MCAT Reproduction Flashcards

MCAT Reproduction, Mitosis, and Meiosis Flashcards

What is the ploidy of a primary oocyte?

Diploid (2n), arrested in prophase I at birth.

When is meiosis II completed in oogenesis?

Only if fertilization occurs, otherwise the secondary oocyte remains arrested in metaphase II.

What are polar bodies?

Small cells with minimal cytoplasm formed during oogenesis due to unequal cytokinesis.

What structure surrounds the oocyte and mediates sperm binding?

Zona pellucida (glycoprotein layer).

What hormone is secreted by the hypothalamus to initiate reproduction?

GnRH (gonadotropin-releasing hormone)

What cells in the testes secrete testosterone?

Leydig cells

What cells in the testes nourish developing sperm?

Sertoli cells

Where is sperm stored and matured?

Epididymis

What is the pathway of sperm through the male reproductive tract?

Seminiferous tubules → Epididymis → Vas deferens → Ejaculatory duct → Urethra → Penis

What hormone stimulates Sertoli cells?

FSH

What hormone stimulates Leydig cells?

LH

What does estrogen do to the endometrium?

Stimulates proliferation of the endometrial lining.

What does progesterone do to the endometrium?

Maintains the endometrial lining after ovulation.

What triggers the LH surge?

Rising estrogen levels causing positive feedback on the hypothalamus and anterior pituitary.

What does the LH surge cause?

Ovulation (release of the secondary oocyte from the follicle).

What happens to the ruptured follicle post-ovulation?

Becomes the corpus luteum, which secretes progesterone.

What happens to the corpus luteum if fertilization does not occur?

It atrophies, leading to a drop in progesterone and onset of menstruation.

What hormone maintains the corpus luteum during early pregnancy?

hCG (human chorionic gonadotropin)

What is the function of hCG?

Mimics LH to maintain corpus luteum and progesterone production.

When does hCG production shift to the placenta?

End of the first trimester

What does menopause involve?

Cessation of ovulation due to FSH/LH insensitivity; estrogen/progesterone drop; FSH/LH levels rise.

What is the function of the acrosome in sperm?

Contains enzymes to penetrate the zona pellucida.

What part of the sperm contains mitochondria for motility?

Midpiece

What process creates four nonidentical gametes?

Meiosis

What type of cells does meiosis occur in?

Gametocytes (germ cells)

What phase of meiosis explains Mendel’s First Law (segregation)?

Anaphase I

What phase of meiosis explains Mendel’s Second Law (independent assortment)?

Prophase I (crossing over)

What are the four phases of mitosis?

Prophase, Metaphase, Anaphase, Telophase

What hormone promotes sperm motility and survival in alkaline fluid?

Seminal vesicles and prostate gland contribute fluids, not hormones.

What is the first cell stage in spermatogenesis?

Spermatogonium

What are spermatids?

Haploid cells after meiosis II that mature into spermatozoa.

What does the bulbourethral gland secrete?

Clear fluid to clean urethra and lubricate during arousal.

What structure carries the oocyte from ovary to uterus?

Fallopian tube (oviduct)

What is the site of fertilization?

Ampulla of the fallopian tube.

What is the functional layer of the uterus that sheds during menstruation?

Endometrium

What is the role of the uterine cervix?

Lower end of uterus, opens into vagina; allows sperm entry and childbirth passage.

What happens in the follicular phase?

FSH stimulates follicle growth; estrogen rises; endometrium thickens.

What happens in the luteal phase?

Corpus luteum secretes progesterone; endometrium is maintained.

What hormone is highest just before ovulation?

LH

What hormone peaks in the luteal phase?

Progesterone

What happens if fertilization occurs?

hCG maintains corpus luteum → progesterone production → pregnancy support

What is the acellular layer outside the zona pellucida?

Corona radiata

What is the chromosomal sex determination system in humans?

XX = female, XY = male

What is androgen insensitivity syndrome (AIS)?

XY individual lacks functional androgen receptors → appears female

What cell cycle checkpoint checks DNA quality before S phase?

G1 (restriction point)

What is the diploid number of chromosomes in humans?

46 (2n)

What is nondisjunction?

Failure of homologous chromosomes or sister chromatids to separate properly.

Name a disorder caused by nondisjunction.

Trisomy 21 (Down syndrome)

What type of feedback loop controls most hormone secretion?

Negative feedback

What hormones rise at menopause?

FSH and LH due to loss of estrogen/progesterone negative feedback

What is the goal of mitosis?

To produce two genetically identical diploid (2n) daughter cells for growth and repair.

In what type of cells does mitosis occur?

Somatic cells

What are the stages of mitosis (in order)?

Prophase → Metaphase → Anaphase → Telophase → Cytokinesis

What happens in prophase (mitosis)?

Chromosomes condense, nuclear membrane dissolves, spindle forms.

What happens in metaphase (mitosis)?

Chromosomes align at the metaphase plate.

What happens in anaphase (mitosis)?

Sister chromatids are pulled to opposite poles.

What happens in telophase (mitosis)?

Nuclear envelope reforms, chromosomes de-condense.

What happens in cytokinesis?

The cytoplasm divides → two separate daughter cells form.

What is the goal of meiosis?

To produce four nonidentical haploid (n) gametes.

What are the two divisions of meiosis?

Meiosis I (reductional) and Meiosis II (equational)

What happens in prophase I?

Homologous chromosomes pair up and form a tetrad; crossing over occurs (genetic recombination).

What happens in metaphase I?

Tetrads (homologous pairs) align at the metaphase plate.

What happens in anaphase I?

Homologous chromosomes separate (Mendel’s Law of Segregation).

What happens in meiosis II?

Like mitosis: sister chromatids are separated in anaphase II.

What are the key differences between mitosis and meiosis?

Mitosis: 1 division → 2 identical diploid cells
• Meiosis: 2 divisions → 4 nonidentical haploid cells
• Crossing over only happens in meiosis (prophase I)

What happens in Prophase (Mitosis)?

Chromosomes condense
• Nuclear envelope breaks down
• Centrioles move to poles
• Mitotic spindle forms
• No crossing over occurs

What happens in Metaphase (Mitosis)?

Chromosomes align single-file along the metaphase plate • Spindle fibers attach to centromeres via kinetochores

What happens in Anaphase (Mitosis)?

Sister chromatids are pulled apart to opposite poles by spindle fibers
• Each chromatid is now considered a chromosome

What happens in Telophase (Mitosis)?

Nuclear membrane reforms
• Chromosomes decondense
• Spindle apparatus breaks down

What is Cytokinesis, and when does it occur?

Physical division of the cytoplasm into two cells
• Begins during telophase, finishes after nuclear division
• Involves a cleavage furrow in animal cells