Meiosis
51 flashcards covering Meiosis for the MCAT Biology & Biochemistry section.
Meiosis is a type of cell division essential for sexual reproduction, occurring in organisms to create gametes like sperm and eggs. It starts with a cell that has two sets of chromosomes (diploid) and divides twice to produce four cells, each with a single set (haploid). This reduction is crucial to maintain the correct chromosome number in offspring and promotes genetic diversity through events like crossing over and independent assortment. Understanding meiosis helps explain inheritance patterns and evolutionary processes.
On the MCAT, meiosis often appears in biology and biochemistry questions, such as identifying stages, comparing it to mitosis, or analyzing genetic outcomes like recombination. Common traps include confusing the phases or overlooking errors like nondisjunction, which can lead to chromosomal disorders. Focus on key details like the differences between meiosis I and II, and how it drives variation in populations.
Practice labeling meiosis diagrams to solidify your grasp.
Terms (51)
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Meiosis
Meiosis is a type of cell division that produces gametes with half the number of chromosomes as the parent cell, resulting in genetic diversity through processes like crossing over and independent assortment.
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Diploid cell
A diploid cell contains two sets of chromosomes, one from each parent, typically found in somatic cells and the starting point for meiosis in organisms like humans.
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Haploid cell
A haploid cell has a single set of chromosomes, produced at the end of meiosis and found in gametes such as sperm and eggs.
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Homologous chromosomes
Homologous chromosomes are pairs of chromosomes, one from each parent, that carry the same genes in the same order but may have different alleles, and they pair up during meiosis.
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Sister chromatids
Sister chromatids are identical copies of a single chromosome formed during DNA replication, held together at the centromere, and separated during the second division of meiosis.
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Meiosis I
Meiosis I is the first division of meiosis, a reductional division that separates homologous chromosomes, resulting in two haploid cells with duplicated chromosomes.
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Meiosis II
Meiosis II is the second division of meiosis, similar to mitosis, where sister chromatids are separated to produce four haploid cells from the two produced in meiosis I.
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Prophase I
Prophase I is the first stage of meiosis I, where homologous chromosomes pair up, undergo synapsis, and exchange genetic material through crossing over, increasing genetic variation.
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Metaphase I
Metaphase I is a stage in meiosis I where paired homologous chromosomes align at the cell's equator, allowing for independent assortment of maternal and paternal chromosomes.
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Anaphase I
Anaphase I is the stage in meiosis I where homologous chromosomes are pulled apart to opposite poles of the cell, reducing the chromosome number by half.
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Telophase I
Telophase I is the final stage of meiosis I, where the chromosomes arrive at the poles, the nuclear envelope may reform, and the cell prepares to divide into two.
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Prophase II
Prophase II is the first stage of meiosis II, where chromosomes condense again in the two cells from meiosis I, and the spindle apparatus forms for the next division.
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Metaphase II
Metaphase II is a stage in meiosis II where chromosomes align at the equator of each cell, with sister chromatids attached to spindle fibers.
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Anaphase II
Anaphase II is the stage in meiosis II where sister chromatids are separated and pulled to opposite poles, resulting in genetically unique haploid cells.
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Telophase II
Telophase II is the final stage of meiosis II, where chromosomes decondense, nuclear envelopes form around the four haploid nuclei, completing gamete production.
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Crossing over
Crossing over is the exchange of genetic material between homologous chromosomes during prophase I of meiosis, which promotes genetic recombination and diversity.
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Synapsis
Synapsis is the pairing of homologous chromosomes during prophase I of meiosis, facilitated by the synaptonemal complex, allowing for crossing over.
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Tetrad
A tetrad is the structure formed by two homologous chromosomes and their sister chromatids during prophase I of meiosis, where crossing over occurs.
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Chiasma
A chiasma is the point of contact between homologous chromosomes where genetic material is exchanged during crossing over in meiosis.
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Independent assortment
Independent assortment is the random alignment of homologous chromosome pairs during metaphase I of meiosis, leading to varied combinations of chromosomes in gametes.
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Genetic recombination
Genetic recombination in meiosis results from crossing over and independent assortment, creating new allele combinations that increase genetic variation in offspring.
