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

What this deck covers

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.

How to use these flashcards

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 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 2: 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 3: 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 4: 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 5: 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 6: 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 7: 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 8: 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 9: 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 10: 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 11: 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 12: 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 13: 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 14: 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 15: 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 16: 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 17: 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 18: 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 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: 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 21: 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 22: 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 23: 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.

Flashcard 24: 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 25: 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.