Gametes in Reproduction (Quiz 1)

Tested in quiz 1 and exam 1. Focuses on the development and fertilization of gametes within sexual reproduction.

Reproduction

A fundamental biological process creating all known life; each individual organism exists as the result of this.

Asexual Reproduction

A uniparental process that does not involve meiosis, s3x organs, fertilization, or zygote formation (rather coming from a single cell or parent part).

More likely to be r-selected, though no variation of progeny is observed.

S3xual Reproduction

A biparental process where meiosis, s3x organs, fertilization, and zygote formation is involved.

More likely to be K-selected, and variation of progeny is widely observed. Evolutionary significance is observed in the population.

Karyotype

An image of a metaphase chromosome complement (the complete set of chromosomes of a eukaryotic organism), arranged according to size and shape.

Genetic Sequence

An inherited DNA sequence.

Epigenetic Sequence

Expression of a DNA sequence. Patterns of chemical marks on the DNA and histones determine which genes should be turned on or off.

PGCs (Primordial Germ Cells)/Gonocytes

Primary undifferentiated stem cell types that will differentiate towards two gametes: spermatozoa or oocytes. Precursors of sperm and egg cells that can pass genetic and epigenetic info onto future generations.

They are embryonic cells, meaning they develop in the embryo.

Germ Cells

A broader category including PGCs and their later differentiated descendants (spermatogonia/oogonia) that actively produce gametes.

Acrosomal Vesicle

A specialized Golgi structure (vesicle) for sperm to bind to and penetrate the egg coat.

Plasma Membrane

A lipid bilayer that protects the entire sperm against oxidative stress.

Mitochondrion in Sperm

Located in the middle piece of the sperm with a spiral shape. Large to power the flagella and make the sperm motile.

Centriole

A modified barrel-shaped organelles at the base of the sperm tail, essential for forming the tail, linking the head to tail, controlling motility, and organizing the first cell division (as a mitotic spindle) after fertilization.

Gametogenesis

The process of differentiation of primordial germ cells into gametes (egg and sperm).

The development of diploid PCGs into haploid eggs or sperm. Includes both spermatogenesis and oogenesis.

Spermatogenesis

The formation of sperm, from PGC to spermatozoa. Occurs throughout adolescence and adulthood. Produced in a continuous, uninterrupted sequence.

Only strongly stimulated when both FSH and androgens from LH are secreted from the pituitary gland.

Mitosis in Spermatogenesis

A spermatogonia cell undergoes this process to develop into a diploid primary spermatocyte.

Meiosis I in Spermatogenesis

Primary spermatocytes undergo this process to develop into haploid secondary spermatocytes.

Meiosis II in Spermatogenesis

Secondary spermatocyte undergo this process to develop into spermatids.

Spermiogenesis in Spermatogenesis

Spermatids undergo this process to develop into spermatozoa.

Zona Pellucida/Jelly Coat

An outer coating of the egg that contains glycoproteins that protect the inner contents of the ovum until the acrosome reaction of fertilization; helps prevent polyspermy.

Corticle Granule

A piece of machinery exclusive to egg cell. Releases enzymes during fertilization that harden the zona pellucida.

Corona Radiata/Follicular Cells

Outermost layer. Protects the inner layers of the ovum and helps prevent polyspermy.

Mitochondrion in Ovum

Several mitochondria that produce ATP. Contains mitochondrial DNA, which is passed to offspring.

Totipotency

The potential to develop into any cell type of the organism. Egg cells are totipotent.

Chemoattractants

Chemical signals released by the egg that can alter sperm swimming direction, where attraction and repulsion is possibly based on choice.

Polyspermy

Multiple sperm being accepted by the egg. Too much genetic info will not develop viable offspring.

Oogenesis

The formation of secondary oocytes and polar bodies from PGCs. Mitotic divisions are complete before birth; production of mature gametes stops around age 50. Process of gamete production has several gaps/interruptions.

Mitosis in Oogenesis

A diploid oogonia cell undergoes this process to develop into a diploid primary/first-degree oocyte.

Meiosis I in Oogenesis

A diploid primary/first-degree oocyte undergoes this process to unequally develop into a large haploid secondary/second-degree oocyte and a small polar body.

