BIOL 216 - Topic 1

Reproduction

the biological process by which new individual organisms (or offspring) are produced from their "parents", fundamental feature of all known life, each individual organism exists as the result of reproduction

Sexual reproduction

typically requires the involvement of two individuals or gametes one each from opposite type of sex

Primordial germ cell

early embryonic cells that acquire the developmental potential to develop into the gametes

Oogenesis

egg development

Spermatogenesis

sperm development

Characteristics of egg cells

large, non-motile, abundant raw materials and machinery, yolk is the energy supply, totipotent, unique haploid genome, egg coat, cortical granules

Totipotent

developmental potential to develop into any cell type of the organism

Egg coat

outer protective coat, shell jelly coat

Cortical granules

specialized golgi structures that protect an egg against polyspermy

Functions of the egg

contributes ½ of the unique diploid genome, provides mechanism for sperm recognition, binding, fusion, and prevention of polyspermy

Characteristics of sperm cells

unique haploid genome, small, motile with flagella, few organelles (mitochondria, centrioles), acrosomal vesicle

Acrosomal vesicle

specialized golgi structure used by the sperm to bind to and penetrate the egg coat

Functions of the sperm

get to and fuse with the egg, contribute ½ of the genome, activate the egg

Gametogenesis

the development of diploid cells (PGCs) into either haploid eggs or sperm

PGCs

precursor germ cells (aka gonocytes) are primordial germ cells that still have to reach the gonads, divide repeatedly on their migratory route through the gut and into the developing gonads

Wolffian duct

male internal genitalia such as epididymis, vas deferens, and seminal vesicles

Mullerian duct

female internal genitalia such as the uterus, oviducts, and cervix

Which type of germ cell commits to their path first?

male germ cells

Purpose of mitosis in the process of gametogenesis

expansion of the primordial germ cell population

Purpose of meiosis during gametogenesis

development of diploid germ cells into either haploid eggs or sperm for sexual reproduction

Asexual reproduction

offspring arise from a single parent, primary form of reproduction for single-celled organisms such as the archaea, bacteria, and protists

Steps of cell cycle

G1 (growth and normal metabolic roles), S (DNA replication), G2 (growth and preparation for mitosis), M (mitotic phase), first three form interphase

Mitosis

occurs in somatic cells, chromosomal number is not halved

Meiosis

process by which the number of chromosomes in a cell nucleus is halved during the formation of germ cells, one way process that won't engage in the cell cycle like mitosis

Stages of mitotic cell division in an animal cell

G2 of interphase, prophase, prometaphase, metaphase, anaphase, telophase and cytokinesis

G2 of Interphase

chromatin is duplicated, nuclear envelope intact

Prophase

chromatin condenses into chromosomes composed of two sister chromatids apiece, early mitotic spindle forms

Prometaphase

nuclear envelope dissolves, centrosomes move to the spindle pole position, chromosomes attached to mitotic spindle at the kinetochore

Metaphase

chromosomes arranged at the metaphase plate

Anaphase

centromeres retract mitotic spindle fibers to pull sister chromatids apart towards their respective sides of the cell

Telophase and cytokinesis

nucleolus, the nuclear envelope, and the cleavage furrow begin forming

Nucleolus

transcribes ribosomal RNA

Stages of meiosis

interphase, prophase 1, metaphase 1, anaphase 1, telophase 1 and cytokinesis, prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis

Interphase

chromosomes duplicate, nuclear envelope intact, chromatin

Prophase 1

homologous chromosomes pair and exchange segments, nuclear envelope dissolves, tetrads form chiasmata to allow for crossing over, spindles begin to form

Metaphase 1

tetrads line up along metaphase plate, microtubule attaches to kinetochore

Anaphase 1

pairs of homologous chromosomes split up, sister chromatids remain attached to the spindles

Telophase 1 and cytokinesis

two haploid cells form with two chromosomes made up of two sister chromatids each in each daughter cell, cleavage furrow begins to form

Prophase 2, metaphase 2, anaphase 2, telophase 2 and cytokinesis

same division steps as mitosis occur to result in four haploid daughter cells containing single chromosomes

Methods of producing offspring of varied genotypes

meiotic recombination and fertilization

Two ways in which variation is generated during meiosis

chromosome segregation (independent assortment) and crossing over (homologous recombination)

Number of new chromosome combinations produced by meiosis is

2^n where n= number of haploid chromosomes (humans=23) and 2= number of chromosomes in each pair

Chromosomes

structures that contain DNA

Levels of DNA condensation

DNA double helix, histone proteins, nucleosome, supercoil, chromatids

Gene

stretch of DNA that codes for something, made of exons and introns

Oogonia

produced by primary germ cells, then they reproduce by mitosis to produce primary oocytes, mitotically active cells that produce primary oocytes

Primary oocytes

begin meiosis then arrest at prophase 1, these are present in females at birth and reside in a follicle

Follicle

cavity lined with cells, at puberty FSH stimulates them to grow and mature with one usually fully maturing per month after which the oocyte completes meiosis 1

Mitosis

occurs in somatic cells, chromosomal number isn't halved

Meiosis

process by which the number of chromosomes in a cell nucleus is halved during the formation of germ cells (eggs and sperm)

In which two ways is variation produced during meiosis?

chromosome segregation (independent assortment) and crossing over (homologous recombination that occurs during Prophase 1 of Meiosis 1)

