Biology Chapter: Reproduction and Ploidy

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Questions and Answers

What is the chromosomal designation for human gametes?

1n (correct)

How many homologous chromosome pairs do humans normally have?

46 pairs

22 pairs

23 pairs (correct)

24 pairs

What process is required for the formation of gametes?

Meiosis (correct)

Mitosis

Fertilization

Binary fission

Which statement is true regarding the reproductive systems?

They are designed for the union of male and female gametes. Signup and view all the answers

What best describes the ploidy of a normal human cell?

Diploid Signup and view all the answers

What is the purpose of the Dartos muscle in the scrotum?

To regulate the temperature of the testes Signup and view all the answers

What occurs during Meiosis II after fertilization of the secondary oocyte?

The second polar body is extruded Signup and view all the answers

Which structure is primarily responsible for sperm delivery to the female reproductive tract?

Penis Signup and view all the answers

What role do the cremaster muscles play in the male reproductive system?

Elevating the testes Signup and view all the answers

What is the optimal temperature for sperm development in the testes?

34°C Signup and view all the answers

Which male reproductive structure is responsible for sperm maturation?

Epididymis Signup and view all the answers

Which of the following structures helps in maintaining a lower temperature for optimal sperm development?

Cremaster muscle Signup and view all the answers

What does the scrotum consist of?

A sac of skin housing the testes Signup and view all the answers

What is the main function of the male reproductive system?

Production of sperm and delivery to the female Signup and view all the answers

What is the purpose of the midline septum in the scrotum?

To divide the scrotum into compartments for each testis Signup and view all the answers

What is the primary function of meiosis?

To produce haploid gametes Signup and view all the answers

During which phase do homologous pairs form tetrads?

Prophase I Signup and view all the answers

What is the end result of meiosis II?

Four haploid cells Signup and view all the answers

What is the role of Type A spermatogonia in spermatogenesis?

To maintain germ cells and produce more spermatogonia Signup and view all the answers

Which process occurs immediately before meiosis begins in spermatogenesis?

DNA replication Signup and view all the answers

What do spermatids undergo during spermiogenesis?

Transformation into a motile spermatozoon Signup and view all the answers

What triggers the resumption of meiosis I in oogenesis?

Hormonal changes at puberty Signup and view all the answers

What is produced along with a secondary oocyte after the first meiotic division?

One polar body Signup and view all the answers

How long does a full cycle of spermatogenesis take?

74 days Signup and view all the answers

What is the main purpose of the acrosome in a spermatozoon?

Aid in penetrating the ovum Signup and view all the answers

What occurs to some primary oocytes before they resume meiosis?

They undergo apoptosis Signup and view all the answers

What happens to the germ cells as they move towards the lumen in the seminiferous epithelium?

They become older and more mature Signup and view all the answers

What occurs during the late stage of spermatogenesis called spermiogenesis?

Repackaging of DNA in spermatids Signup and view all the answers

What is the primary function of the corpus spongiosum?

Surrounds the urethra Signup and view all the answers

Which cells are responsible for the production of testosterone?

Leydig cells Signup and view all the answers

What is the main function of the Sertoli cells?

Provide nutrients for maturing sperm Signup and view all the answers

What role does the epididymis play in sperm development?

Stores sperm temporarily Signup and view all the answers

Which substance found in seminal fluid helps neutralize the acidity of the urethra?

Mucus-like secretions Signup and view all the answers

What percentage of seminal plasma is produced by the prostate gland?

35-45% Signup and view all the answers

How does the alkalinity of semen contribute to sperm survival?

It neutralizes vaginal acidity Signup and view all the answers

What is the function of myoid cells surrounding the seminiferous tubules?

Contract rhythmically to move fluids Signup and view all the answers

What process occurs in the seminal vesicles?

Secretion of fluid that dilutes sperm Signup and view all the answers

Which hormone is crucial for stimulating the production of testosterone?

LH Signup and view all the answers

What is one of the main roles of the ejaculatory duct?

Carries sperm to the urethra Signup and view all the answers

What percentage of seminal plasma is secreted by the bulbourethral glands?

