Meiosis and Sources of Genetic Variation (1C) - MCAT Biological and Biochemical Foundations of Living Systems
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What is the term for paired homologous chromosomes during prophase I?
What is the term for paired homologous chromosomes during prophase I?
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Tetrad (bivalent). This structure forms when homologs pair, enabling crossing over for genetic recombination.
Tetrad (bivalent). This structure forms when homologs pair, enabling crossing over for genetic recombination.
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Which stage of meiosis separates homologous chromosomes?
Which stage of meiosis separates homologous chromosomes?
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Anaphase I. During this phase, homologous chromosomes are pulled apart to opposite poles, reducing ploidy.
Anaphase I. During this phase, homologous chromosomes are pulled apart to opposite poles, reducing ploidy.
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What is the ploidy change when a diploid cell completes meiosis?
What is the ploidy change when a diploid cell completes meiosis?
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Diploid $2n$ to haploid $n$. Meiosis reduces the chromosome number by half to produce gametes that can restore diploidy upon fusion.
Diploid $2n$ to haploid $n$. Meiosis reduces the chromosome number by half to produce gametes that can restore diploidy upon fusion.
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What is synapsis in prophase I of meiosis?
What is synapsis in prophase I of meiosis?
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Pairing of homologous chromosomes via the synaptonemal complex. Synapsis facilitates close alignment of homologs, allowing crossing over to exchange genetic material.
Pairing of homologous chromosomes via the synaptonemal complex. Synapsis facilitates close alignment of homologs, allowing crossing over to exchange genetic material.
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Which stage of meiosis separates sister chromatids?
Which stage of meiosis separates sister chromatids?
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Anaphase II. Sister chromatids separate in this phase, similar to mitosis, to distribute identical DNA copies.
Anaphase II. Sister chromatids separate in this phase, similar to mitosis, to distribute identical DNA copies.
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What is the primary purpose of meiosis in sexually reproducing organisms?
What is the primary purpose of meiosis in sexually reproducing organisms?
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Produce haploid gametes and increase genetic variation. Meiosis ensures genetic diversity in offspring by halving chromosome number for fertilization and introducing variation through recombination.
Produce haploid gametes and increase genetic variation. Meiosis ensures genetic diversity in offspring by halving chromosome number for fertilization and introducing variation through recombination.
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Which meiotic division is reductional, and what does that mean?
Which meiotic division is reductional, and what does that mean?
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Meiosis I; reduces ploidy by separating homologs. Meiosis I halves the chromosome number by segregating homologous pairs into daughter cells.
Meiosis I; reduces ploidy by separating homologs. Meiosis I halves the chromosome number by segregating homologous pairs into daughter cells.
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What is the key structural difference between homologous chromosomes and sister chromatids?
What is the key structural difference between homologous chromosomes and sister chromatids?
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Homologs: maternal vs paternal; sisters: identical copies after S phase. Homologs differ in parental origin and may have allelic variations, while sisters are replication products.
Homologs: maternal vs paternal; sisters: identical copies after S phase. Homologs differ in parental origin and may have allelic variations, while sisters are replication products.
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If a species has $n=3$, what is the number of possible gamete chromosome combinations from assortment alone?
If a species has $n=3$, what is the number of possible gamete chromosome combinations from assortment alone?
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$2^3=8$. With three pairs, each can assort independently, resulting in $2^3$ unique gamete genotypes from assortment.
$2^3=8$. With three pairs, each can assort independently, resulting in $2^3$ unique gamete genotypes from assortment.
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What is the DNA replication status between meiosis I and meiosis II?
What is the DNA replication status between meiosis I and meiosis II?
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No S phase; DNA is not replicated between divisions. Absence of interphase replication preserves the reduced DNA content for haploid gamete production.
No S phase; DNA is not replicated between divisions. Absence of interphase replication preserves the reduced DNA content for haploid gamete production.
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Which meiotic division is equational, and what does that mean?
Which meiotic division is equational, and what does that mean?
