DAT Biology: Reproduction and Development Biology

Asexual Reproduction

Organism produces genetically identical offspring

Four Types: binary fission, budding, regeneration + fragmentation, parthenogenesis

Binary Fission

Form of asexual reproduction where DNA replicates, septum forms in the middle, separating the cell

Done by prokaryotes and mitochondria

Budding

Form of asexual reproduction where DNA is replicated and deposited into a bud, which forms a new organism

Done by hydra and yeast

Regeneration

Form of asexual reproduction where a Piece of an organism breaks off, and can regenerate the broken segment

Done by hydra, planaria, fungi

Fragmentation

Form of asexual reproduction where an organism breaks into pieces, and each piece grows into a brand-new, compelte individual

Parthenogenesis

Form of asexual reproduction where unfertilized eggs develop into a viable organism

Done by honeybees which exhibit haplodiploidy (males haploid, females diploid)

Sexual Reproduction

Gametes (male sperm and female egg) combine to form zygotes—genetically distinct offspring

Germ Cells

in males, known as male spermatogonia, and in females, known as female oogonia; specialized biological cell producing gametes via meiosis (can do both mitosis and meiosis)

Spermatogenesis

Formation of haploid spermatoza (sperm cells) from diploid germ cells (spermatogonia)

Spermiogenesis

Final stage in spermatogenesis in which spermatid differentiates into spermatoza

Seminal Vesicles

Secrete fructose (nutrient), viscous mucus (cleans and lubricates urethra), and prostaglandins (stimulate urethral contraction)

Viscous Mucus in Spermatogenesis

Cleans and lubricates urethra

Prostaglandins in Spermatogenesis

Stimulates urethral contraction

Prostate Gland

Alkaline secretions counteract uterine acidity

Bulbourethral Glands

Viscous mucus

Follicle Stimulating Hormone (FSH)

Stimulates sperm production in seminiferous tubules

Stimulates follicles in the ovary to develop

Activates Sertoli cells: nourish sperm cells, produce inhibin (negative feedback on FSH)

Activaes estrogen and progesterone production

Inhibin

Produced by Steroli cells upon activation by FSH, performs negative feedback on FSH

Lutenizing Hormone (LH)

Stimulates Leydig cells to produce testosterone

Stimulates ovulation of egg, corpus luteum formation

Testosterone

Primary male sex hormone responsible for regulating sperm maturation within the seminiferous tubules and driving the development of male secondary sex characteristics (deepening voice, facial hair growth, increased muscle mass)

Ovary

Produces egg cells (ovum, ova)

Fimbriae

Receives eggs released from the ovary

Oviduct/Fallopian Tube

Path between ovaries and uterus that the egg takes, egg has the opportunity to be fertilized here

Uterus

Provides ideal environment for fertilized egg (if fertilized) to implant and develop, having 3 layers:

Perimetrium (outer), Myometrium (middle, muscular), and Endometrium (inner epithelial)

Cervix

Narrow opening between uterus and vagina

Vagina

Opening to external environment, where sperm can enter and birth occurs

Follicle

Fluid-filled sac containing immature eggs (arrested in prophase I) prior to ovulation, upon ovulation, transforms into corpus luteum

Corpus Luteum

Temporary endocrine gland forming in the ovary from an empty follicle after an egg is released during ovulation, secretes progesterone/estrogen to thicken and maintain the uterine lining for potential pregnancy

If fertilization doesn’t occur, it degenerates within about 2 weeks, causing hormone levels to drop and trigger menstruation

Ovulation

A mature egg (oocyte) released from one of the ovarian follicles into the abdominal cavity, swept into the fallopian tube by the fimbriae

Event triggered by a sudden surge in LH and typically occurring around the midpoint of the menstrual cycle (14 of 28-day cycle) marking the fertile window when pregnancy is most likely to occur

Estrogen

Drives female secondary sex traits like breasts, hips, and thickens uterine lining during the first half of the cycle

Progesterone

Released by the corpus luteum after ovulation (day 14), maintains that lining for pregnancy; if fertilization doesn't occur, its drop triggers menstruation.