5-15% Signup and view all the answers

Which characteristic defines the structure of semen?

Milky-white and sticky Signup and view all the answers

What is one function of prostaglandins in semen?

Induce smooth muscle contraction Signup and view all the answers

Study Notes

Overview of Reproduction

Reproduction depends on the union of male and female haploid gametes to create a diploid individual with a unique chromosome set.
Reproductive systems are designed to enable the union of genetic material from two partners (male + female).
The female reproductive system is designed to nurture the offspring until it can survive independently in the external environment.
The reproductive system includes the gonads, reproductive tract, and accessory sex glands.

Significance of Ploidy

All normal humans have two sets of chromosomes (one from each parent).
This pairing is called the diploid chromosomal number (2n).
Humans have 23 pairs of homologous chromosomes (46 total), with 23 chromosomes from each parent.
Homologous chromosomes carry genes for the same traits.
Gametes (sperm and egg) are haploid (1n), containing 23 chromosomes.
Gamete formation is a unique process called meiosis.

Mitosis vs Meiosis

Mitosis: A single cell division resulting in two identical daughter cells. Original cells have diploid number of chromosomes (2n), resulting in 2 diploid daughter cells.
Meiosis: A two-stage cell division process resulting in four unique haploid cells. The original diploid cell (2n) gives rise to 4 haploid daughter cells.

Meiosis

Prophase I: Synapsis of homologous chromosomes to form tetrads, crossing over can occur.
Metaphase I: Tetrads align on the metaphase plate.
Anaphase I: Homologous chromosomes separate.
Telophase I: Sister chromatids remain together, and the cell divides, creating two haploid daughter cells.
Prophase II: Chromosomes condense.
Metaphase II: Chromosomes align on the metaphase plate.
Anaphase II: Sister chromatids separate.
Telophase II: Four haploid daughter cells are formed.

Spermatogenesis

Mitotic proliferation: Maintaining germ cells and increasing their numbers.
Type A spermatogonia: Divide to ensure a continuous supply of germ cells, differentiating into Type B spermatogonia.
Type B spermatogonia: Destined to become spermatozoa, undergoing mitotic divisions to produce primary spermatocytes.
Meiosis (early spermatogenesis): Producing haploid gametes. Primary spermatocytes replicate DNA before the first meiotic division, producing secondary spermatocytes. Then, via a second division, produce 4 haploid spermatids.
Spermiogenesis (late spermatogenesis): Remodels spermatids into mature spermatozoa. DNA is repackaged and organelles are lost or remodeled.

Spermiogenesis

The transformation of spermatids into sperm (spermatozoa).
Involves several stages: acrosome formation, reorganization of organelles, DNA condensation and removal of excess cytoplasm.

The Spermatozoon

A specialized haploid cell resulting from spermatogenesis.
Four major parts: Head (repackaged DNA), acrosome (enzymes to penetrate the ovum), midpiece (mitochondria for energy), and tail (flagella for sperm movement).

Seminiferous Epithelial Cycle

A full cycle of spermatogenesis, typically taking ~74 days, involves a pattern of germ cells moving from the basal membrane to the lumen of the seminiferous tubule.
Cells become more mature as they approach the lumen.
A new cycle begins every ~16 days.

Oogenesis

Occurs in the ovaries.
Begins with mitotic division and meiotic arrest in the fetal ovary.
A pool of oogonia (~6-7x10⁶) develop mitotically.
Oogonia enter meiosis I, forming primary oocytes, which arrest in prophase I before birth, and remain until puberty.
During puberty, some primary oocytes resume meiosis I.
Meiosis I results in one secondary oocyte and one polar body.
In meiosis II, a secondary oocyte begins, but only completes meiosis II if fertilization occurs (resulting in an ovum).
Polar bodies degenerate.

Resumption of Meiosis

Puberty to menopause: A portion of the resting pool of primary follicles are induced to resume meiosis I.
Primary oocyte undergoes the first meiotic division, producing a secondary oocyte and a polar body.
The secondary oocyte dominates and other oocytes undergo atresia.