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Meiosis II; separates sister chromatids without changing ploidy. Meiosis II divides chromatids equally, maintaining the haploid state established in meiosis I.
Meiosis II; separates sister chromatids without changing ploidy. Meiosis II divides chromatids equally, maintaining the haploid state established in meiosis I.
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What is the immediate product of meiosis in humans (starting from one primary germ cell)?
What is the immediate product of meiosis in humans (starting from one primary germ cell)?
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Four haploid cells (gametes or gamete precursors). Meiosis yields four genetically distinct haploid cells from one diploid precursor for reproduction.
Four haploid cells (gametes or gamete precursors). Meiosis yields four genetically distinct haploid cells from one diploid precursor for reproduction.
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What is nondisjunction in meiosis?
What is nondisjunction in meiosis?
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Failure of homologs (I) or sister chromatids (II) to separate properly. Nondisjunction leads to aneuploid gametes by improper segregation during meiotic divisions.
Failure of homologs (I) or sister chromatids (II) to separate properly. Nondisjunction leads to aneuploid gametes by improper segregation during meiotic divisions.
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If nondisjunction occurs in meiosis I, what gamete types result in terms of $n$?
If nondisjunction occurs in meiosis I, what gamete types result in terms of $n$?
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Two gametes $n+1$ and two gametes $n-1$. Meiosis I nondisjunction affects both daughter cells, producing equal numbers of hyper- and hypoploid gametes.
Two gametes $n+1$ and two gametes $n-1$. Meiosis I nondisjunction affects both daughter cells, producing equal numbers of hyper- and hypoploid gametes.
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If nondisjunction occurs in meiosis II, what gamete types result in terms of $n$?
If nondisjunction occurs in meiosis II, what gamete types result in terms of $n$?
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Two normal $n$, one $n+1$, and one $n-1$ gamete. Meiosis II nondisjunction impacts only one cell, yielding two normal and two aneuploid gametes.
Two normal $n$, one $n+1$, and one $n-1$ gamete. Meiosis II nondisjunction impacts only one cell, yielding two normal and two aneuploid gametes.
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What is trisomy in terms of chromosome copy number?
What is trisomy in terms of chromosome copy number?
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Three copies of one chromosome (a $2n+1$ condition). Trisomy results from gaining an extra chromosome, often due to nondisjunction, altering the diploid complement.
Three copies of one chromosome (a $2n+1$ condition). Trisomy results from gaining an extra chromosome, often due to nondisjunction, altering the diploid complement.
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Which two meiotic mechanisms are the major sources of genetic variation in gametes?
Which two meiotic mechanisms are the major sources of genetic variation in gametes?
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Crossing over and independent assortment. These processes shuffle alleles and chromosome combinations, ensuring genetic diversity in offspring.
Crossing over and independent assortment. These processes shuffle alleles and chromosome combinations, ensuring genetic diversity in offspring.
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What is independent assortment in meiosis?
What is independent assortment in meiosis?
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Random orientation of homologous pairs at metaphase I. This random alignment ensures each gamete receives a unique combination of maternal and paternal chromosomes.
Random orientation of homologous pairs at metaphase I. This random alignment ensures each gamete receives a unique combination of maternal and paternal chromosomes.
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What is the formula for the number of chromosome combinations from independent assortment?
What is the formula for the number of chromosome combinations from independent assortment?
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$2^n$ (where $n$ is the haploid chromosome number). The formula accounts for each homologous pair having two possible orientations, yielding exponential combinations.
$2^n$ (where $n$ is the haploid chromosome number). The formula accounts for each homologous pair having two possible orientations, yielding exponential combinations.
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Which specific prophase I substage is characterized by crossing over?
Which specific prophase I substage is characterized by crossing over?
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Pachytene. In pachytene, homologs are fully synapsed, enabling enzymes to mediate recombination events.
Pachytene. In pachytene, homologs are fully synapsed, enabling enzymes to mediate recombination events.
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