages of meiosis 2:what phase? Spindle fibers contract; cohesin complex between sister chromatids completely degraded, sister chromatids then separate to opposite ends

Anaphase 2

Stages of meiosis 2:what phase? The spindle fibers contract, and the cohesin complex joining the centromeres of sister chromatids is finally destroyed, allowing sister chromatids to be pulled to opposite poles.

Anaphase 2

Stages of meiosis 2: what phase? Cell pinches off into two cells; nuclear envelope reforms

Telophase II

Stages of meiosis 2: what phase? The nuclear envelope re-forms around the four sets of daughter chromosomes. Cytokinesis then follows.

Telophase II

The final result of this division is four cells, each containing a complete haploid set of chromosomes

Meiosis 2 division

Meiosis vs Mitosis: Features 1. Homologous pairing of chromosomes _____________ 2. No homologous pairing of chromosomes _____________ 3. Recombination / crossing over during meiosis I _______________ 4. No crossing over_______________ 5. Sister chromatids connected via centromere during anaphase I (while homologous chromosomes separate) __________________ 6. Sister chromatids are pulled apart in anaphase__________ 7. Kinetochores of sister chromatids attached to same pole (microtubule attachment) ______________ 8. Kinetochores attach to opposite poles of sister chromatids _________________ 9. Cell division occurs twice after initial DNA replication______________ 10. DNA replication is repressed during meiosis I and II ______________ 11. Cell division only occurs once after initial DNA replication ___________________ 12. Daughter cells are not identical, random orientation of chromosomes, crossing over, results in variations in offspring, allows for evolution _____________ 13. Daughter cells are identical ______________

1. meiosis 2. mitosis 3. meiosis 4. mitosis 5. meiosis 6. mitosis 7. meiosis 8. mitosis 9. meiosis 10. meiosis 11. mitosis 12. meiosis 13. mitosis

Characterized by homologue pairing and crossing over; by loss of sister chromatid cohesion in the arms, but not at the centromere at the first division; by the suppression of DNA replication between the two meiotic divisions; and by sister kinetochores attachment to the same pole of the spindle.

meiosis

No homologous pairing of chromosomes _____________

mitosis

Daughter cells are not identical, random orientation | of chromosomes, crossing over, results in variations in offspring, allows for evolution _____________

meiosis

Cell division only occurs once after initial DNA replication ___________________

mitosis

Daughter cells are identical ______________

mitosis

DNA replication is repressed during meiosis I and II ______________

meiosis

Kinetochores attach to opposite poles of sister chromatids _________________

mitosis

Cell division occurs twice after initial DNA replication______________

meiosis

No crossing over_______________

mitosis

Sister chromatids connected via centromere during anaphase I (while homologous chromosomes separate) __________________

meiosis

Sister chromatids are pulled apart in anaphase__________

mitosis

Recombination / crossing over during meiosis I _______________

meiosis

Homologous pairing of chromosomes _____________

meiosis