Male Reproductive System

Function: Production of sperm (spermatogenesis) and delivery of sperm to the female.
Structures: Testes, epididymis, vas deferens, seminal vesicles, prostate gland, bulbourethral glands, urethra.

The Scrotum

Skin sac containing the testes and epididymis.
Divided by a midline septum to create compartments for each testis. This allows for temperature regulation for optimal sperm production (~34°C).
External raphe marks the division.
Cremaster and dartos muscles adjust the position of the testes to maintain temperature.

The Penis

Copulatory organ for sperm delivery.
Composed of erectile tissue (vascular spaces) that engorge with blood during arousal, causing the penis to enlarge and become rigid.
Two corpora cavernosa and one corpus spongiosum.

The Testes

Site of spermatogenesis.
Covered by tunica albuginea and tunica vaginalis.
Septa divide the testes into lobules containing seminiferous tubules.
Myoid cells surround the seminiferous tubules, possibly helping to propel sperm.
Rete testis connects the seminiferous tubules to the epididymis.

Sertoli Cells

Line the seminiferous tubules and support spermatogenesis.
Provide nutrients and support for maturing germ cells and produce androgens-binding protein (ABP).
Involved in the blood-testis barrier.
Phagocytic, removing cellular debris.

Leydig Cells

Located in the interstitial tissue of the testes.
Produce testosterone in response to LH from the anterior pituitary.

The Ducts (Epididymis)

Sperm move through the epididymis over ~20 days.
Three different regions, playing roles in modifying sperm motility, metabolism, and morphology.
"Finishing school" to prepare sperm for fertilization (includes secretion of fluid and concentration/storage of sperm.)

The Other Ducts (Vas Deferens, Ejaculatory Duct)

Ductus deferens: Transports sperm from the epididymis, through the spermatic cord (a group of blood vessels and nerves that connect the epididymis to the body ) and to the seminal vesicle. Muscular layers propel sperm via peristalsis. Storage site for sperm.
Ejaculatory duct: Juncture between seminal vesicle and vas deferens. Short duct that empties into the urethra.

Seminal Vesicles

Paired structures located posterior to the bladder.
Merges with the ductus deferens to form the ejaculatory duct.
Secretes ~50% of seminal plasma (fluid containing fructose, aiding sperms' motility., and prostaglandins that stimulate muscle contractions).

Prostate Gland

Located immediately inferior to the bladder.
Encircles the urethra.
Secretes ~35-45% of seminal plasma (including slightly acidic secretions containing citric acid and antibiotic, prostastic fluid).

Bulbourethral Glands

Also called Cowper's glands.
Located within the urogenital diaphragm.
Paired structures.
Ducts travel to the spongy urethra, secreting mucus-like substance (5-15% of seminal plasma) acting as lubrication to the urethra prior to ejaculation.

Semen

Mixture of seminal plasma and sperm.
Created during ejaculation.
Characteristics: milky-white, sticky, 3-5 mL volume, alkaline, contains ~200-500 million sperm.

Semen Function

Sperm survival: Alkaline environment, clotting factors.
Sperm movement: Liquefaction, prostaglandins, helping sperm motility and penetration
Suppressing the female immune response: Substances prevent bacterial expansion
Protecting the sperm: Some ejaculate components are antibacterial.

Hormonal Regulation of Testicular Function

Complex interplay of hormones (GnRH, LH, FSH, inhibin, testosterone, and estrogen).
Hypothalamus and anterior pituitary regulate testicular (androgen) function.
Includes feedback mechanisms.

Function of Testosterone

Pre-partum: Masculinization of reproductive tract and external genitalia, promotes descent of testes.
Post-partum: Essential for spermatogenesis, promoting reproductive system growth and maturation, maintenance of reproductive tract in adulthood, and development of secondary sexual characteristics (hair growth, larynx deepening, muscle growth).

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Description

Explore the intricacies of reproduction, including the roles of male and female gametes and the significance of ploidy levels in humans. This quiz covers the female reproductive system, the diploid chromosomal number, and the processes of mitosis and meiosis. Test your understanding of these essential biological concepts.