Meiosis II in Oogenesis

A secondary/second-degree oocyte undergoes this process to unequally develop into a ovum and a small polar body. Sometimes, the polar body does not apoptose and spilt into two additional polar bodies.

Interspecific Competition

Competition an organism faces against a different species.

Intraspecific Competition

Competition an organism faces against the same species. More severe than interspecific because members of the same species rely on the exact same niche and resources.

Parental Investment Theory

Reproduction is not needed to survive, yet (ex. mammalian) females invest much more energy into developing eggs and carrying young.

Theory suggests that the difference in parental investment is selectively accounted for by behavior from male species to make an environment safer.

Germ Granules

Complexes of RNA and proteins initially distributed throughout the egg but concentrate in the posterior end of the zygote. Suggests that the fate of the cells that will become the germ cells is fixed early in development.

Ex: P granules in C. elegans

Embryo Polarization

The movement of germ granules to the posterior end of zygote before the first cleavage and are found in adult germ cells in the gonad.

Bone Morphogenetic Protein (BMP)

Mammalian protein signaling that activates expression of the transcription factors (initiates specialization) of PCGs by determining their fate and gene expression. Ultimately leads to repression somatic genes and promotion of germ cell specific genes.

Also essential for the formation of organs like the heart, neural system, cartilage, and bones.

Genomic Events

Refers to differential gene expression or cell signaling that happens early in development.

Ex: cell fate (location determination) of P granules in C. elegans, BMP signaling in mammals.

Gastrulation

How cells fold, move, and shift to create structure in a zygote. Overall, organisms become more complex over time (orientation is important).

Proximal Epiblast

Outermost layer of an embryo before it undergoes gastrulation to become primordial germ cells (PGCs) in rodents.

Extra-Embryonic Ectoderm

The outermost tissue on the embryo in rodents.

Migration in the Early Embryo

PGCs divide repeatedly on their migratory route through the gut and into the developing gonads.

SOX9

Rodent transcription factors activated by the activation of the SRY gene.

FGF9

Rodent signaling proteins created by the SOX9 transcription factors.

SRY Gene in Mice Sex Determination

The embryo starts off with low SOX9, RSPO1, WNT4, and FGF9 turned off.

The male SRY gene activates the SOX9 transcription factors to create FGF9 signaling proteins. FGF9 then turns off RSPO1 and WNT4, leading to male development.

Absence of SRY Gene in Mice Sex Determination

The embryo starts off with low SOX9, RSPO, WNT4, and FGF9 turned off.

Without the SRY gene, SOX9 and FGF9 are turned off. RSPO1 proteins and WNT4 proteins remain high, leading to female development.

Bipotential Gonads

An undifferentiated gonad early in development. Capable of becoming ovaries or testes. Implies that all mammals are bipotential at a certain point.

Wolffian Duct

Human male internal genitalia initially present in the undifferentiated gonad.

In masculinization, these structures become the epididymis, vas deferens, and seminal vesicles. The bipotential gonads remain attached.

In feminization, these structures degrade. The bipotential gonads migrate.

Mullerian Ducts

Human female internal genitalia initially present in the undifferentiated gonad.

In feminization, these structures become the uterus, oviducts, and cervix. The bipotential gonads migrate upwards.

In masculinization, these structures degrade. The bipotential gonads remain attached to the Wolffian duct.

Difference Between Female and Male Germ Cell Development

Both germ cells are sexually bipotential during mitosis.

“Male” germ cells are committed to spermatogenesis post-mitosis and pre-meiosis. “Female” germ cells remain sexually bipotential post-mitosis and pre-meiosis while they relocate to the Mullerian ducts.

“Female” germ cells are committed to oogenesis once meiosis-specific transcriptional and epigenetic programs are permanently established. This commitment happens later than males.

Follicle Stimulating Hormone in Females (FSH)

A pituitary gonadotropin hormone that stimulates follicles to grow and mature from a primary oocyte to a secondary oocyte.

Luteinizing Hormone (LH) in Females

A pituitary gonadotropin hormone that triggers ovulation in women.

Germinal Epithelium

A protective cell layer covering the gonads. In females, it acts as the ovarian surface. In males, it serves as tubule lining.

Oogonia

Immature female egg cells that originate from primary germ cells. Produces primary oocytes via mitosis before birth.

Singular: oogonium.