Chromosomes

structure that contain DNA

Primary germ cells produce

oogonia

Oogonia reproduce by mitosis to produce

primary oocytes

Primary oocytes begin meiosis then arrest at

prophase 1

Primary oocytes reside in

a follicle

Follicle

cavity lined with cells

At puberty ___ stimulates follicles to grow and mature

FSH

Cytokinesis of meiosis 1 is uneven resulting in one small cell _____ and one large cell ____

the first polar body and the secondary oocyte

The secondary oocyte progresses to meiosis 2 but is stopped at

metaphase 2 of meiosis 2

Ovulation

breaking open of the follicle to release the secondary oocyte occurs

When does meiosis 2 resume?

when a sperm penetrates the secondary oocyte

Fertilization

fusion of haploid sperm nucleus with haploid egg nucleus

Corpus luteum

forms from the ruptured follicle, produces progesterone (thickens uterus lining for pregnancy), degenerates if fertilization doesn't occur

Spermatogenesis

continuous process in adult males, hundreds of millions of sperm produced each day,

Maturation time for a single sperm

7 weeks

Testes

develop in the abdomen and descend into the scrotum

Seminiferous tubules

network of tubules located in testes

Sertoli cells

form the walls of seminiferous tubules and support germ cells

Leydig cells

adjacent to seminiferous tubules, produce androgens such as testosterone

Testicular spermatozoa are immature and cannot penetrate the egg so they move from the testes to the ___ where they mature

epididymis

During ejaculation sperm move from the ____ to the ______ to the _______ where they mix with _____ from the _____ and _______

epididymis, vas deferens, ejaculatory duct, seminal fluid, prostate, seminal vesicles

Sertoli cells

provide nutrients during differentiation

Terminology of the sperm as it's created

primordial germ cell, mitosis, spermatogonial stem cell, mitosis, spermatogonium, mitosis, primary spermatocyte, meiosis 1 (now is n), secondary spermatocyte, meiosis 2, early spermatid, differentiation, sperm cell

Acrosome

vesicle with enzymes that facilitate egg penetration

Mitochondria

provide ATP for tail movement/swimming

Hormonal control route of the testes

hypothalamus gives GnRH to the anterior pituitary gland, the gland gives FSH to the sertoli cells and LH to the leydig cells, the sertoli cells help spermatogenesis and make inhibin which inhibits the anterior pituitary, the leydig cells produce testosterone which helps spermatogenesis and negatively feedbacks the anterior pituitary and hypothalamus

FSH

follicle stimulating hormone

LH

luteinizing hormone

GnRH

gonadotropin releasing hormone

Terminology of the egg as it's created

primordial germ cell, mitosis, oogonium, mitosis, primary oocyte (present at birth stuck in prophase of meiosis 1), follicle matures, completion of meiosis 1 and onset of meiosis 2, secondary oocyte (stuck at metaphase of meiosis 2), ovulation, if sperm enters meiosis 2 is completed and the final fertilized egg is made

Ovarian cycle phases

follicular phase, ovulation, luteal phase

Follicular phase

days 0-7 growing follicle, days 7-14 maturing follicle, increasing levels of FSH and LH, increasing levels of estradiol and progesterone

Ovulation

days 14-15 opening of the follicle, triggered by LH surge, quickly increasing amount of FSH, steep drop in estradiol, increasing amounts of progesterone

Luteal phase

days 15-23 corpus luteum is formed, days 23-28 the corpus luteum degenerates, LH and FSH steadily decrease, around day 20 there is a steep surge in progesterone and estradiol and then they steadily decrease

Uterine cycle phases

menstrual flow phase, proliferative phase, secretory phase

Menstrual flow phase

days 0-5, steep decline in the thickness of the endometrium

Proliferative phase

days 5-14 steady increase in the thickness of the endometrium

Secretory phase

days 14-28 further increase in the thickness of the endometrium, thickest point at day 25 and then a small decline after that

What ovarian hormones promote the thickening of the endometrium

progesterone and estradiol

What hormone is at a very low level during the menstrual flow cycle

estradiol

Phases of zygote formation and early development

ovulation, fertilization, cleavage (24hr pc), cleavage continues (2-3d pc, 16 cell embryo enters the uterus), implantation (7d pc, blastocyst implants in the endometrium)

Trophoblast

outer layer of the blastocyst, helps form the placenta

Inhibin

a peptide hormone secreted by the follicular cells of the ovary and the sertoli cells of the testis that inhibits secretion of FSH from the anterior pituitary

Differences between spermatogenesis and oogenesis number 1

S: all four products become gametes, O: one product of meiosis becomes the egg and the other two become polar bodies that eventually degenerate

Differences between spermatogenesis and oogenesis number 2

S: occurs throughout adolescence and adulthood, O: mitotic divisions are complete before birth and production of mature gametes stops around age 50

Differences between spermatogenesis and oogenesis number 3: S: sperm are produced from gametes in a continuous sequence (mature sperm zygote total time 48 days), O: process of gamete production has gaps/interruptions (mature egg zygote total time 12-50 years)

Spermatogonia

mitotically active cells in the gonads that give rise to spermatocytes

Spermatids

the four haploid cells produced by meiotic division of a primary spermatocyte

Polar body

small haploid cell formed from uneven division during cytokinesis during meiosis in oogenesis, only two are produced, usually apoptose and disappear