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Nondisjunction
Nondisjunction is an error in meiosis where homologous chromosomes or sister chromatids fail to separate properly, potentially leading to gametes with extra or missing chromosomes.
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Synaptonemal complex
The synaptonemal complex is a protein structure that forms between homologous chromosomes during synapsis in prophase I, holding them together for crossing over.
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Bivalent
A bivalent, or tetrad, refers to the paired homologous chromosomes in meiosis, aligned and ready for segregation during metaphase I.
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Reduction division
Reduction division describes meiosis I, where the chromosome number is halved from diploid to haploid, ensuring the correct chromosome count in gametes.
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Equational division
Equational division refers to meiosis II, where the chromosome number remains the same as it separates sister chromatids, similar to mitosis.
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Gametogenesis
Gametogenesis is the process of forming gametes through meiosis, including spermatogenesis in males and oogenesis in females, to produce sperm and eggs.
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Spermatogenesis
Spermatogenesis is the meiotic process in males that produces four functional sperm from one diploid spermatogonium, occurring in the testes.
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Oogenesis
Oogenesis is the meiotic process in females that produces one mature egg and polar bodies from one diploid oogonium, occurring in the ovaries.
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Polar bodies
Polar bodies are small cells produced during oogenesis in meiosis that contain little cytoplasm and degenerate, ensuring the egg receives most resources.
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Primary oocyte
A primary oocyte is the diploid cell that enters meiosis I in females, developing into a secondary oocyte and eventually an ovum if fertilized.
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Secondary oocyte
A secondary oocyte is the haploid cell produced after meiosis I in oogenesis, which completes meiosis II only upon fertilization.
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Primary spermatocyte
A primary spermatocyte is the diploid cell that undergoes meiosis I in males, dividing to form two secondary spermatocytes.
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Secondary spermatocyte
A secondary spermatocyte is the haploid cell produced after meiosis I in spermatogenesis, which then divides in meiosis II to form spermatids.
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Spermatid
A spermatid is the haploid cell resulting from meiosis II in spermatogenesis, which matures into a functional sperm through spermiogenesis.
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Meiotic spindle
The meiotic spindle is a structure of microtubules that attaches to chromosomes during meiosis, facilitating their movement and separation in both divisions.
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Leptotene
Leptotene is the first substage of prophase I in meiosis, where chromosomes condense and begin to appear as long threads.
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Zygotene
Zygotene is a substage of prophase I where homologous chromosomes start to pair up through synapsis.
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Pachytene
Pachytene is a substage of prophase I where crossing over occurs between homologous chromosomes.
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Diplotene
Diplotene is a substage of prophase I where homologous chromosomes begin to separate but remain attached at chiasmata.
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Diakinesis
Diakinesis is the final substage of prophase I, where chromosomes fully condense and the nuclear envelope breaks down.
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Interkinesis
Interkinesis is the brief period between meiosis I and II, where no DNA replication occurs, and cells prepare for the second division.
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Cytokinesis I
Cytokinesis I is the division of the cytoplasm following meiosis I, resulting in two cells.
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Cytokinesis II
Cytokinesis II is the division of the cytoplasm following meiosis II, producing four haploid cells.
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Recombination frequency
Recombination frequency measures the rate of crossing over between genes during meiosis, used to map gene distances on chromosomes.
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Segregation of alleles
Segregation of alleles during meiosis follows Mendel's law, where alleles for a gene separate into different gametes.
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Linkage and crossing over
Linkage refers to genes on the same chromosome that tend to be inherited together, but crossing over in meiosis can separate them.
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Differences between meiosis and mitosis
Meiosis produces haploid gametes with genetic variation through two divisions, while mitosis produces identical diploid cells for growth and repair.
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Checkpoint in meiosis
Checkpoints in meiosis ensure proper chromosome alignment and DNA repair before proceeding, preventing errors like nondisjunction.
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Aneuploidy
Aneuploidy is an abnormal chromosome number resulting from meiotic errors, such as nondisjunction, leading to conditions like Down syndrome.
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Genetic diversity from meiosis
Meiosis generates genetic diversity through crossing over, independent assortment, and random fertilization, essential for evolution and adaptation.