bio 225 exam 3: reproduction

reproduction

* propagation of species: taking one organism and making lots of organisms
* taking DNA in the body and spreading it out
* ultimate end product of life
* maintenance of species

Type main types of reproduction

asexual and sexual

Asexual reproduction

* progeny are genetically identical(or very similar) to their parent
* examples: budding, fragmentation, and parthenogenesis

Budding

ex. Hydras will grow off hydra(look like arms) and break off to fully grow into fully formed Hydra

fragmentation

ex. seastars have many arms, and if one arm happens to break off that has part of the central disc, it can grow into a brand new seastar

Budding, fragmentation

a single individual produces at least one offspring that is genetically identical to the parent

parthenogenesis

asexual reproduction in which an egg develops without fertilization

Ex. of parthenogensis

Komodo dragon: where if there is no presence of males, a female will act as the male and copulate with another female dragon, and as a result, the dragon acting as a female can produce offspring without insemination

Sexual reproduction

* Reproduction of progeny from two parents that contribute to equal amounts of genetic material
* usually: haploid + haploid → diploid

Asexual reproduction vs sexual reproduction

* Easier to make more offspring with less energy with asexual reproduction

Why “choose” sexual reproduction?

* Generates genomic variation at three levels
* Creates population of distinct genotypes

Genomic variation at three levels for sexual reproduction

* Haploid gametes from a diploid parent
* Spermatogenesis in males where testes produce small gametes(sperm)
* Oogenesis in females where ovaries produce large gametes(ova)
* Recombination creates hybrid chromosomes
* Diploid offspring equals unique genetic combinations

Hermaphrodites

* Capacity to produce egg and sperm
* Two different types: simultaneous and serial
* Ex. mollusks, snails, slugs

Simultaneous hermaphrodites

* Produce egg and sperm at the same time

Serial hermaphrodites

* Change in sex in response to environmental cues
* Protogynous and protoandrous

Protgynous

females become males

Protoandrous

males become female

Overview of sexual reproduction

* Life cycle begins with a single cell
* Growth and differentiation
* Reproductive traits established during embryonic development, such as primary sex characteristics with the gonads

Pathway of sexual reproduction

Spermatozoa fertilizes the ovum → becomes a zygote(2-cell stage) → cell division to become a blastula → invaginates to make a gastrula → goes through morphogenesis to become a larva → goes through metamorphosis to become juvenile(nonreproductive) → reproductive development to become an adult(reproductive) → senescence and death to become a post reproductive adult

Zygote

made from fusion of sperm and egg

Blastula

empty ball with cells on the outside

Gastrula

has an internal and external cavity

Some animals are not considered adults until

they can reproduce

Humans and other mammals don’t go through

morphogenesis and metamorphosis, they just become a fetus after the formation of a gastrula

Sex determination by genotype: Mammals

* Presence of a Y chromosome
* Heterogametic male: XY
* Homogametic female: XX

Sex determination by genotype: birds and butterflies

* Heterogametic female: ZW
* Homogametic male: ZZ

Sex determination by genotype: Honeybee(and some ants)

* Fertilized = diploid female
* unfertilized = haploid male

Sex determination by environment

* Example: Temperature dependent sex determination(TSD)

TSD

* Common in reptiles
* Temperature of egg incubation determines sex
* May be due to hormone levels in eggs

Example of TSD

* Sea turtles in Florida use the temperature of their environment to determine their sex ratio
* Alligators nest in rotting vegetation and rotting vegetation gives off heat, so however the female alligator wants to arrange her nest will determine her sex ratio

Trends in sex ratio graph

The warmer it is, the higher the estradiol is going to be, so there will be more females than males in the population

Gametogenesis

production of gametes

Oogenesis

1 Oogonium → 1 primary oocyte → 1 grown primary oocyte → 1 secondary oocyte + first polar body → 1 mature ovum + second polar body

Spermatogenesis

1 Spermatogonium → 1 primary spermatocyte → 2 secondary spermatocytes → 4 spermatids → 4 mature sperm

Meiotic division I

oogenesis: oogonium → primary oocyte → larger primary oocyte

spermatogenesis: spermatogonium → primary spermatocyte

Meiotic division II

oogenesis: secondary oocyte → mature ovum + second polar body

spermatogenesis: secondary spermatocytes → spermatids

Differentiation

spermatogenesis: spermatids → mature sperm

Fate of the Egg: 3 strategies

Ovipary, viviparous, and ovo-vivipary

Ovipary

* ova laid and all development occurs externally
* fertilization can be external or internal
* fish, reptiles, birds

Vivipary

* young develop within the female body
* fertilization internal
* mammals and a few other taxa

ovo-vivipary

* ova “laid” within mothers body
* develops and hatches internally until birth
* sometimes reptiles and fish, plus sharks

platypus

* lay eggs, bill like a duck, and has toxic spores

Reproductive hormones

responsible for: development, sexual maturation, gametogenesis, and mating

ovary and testes are responsible for

develop secondary sexual characteristics and development of sperm or eggs

GnRH

* gonadotropin-releasing hormone
* synthesized and released from hypothalamus
* delivered to anterior pituitary gland
* regulates FSH and LH release

Gonadotropins

* peptide hormones from anterior pituitary
* control steroid hormone synthesis in vertebrates

Types of Gonadotropins

FSH, LH, and chorionic gonadotropin(hCG)

Chorionic gonadotropin

* only in primates
* synthesized by the placenta, which helps tell if you are pregnant

