MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 2c Meiosis Gametogenesis

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This deck focuses on 2c Meiosis Gametogenesis, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is nondisjunction, stated as a single definition relevant to meiosis?

Answer: Failure of homologs or sister chromatids to separate. Nondisjunction leads to aneuploid gametes by causing improper chromosome segregation during meiotic divisions.

Flashcard 2: Which meiotic division is reductional, and what does it separate?

Answer: Meiosis I; separates homologous chromosomes. The reductional division halves the ploidy by segregating homologous chromosome pairs, each containing genetic material from one parent.

Flashcard 3: What cellular process must occur before meiosis I so each chromosome has two sister chromatids?

Answer: DNA replication during S phase of interphase. Pre-meiotic DNA replication ensures each chromosome consists of two identical sister chromatids, which is essential for proper alignment and segregation during meiosis I.

Flashcard 4: What is the key outcome of meiosis in terms of ploidy and genetic similarity to the parent cell?

Answer: Four genetically unique haploid cells from one diploid cell. Meiosis halves the chromosome number from diploid to haploid while generating genetic diversity through recombination and independent assortment, resulting in non-identical daughter cells.

Flashcard 5: What is synapsis, and during which meiotic stage does it occur?

Answer: Pairing of homologs in prophase I. Synapsis facilitates close alignment of homologous chromosomes, enabling crossing over and genetic recombination during early meiosis.

Flashcard 6: Which meiotic division is equational, and what does it separate?

Answer: Meiosis II; separates sister chromatids. The equational division maintains ploidy by segregating replicated chromatids, similar to mitosis, after the reduction in meiosis I.

Flashcard 7: Which meiotic stage is when homologous chromosomes separate to opposite poles?

Answer: Anaphase I. Homolog separation during this stage reduces ploidy, with each daughter cell receiving one chromosome from each pair.

Flashcard 8: Which meiotic stage is when sister chromatids separate to opposite poles?

Answer: Anaphase II. Sister chromatid separation during this stage produces haploid cells by dividing the replicated chromosomes without further ploidy reduction.

Flashcard 9: What is independent assortment, and at which stage does it arise?

Answer: Random homolog orientation at metaphase I. Independent assortment generates genetic variability by randomly distributing maternal and paternal homologs to daughter cells.

Flashcard 10: What is the formula for the number of possible gamete types from independent assortment alone in a diploid cell?

Answer: $2^n$ (where $n$ is the haploid number). This formula accounts for the random segregation of each homologous pair, yielding $2^n$ unique combinations without considering crossing over.

Flashcard 11: If a species has haploid number $n = 4$, what is the number of gamete types from independent assortment alone?

Answer: $2^4 = 16$. With four chromosome pairs, independent assortment allows for 16 unique gamete genotypes due to random homolog distribution.

Flashcard 12: If nondisjunction occurs in meiosis I, what types of gametes result regarding chromosome number?

Answer: Two $n+1$ and two $n-1$ gametes. Meiosis I nondisjunction affects all gametes by sending both homologs to one pole, resulting in equal numbers of hyperploid and hypoploid cells after meiosis II.

Flashcard 13: If nondisjunction occurs in meiosis II, what types of gametes result regarding chromosome number?

Answer: One $n+1$, one $n-1$, and two normal $n$ gametes. Meiosis II nondisjunction affects only half the products, producing one hyperploid, one hypoploid, and two euploid gametes.

Flashcard 14: What is the chromosome number in a zygote formed by fertilization of two normal haploid gametes?

Answer: $2n$ (diploid). Fertilization restores diploidy by combining two sets of haploid chromosomes from parental gametes.

Flashcard 15: What is the chromosome number in a zygote formed by an $n+1$ gamete fertilized by a normal $n$ gamete?

Answer: $2n+1$ (trisomy). Fusion of an aneuploid gamete with extra chromosome and a normal one results in a zygote with three copies of that chromosome.

Flashcard 16: What is the chromosome number in a zygote formed by an $n-1$ gamete fertilized by a normal $n$ gamete?

Answer: $2n-1$ (monosomy). Fusion of an aneuploid gamete missing a chromosome and a normal one results in a zygote with only one copy of that chromosome.

Flashcard 17: What is the key distinction between homologous chromosomes and sister chromatids?

Answer: Homologs are maternal vs paternal; sisters are identical copies. Homologous chromosomes carry the same genes but may differ in alleles due to parental origin, whereas sister chromatids are exact replicas post-replication.

Flashcard 18: What is spermatogenesis in terms of starting cell and final number of functional gametes?

Answer: One primary spermatocyte yields four sperm. Spermatogenesis involves equal cytoplasmic division in meiosis, producing four viable haploid sperm from one diploid precursor.

Flashcard 19: What is oogenesis in terms of starting cell and final number of functional gametes?

Answer: One primary oocyte yields one ovum plus polar bodies. Oogenesis features unequal cytokinesis, concentrating cytoplasm in one cell to form a functional egg while discarding polar bodies.

Flashcard 20: Which meiotic arrest occurs in human oocytes before ovulation, and at what stage is it arrested?

Answer: Arrest in prophase I (dictyotene) until puberty. This prolonged arrest in females preserves oocytes from fetal development until reproductive maturity, resuming in selected follicles each cycle.

Flashcard 21: Which meiotic arrest occurs in a human secondary oocyte after ovulation, and when is meiosis completed?

Answer: Arrest in metaphase II; completed at fertilization. The secondary oocyte halts at this stage post-ovulation to await sperm penetration, which triggers completion of meiosis II and polar body extrusion.

Flashcard 22: What is a tetrad (bivalent) in meiosis?

Answer: Paired homologs containing four chromatids total. A tetrad forms from synapsed homologous chromosomes, each with two chromatids, allowing for genetic exchange via crossing over.

Flashcard 23: What is a chiasma in meiosis?

Answer: Visible crossover point between nonsister chromatids. Chiasmata represent sites of genetic recombination where nonsister chromatids have exchanged segments, holding homologs together until anaphase I.

Flashcard 24: Which meiotic stage is defined by crossing over and recombination between homologous chromosomes?

Answer: Prophase I. Crossing over during this stage exchanges genetic material between nonsister chromatids, increasing genetic variation in gametes.

Flashcard 25: Which meiotic stage features tetrads aligned at the metaphase plate with random orientation?

Answer: Metaphase I. Tetrads align randomly at the equator, contributing to independent assortment and genetic diversity in resulting gametes.