Lactation

When infants sucking increases prolactin, stimulating milk production (lactation)

Oxytocin is also produced, which releases milk, where milk is let down

Follicular Phase

Estrogen leads to the thickening of the endometrium

Ovulation

Egg is released from the Graafian follicle, and the fimmbriae receive the egg, cilia sweep egg travels through oviduct awaiting fertilization

Luteal Phase

Follicle develops into corpus luteum, which releases progesterone and some estrogen and is maintained by FSH and LH, and estrogen and progesterone exhibit negative feedback on FSH and LH

Implantation

process where a fertilized egg (now called a blastocyst) embeds itself into the thickened, vascular uterine lining (endometrium), typically occurring about 6–10 days after ovulation (around cycle days 20–24). If successful, the embryo releases hCG to rescue the corpus luteum, ensuring it keeps producing progesterone to sustain the lining; if implantation doesn't occur, the corpus luteum degenerates, progesterone plummets, and the lining is shed as menstruation

No Implantation

FSH and LH decrease until the corpus luteum can no longer be maintained

Estrogen and Progesterone drop

Endometrium sloughs off (menstruation), and cycle repeats

Fertilization

Joining of a haploid sperm and haploid egg cell to form a diploid zygote

Capacitation

Final maturation step for sperm prior to encountering the egg, triggered by secretions from the uterine wall

Destabilizes plasma membrane proteins and lipids, preparing sperm tip for acrosomal reaction (meeting egg), and increases calcium permeability resulting in a hyperactive state where the sperm is more active in hopes of meeting an egg cell

Acrosomal Reaction

When the egg and sperm make contact

Corona Radiata

Outermost layer nourishing developing egg in mammalina cells

Vitelline Layer

layer of glycoprotein (jelly coat) above the plasma membrane, known as zona pellucida in mammals

Zona Pellucida

Vitelline layer in mammals, layer of glycoprotein/jelly coat above the plasma membrane

Polyspermy Blocks

Ways to prevent more than one sperm from entering one egg cell

Cleavage

Rapid cell divisions without changing the total mass of cells, to create resulting cells known as blastomeres

3 Types of Cleavage: axis of cleavage, fate of cells, evenness of embryo division

Blastomeres

Cells resulting from rapid cell divisions

Axis of Cleavage

Spiral: cells deviate from the axis (protostomes)

Radial: cells aligned in vertical axis (deuterostomes)

Spiral Axis of Cleavage

cells deviate from the axis (protostomes)

Radial Axis of Cleavage

cells aligned in vertical axis (deuterostomes)

Fate of Cells

Regulative (Indeterminate): blastomeres are totipotent, don’t have pre-determined fate (ex. deuterostomes)

Mosaic (Determinate): blastomeres have a decided fate (ex. protostomes)

Regulative (Indeterminate) Fate of Cells

blastomeres are totipotent, don’t have pre-determined fate (ex. deuterostomes)

Mosaic (Determinate) Fate of Cells

blastomeres have a decided fate (ex. protostomes)

Evenness of Embryo Division

Holoblastic Cleavage: even cleavage, little yolk

Meroblastic Cleavage: uneven cleavage, forms animal and vegetal pole

Meroblastic Cleavage

Performed by egg-laying species (except frogs, which have lots of yolk)

Uneven cleavage, forming an animal pole: high rate of cleavage and little yolk, and vegetal pole: low rate of cleavage, and lots of yolk, source of nutrients for the embryo

Holoblastic Cleavage

Cleavage happens very evenly, very little involvement from yolk, so it ends up dividing pretty evenly

Morola

Solid ball of 16-32 blastomeres, dense, no fluid-filled cavity exists yet

Blastula

Hollow sphere of cells surrounding a central fluid-filled cavity, the blastocoel, marking end of the cleavage stage and establishing the animal-vegetal axis, setting up spatial layout before gastrulation begins

Blastocyst

Mammalian, two cell lineages: inner cell mass (ICM) giving rise tot he embryo proper, and the trophoblast (forming the placenta, surrounding the blastocoel)

Hatches from the zona pellucida around day 5-6 to allow implanation into the uterine endometrium

Gastrula

Triploblastic stage generated by the invagination and movement of cells, prpoducing the 3 primary germ layers: ectoderm, mesoderm, and endoderm.

