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

What is the correct developmental sequence of human embryogenesis?

Fertilization → Morula formation → Blastulation → Gastrulation → Neurulation.

What happens during morula formation?

The zygote undergoes successive mitotic divisions (cleavage), forming a solid ball of cells called the morula.

What is blastulation?

The morula becomes a hollow ball of cells called the blastocyst, which implants in the uterus.

What happens during gastrulation?

The blastocyst forms three germ layers (ectoderm, mesoderm, endoderm) after developing a primitive streak for cell migration.

What structure initiates the formation of the nervous system during neurulation?

The notochord releases signals causing the ectoderm to form the neural plate, which folds to create the neural tube.

What structures arise from the neural crest cells?

Most of the peripheral nervous system.

The female reproductive system is responsible for ?

for producing female gametes (ie, ova) and protecting, nourishing, and providing support to a developing embryo and fetus.

The ovaries are reproductive organs that produce oocytes (immature gametes) via and secretes?

oogenesis and secrete hormones (eg, estrogens, progesterone, inhibin).

The uterine tubes (fallopian tubes, oviducts) are tubes ?

connecting each ovary to the uterus and are the typical location of fertilization

The uterus

• muscular organ responsible for protecting and nourishing the embryo and fetus.
  
  The uterus is lined with an inner layer called the endometrium, which changes in thickness at different points in the monthly uterine cycle.
  
  The uterus also includes a thick layer of smooth muscle (ie, myometrium) involved in contractions during childbirth.

The cervix

the most inferior portion of the uterus and serves as the opening into the vagina.
During childbirth, the cervix thins and the fetus passes through the cervix into the vagina.

The type of muscle the uterus contains is?

smooth muscle that lacks striations, unlike skeletal and cardiac muscle.

As part of the female reproductive system, the uterus nourishes?

the embryo and fetus. It is lined with endometrium, includes a layer of smooth muscle called myometrium, and connects to the vagina at the cervix

The ovarian cycle

(ie, events that occur during maturation of a primary oocyte) can be divided into three phases: the follicular phase (days 1-13), ovulation (day 14), and the luteal phase (days 15-28). During the follicular phase, stimulation of the hypothalamic-pituitary-gondal (HPG) axis results in the release of gonadotropin-releasing hormone by the hypothalamus. This causes the anterior pituitary to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which stimulate the follicles developing in the ovaries to release estrogen.

These estrogens initially inhibit their own production by the HG axis, but the emergence of a dominant ovarian follicle stimulates high estrogen secretion. The higher levels of estrogen stimulate, rather than inhibit, the HPG axis later in the follicular phase and cause a surge of LH (and FSH, to a lesser extent). Ovulation occurs soon after the LH surge from the anterior pituitary. A mature follicle ruptures and the secondary oocyte is released into the abdominal cavity, where it enters a nearby uterine tube.

The final phase of the ovarian cycle, or the luteal phase, is marked by conversion of the ruptured ovarian follicle to the corpus luteum, which secretes high levels of progesterone and estrogen and exerts negative feedback on the HPG axis. If fertilization does not occur, the corpus luteum degenerates and progesterone and estrogen levels decline, allowing the next ovarian cycle to begin.

Following fertilization in multicellular organisms, the single-celled zygote is?

is totipotent, or able to develop into any of the cells or tissues of the organism.

cell determination.

Once cell division begins, the resulting embryonic cells become progressively restricted in their developmental fates,

during gastrulation the three germ layers are formed:

mesoderm, and endoderm) are formed. Afterward, ectodermal cells are restricted to becoming either surface ectoderm, neural crest, or neural tube.

Once the cell's fate has been determined, a program of cell differentiation allows for the formation of ?

of specialized tissues and cell types. During cell differentiation, differential gene expression patterns result in the specific features (eg, size, morphology, metabolic characteristics) of that cell type. For example, ectodermal cells specialize into specific cell types within that germ layer (eg, epidermis, neurons, melanocytes).

Differences in gene expression, due to both internal and external factors, drive the ?

the cell differentiation process.

Internal factors do not depend on interactions of cells with each other or with their environment, and result from inherent differences among individual cells.

External factors influencing cell differentiation involve interactions with neighboring cells and the environment surrounding the cell.

In embryonic cells, asymmetric distribution of transcription factors to embryonic daughter cells leads to production of ?

daughter cells containing different transcription factors following cell division. Receipt of these different transcription factors causes daughter cells cells to display differential gene expression, which is an example of a mechanism of cell differentiation due to an internal factor.

Other examples of internal factors include epigenetic modifications such as DNA methylation or chromatin remodeling.

Direct contact between adjacent cells and secretion of short- and longer-range signaling molecules trigger ?

signaling cascades that result in differential expression or repression of certain genes. In addition, environmental effects (eg, differences in oxygen levels) can differentially affect gene expression as well.

Sperm reaches oocyte:

The sperm weaves past follicular cells of the corona radiata.

Sperm contact:

The sperm binds receptors in the zona pellucida, a thick matrix of glycoproteins that surrounds the oocyte.

Acrosome reaction:

The acrosome is a specialized vesicle filled with hydrolytic enzymes, located in the sperm head. When these enzymes are released, the zona pellucida is degraded, enabling the sperm to reach the oocyte's plasma membrane.

Fusion:

The plasma membranes of the oocyte and sperm are fused.

Sperm contents enter oocyte:

The nucleus, mitochondria, and a pair of centrioles enter the oocyte.

Cortical reaction:

The contents of the cortical granules in the oocytee are released into the space between the plasma membrane and the zona pellucida, fusing with the plasma membrane.

This hardens the zona pellucida into a protective envelope, blocking additional sperm from entering.

Without the cortical reaction?

more than one sperm would be able to fuse with the oocyte, a condition known as polyspermy.

If polyspermy did occur, the resulting zygote would not have a diploid (2) genome.

In addition, sperm also donate centrioles, which help form the zygote's mitotic spindle. In polyspermy, extra mitotic spindles are formed, which can lead to aberrant segregation of chromosomes and embryonic death.

Therefore, the cortical reaction aids in fertilization by preventing more than one sperm from entering the oocyte.

The steps of fertilization are as follows:

1. Sperm reaches oocyte

2. Sperm contact

3. Acrosome reaction

4. Fusion

5. Sperm contents enter oocyte

6. Cortical reaction