Chapter 04.3: Meiosis Produces Haploid Germ Cells, The Gametes

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somatic cells

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mitotically dividing and G0 arrested cells; descendants continue to make up the vast majority of each organism's tissues throughout the lifetime of the individual

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germ cells

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cells destined for a specialized role in the production of gametes

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What would happen if gametes were diploid and not haploid?

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The number of chromosomes would double in each successive generation; this would cause a lethal and exponential increase

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What are the names for the two successive nuclear divisions of meiosis?

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meiosis I, meiosis II

or division I of meiosis and division II of meiosis

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What happens during each round of meiosis?

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the cell passes through a prophase, metaphase, anaphase, and telophase, then cytokinesis

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aberrant

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deviating from the ordinary, usual, or normal type

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What happens in prophase I, leptotene?

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-chromosomes thicken and become visible, but the chromatids remain invisible
-centrosomes begin to move toward opposite poles

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What happens in prophase I, zygotene?

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-homologous chromosomes enter synapsis
-the synaptonemal complex forms

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What happens in prophase I, pachytene?

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-synapsis is complete
-crossing-over, genetic exchange between nonsister chromatids of a homologus pair occurs

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What happens in prophase I, diplotene?

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-synaptonemal complex dissolves
-A tetrad of four chromatids is visible
-Crossover points appear as chiasmata, which hold nonsister chromatids together
-Meiotic arrest occurs at this time in many species

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What happens in prophase I, diakinesis?

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-chromatids thicken and shorten
-At the end of prophase I, the nuclear membrane breaks down and the spindle begins to form?

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What are the five sub-stages of prophase I?

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leptotene, zygotene, pachytene, diplotene, diakinesis

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What happens during metaphase I?

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-tetrads line up along the metaphase plate
-Each chromosome of a homologous pair attaches to fibers from opposite poles
-sister chromatids attach to fibers from the same pole

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What happens during anaphase I?

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-The centromere does not divide
-The chiasmata migrate off chromatid ends
-Homologous chromosomes move to opposite poles

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What happens during telophase I?

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-The nuclear envelope re-forms
-Resultant cells have half the number of chromosomes, each consister of two sister chromatids

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When does interkinesis happen?

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after telophase I

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What happens during interkinesis?

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-This is similar to interphase with one important exception: NO chromosomal duplication takes place
-In some species, the chromosomes decondense; in others, they do not

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What happens during prophase II?

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-chromosomes condense
-Centrioles move toward the poles
-The nuclear envelope breaks down at the end of prophase II

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What happens during metaphase II?

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-Chromosomes align at the metaphase plate
-Sisterchromatids attach to spindle fibers from opposite poles

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What happens during telophase II?

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-Chromosomes begin to uncoil
-Nuclear envelopes and nucleoli re-form

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What happens during cytokinesis?

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-The cytoplasm divides, forming four new haploid cells

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How many haploid cells are formed from meiosis?

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four

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Until ovulation, what phase are female germ cells in?

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prophase I

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leptonene

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first definable substage of prophase I; thin chromosomes begin to thicken

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zygotene

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each chromosome seeks out its homologous partner and become zippered together in a process known as synapsis

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synaptonemal complex

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the "zipper" protein structure during the synapsis process, seen in zygotene

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juxtapose

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to place close together or side by side, esp. for comparison or contrast.

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bivalent

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synapsed chromosome pair (because it encompasses two chromosomes)
(because it contains four chromatids, which, as meiosis proceeds, will be parcelled out, one to each of the four

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bivalent may also be referred to as:

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tetrad

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tetra-

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prefix for "four"

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when and where does the recombination nodule appear?

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begin to appear along the synaptonemal complex during pachytene;

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The other term for crossing-over is:

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recombination

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diplotene

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dissolution of the synaptonemal zipper complex

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chiasmata

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represent the sites where crossing-over occurred

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reduction division

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Because the number of chromosomes is reduced to one half the normal diploid number, meiosis I is often called a reductional division

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interkinesis

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brief interphase between meiosis I and meiosis II

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equational division

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a term for meiosis II; this is because at the end of meiosis II each daughter cell has the same number of chromosomes as the parental cell present at the beginning of this division

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aberration

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the act of deviating from the ordinary, usual, or normal type

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nondisjunction

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when the homologs of a chromosome pair do not segregate during meiosis I

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mule

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horse + donkey

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Variation resulting from the independent assortment of nonhomologous chromosomes increases with _____

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the number of chromosomes in the genome

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mitosis occurs in all types of _______cells

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eukaryotic

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meiosis occurs only in ____ organisms

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sexually reproducing

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germ cells

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collective term for embryonic germ cells