For DAT, must memorize derivatives: ectoderm gives skin and nverous system, mesoderm gives muscle, bone, and blood, and endoderm gives the gut, lungs, and liver

Stem Cells

Undifferentiated cells with potential to develop in many different ways

Totipotent

Stem cell capable of developing into a complete embryo or differentiationg into any cell type

Pluripotent

Stem cell differentiating into any of the three germ layers

Multipotent

Stem cells differentiating into any cell type with a particular lineage

Differentiated

Differentiated cells are fully specialized and can only reproduce cells of their own type

Neurala

Term for embryo when it develops the nervous system

Stem Cells

Undiffferentiated cells with the potential to develop in many different ways

Notochord

Derived from mesoderm, stimulates ectoderm to thicken into a neural plate

Extraembryonic Development

Structures and development outside of the embryo that provide protection and nourishment to the fetus—most embryos develop into embryotic organisms but some help to support it

Amnion

Innermost layer of the extraembryonic membrane, secreting amniotic fluid to cushion the embryo

Amniotes

Have amnion (reptiles, mammals, birds)

Anamniotes

Lack amnion (amphibians, fish)

Chorion

Outermost layer of the extraembryonic membrane surrounding the developing embryo or fetus

Chorion for Placental Mammals

Forms fetal half of placenta (nutrient exchange)

Chorion for Egg-Laying Mammals

Membrane for gas exchange is underneath the egg shell

Allantois

Sac buds off archenteron, storing waste for disposal

Allantois in Placental Mammals

Transports waste to placenta, forms umbilical cord and eventually urinary bladder in adults

Allantois in Egg-Laying Mammals

Stores uric waste, later fuses with chorion to aid in gas exchange

Yolk Sac in Placental Mammals

Doesn’t contain yolk. Functions temporarily until the placenta forms, providing early nutrients and serving as the first site of blood cell formation

Yolk Sac in Egg-Laying Animals

Contains yolk, supplies all necessary nutrients to the developing of the embryo

Embryonic Induction

Embryo contains cells known as organizer cells, and these organizer cells are going to secrete chemicals that instruct the cell around them on how to differentiate

Homeotic Genes

Determines what part of the embryo will develop into what structures

Master Controller

Turns certain gene expressions on/off

Homebox

A common DNA sequence homologous across different organisms that contain homeotic genes

HOX Genes

Subset of homeotic genes responsible for anterior-posterior (head-tail) organization

Apoptosis

Programmed cell death essential for normal fetal development, as well as health in adults (body modification)

Temperature-Dependent Sex Determination

Some reptiles determine sex by temperature rather than genetics

1. Pattern I: males in cold temp, females in warm temp (turtles)

2. Pattern II: females in low and high temp, males in intermediate temp (crocodiles)

Pattern I

Temperature-Dependent Sex Determination Pattern

Males in cold temps, females in warm temps (like turtles)

Pattern II

Temperature-Dependent Sex Determination Pattern

Females in low and high temperatures, males in intermediate temperatures (like crocodiles)

Oviparity

OFfspring develops in eggs, which hatch outside of the mother’s body

Example: chicken

Viviparity

Offspring develop inside the mother’s body, birth follows

Example: humans

Ovoviviparity

Hybrid between oviparity and viviparity, offspring develops in an egg and hatches within the mother’s body, birth follows

Example: sharks

HOX GEnes

Responsible for development of head to tail