Primary Oocyte

An undeveloped egg cell that arrests in prophase I (after crossing over) after birth and before puberty, residing in a primary follicle. FSH develops them into secondary oocytes.

Secondary Oocyte

The large cell that is unevenly produced by the first division (meiosis I), encapsulated by a secondary follicle and released during ovulation. Progresses to meiosis II but is arrested at metaphase of meiosis II after puberty.

Polar Bodies

Cells produced in the first or second meiotic division in female meiosis that contain little cytoplasm and do not become gametes. They do not have the ability to be fertilized.

Either 2 or 3 polar bodies are produced after oogenesis is complete. It depends on whether or not the polar body is apoptosed before it can divide in meiosis II.

Fertilization

Fusion of haploid sperm nucleus with the haploid egg nucleus.

Ovum

The haploid cell that becomes a functional gamete by completing meiosis II after combining with a sperm cell.

After meiosis II, an additional polar body is produced.

Corpus Luteum

A progesterone-secreting structure that develops in an ovary after an ovum has been discharged but degenerates after a few days if fertilization does not occur.

What is Puberty Triggered By?

Hormones from the hypothalamus and pituitary gland, which will bind to receptors in the testes and ovaries.

Hypothalamus in the Human Female Reproductive Cycle

This structure is inhibited by the combination of high levels of estradiol and progesterone.

It is stimulated by high levels of estradiol and low levels of progesterone. When stimulated, it produces the hormone GnRH.

Anterior Pituitary in the Human Female Reproductive Cycle

This structure is inhibited by low estradiol and is stimulated by the presence of GnRH to release FSH and LH, stimulating the follicle to grow during the follicular phase. A surge in LH triggers ovulation.

Follicular Phase

Estradiol climbs as it is secreted by the growing follicle in increase amounts, which grows the endometrium. A peak in estradiol causes LH to surge.

Luteal Phase

Progesterone and estradiol is secreted by the corpus luteum, both of which promote the thickening of the endometrium.

Cleavage

The rapid series of mitotic cell divisions a zygote undergoes after fertilization without increasing overall size. Each cell is called a blastomere, and they form a hollow sphere called a blastocyst, which then implants into the endometrium.

Theca Cells

The receptor cell for receiving LH, lining the ovarian follicle. These cells produce androgens which are converted to estrogen by the granulosa cell. Vital for triggering ovulation during the mid-cycle LH surge.

Granulose Cells

The receptor cell for receiving FSH, lining the ovarian follicle. These cells produce estrogen and progesterone.

Inhibin in Females

Secreted by the follicular cells of the ovary to inhibit the secretion of follicle stimulating hormone from the anterior pituitary.

Seminiferous Tubules

A network of tubules located in the testes.

Sertoli Cells

Cells that form the walls of seminiferous tubules that weakly promote spermatogenesis or secrete inhibin in response to FSH, maintaining negative feedback in the body.

Leydig Cells

Cells that are adjacent to seminiferous cells, which produce androgens (testosterone) and weakly promotes spermatogenesis.

Seminal Vesicles

A pair of glands which open into the vans deferens to secrete many of the components of semen.

Spermatogonia

Male diploid cells in the gonads that multiply via mitosis and give rise to primary spermatocytes through prophase I of meiosis I.

Primary Spermatocyte

Male diploid cells with replicated chromosomes that continue to complete meiosis I (resulting in haploids).

Secondary Spermatocyte

Male haploid cells that start meiosis II and lead to spermatids.

Spermatids

The four male haploid cells produced by meiotic II division.

Spermatozoa

Structurally mature but immotile sperm cells. Spermatozoa are still interconnected via cytoplasmic bridges to share nutrients via syncytia (allows even development).

Follicle Stimulating Hormone (FSH) in Males

Secreted by the anterior pituitary gland. Stimulates the Sertoli cells.

Inhibin in Males

A peptide hormone secreted by the Sertoli cells of the testis that inhibits secretion FSH from the anterior pituitary.

Luteinizing Hormone (LH) in Males

Secreted by the anterior pituitary gland. Stimulates the Leydig cells to produce androgens, which weakly stimulates spermatogenesis.

GnRH Secretion in Males vs Females

In males, GnRH is secreted in pulses at a constant frequency.

In females, the frequency of the pulses varies during the menstrual cycle, and there is a large surge of GnRH just before ovulation.