Steroid hormones

* derived from cholesterol
* regulate via gene expression
* bind to a nuclear hormone receptor in target
* vertebrates: produced in gonads
* androgens, ex. testosterone
* estrogens, ex. estradiol

gonads

ovaries and testes

Reproductive steroid hormones

* Progesterone, androstenedione, testosterone, dihydroxytestosterone, estrone, estradiol-17 beta, and 11-ketotestosterone
* all third order hormones

progesterone

* causes thickening of uterine lining which is important for the growth of the fetus
* helps with childbirth

cytochrome P450 aromatase

causes conversion of androgens to estrogens, but not the other way around

dihydroxytestosterone

* implicated in a lot of secondary sex characteristics, like male pattern baldness

Androgens: sexual maturation

* tissue of origin: testes
* main actions: secondary sex characteristics: promote axillary hair growth, voice depending, and libido

GnRH: spermatogenesis

tissue of origin: hypothalamus

main actions: anterior pituitary: stimulates LH release, FSH synthesis and release

LH: spermatogenesis

* Tissue of origin: anterior pituitary
* main actions: leydig cells: stimulates androgen synthesis and release

FSH: spermatogenesis

* tissue of origin: anterior pituitary
* main actions: Sertoli cells: stimulate spermatogenesis

Androgens: spermatogenesis

* tissue of origin: Testes(Lydia cells)
* main actions: Sertoli cells: stimulate spermatogenesis

Prostaglandins

* Tissue of origin: seminal vesicles
* main actions: uterus of mate: induce changes within the uterus that affect sperm motility

negative feedback pathway of inhibin and testosterone

hypothalamus → GnRH → anterior pituitary → FSH and LH → Sertoli cells(FSH) and Leydig cells(LH) → inhibin and spermatogenesis(FSH) and testosterone(LH) → inhibin inhibits the release of FSH, testosterone inhibits FSH and LH

Fertilization

sexual reproduction requires haploid gametes to come in close contact

is a challenge for animals

gametes generally require an aqueous environment and for terrestrial animals this can be difficult

this also leads to fairly high levels of gamete failure

some anatomical and behavioral adaptions have evolved to solve this

External fertilization

most common in aquatic animals

huge gamete numbers are released, even though a large of them don’t survive

egg release and sperm release are synchronized

more cells = more change for successful fertilization

cutthroat trout external fertilization

spawning

internal fertilization

most common in terrestrial animals

avoid gamete desiccation(doesn’t dry out)

provides protection for embryos

usually associated with mating behavior and accessory sex organs

uses copulation

copulation

permits sperm to move directly form male reproductive system to female

human female reproductive organs

follicles/corpus luteum, uterine wall/endometrium, vagina, uterus, cervix, ovaries, oviduct/fallopian tubes

follices

where developing oocyte is

corpus luteum

when the oocyte leaves the ovary

endocrine structure, temporary gland

uterus

location of implantation of a fertilized ovum(egg)

ovaries

production of gametes

oviduct

known as fallopian tubes

where oocyte travels down

site of fertilization

female reproduction and sex cycles

estrous cycle and menstrual cycle

estrous cycle

sexual receptivity coincides with specific phase of cycle

amount of uterine tissue lost is minimal to moderate

present in most mammals - except some primates(chimpanzees and humans)

when fertile females exhibit behavioral cues and pheromones - called “estrus” or “in heat”

usually females are only receptive to copulation during heat

female cats don’t have a

cervical plug, can have multiple fathers in litter

menstrual cycle

sexual receptivity occurs at many phases of the cycle

amount of uterine tissue lost is substantial

present only in some primates(w/ a few other exceptions)

menstrual cycle has 3 phases

1) follicular phase

2) ovulation

3) luteal phase

follicular phase

primary oocyte within follicle → growing follicle → mature follicle

details of follicular phase

estrogen is going up, progesterone is going up, follicle cell is growing through fecal cells, movement from middle to distal ovary

biphasic effect of estrogen

if estrogen is high but not too high, it will inhibit LH and FSH as expected

but if estrogen is way too high, it switches from inhibitory to a stimulating relationship(negative to positive feedback)

peak of estrogen and progesterone around day 14 of cycle

causes ovulation and release of secondary oocyte from follicle, making a ruptured follicle - corpus luteum

luteal phase

corpus luteum allows for secretion of progesterone, which increases the thickening of endometrium to get ready for implantation of fetus

if no fertilization occurs, the corpus luteum degrades because it doesn’t have its own blood supply

endometrium

has a good blood supply, which provides nutrients, glucose, fats, hormones, antibodies etc. to the oocyte

What happens if the corpus luteum starts to degrade?

since the corpus luteum produces progesterone, the progesterone levels will decrease and as a result, the endometrium thickness will decrease and remove all of the unfertilized eggs, causing a menstruation cycle

hCG

made by the placenta, is an LH agonist, and maintains the corpus luteum which produces progesterone to maintain the uterine lining

What do pregnancy tests look for?

Presence of hCG as it is unique to only pregnancy

endometriosis

causes scarring of endometrium, which doesn’t allow for implantation of eggs

treated with birth control

How does birth control simulate the menstruation cycle?

Contains estrogen early in the cycle, pregesterone for 14 days, and last days are a placebo pill to make the body think that it is time to menstruate

Fertilization is

outside the menstruation cycle

Fertilization

when sperm makes it into the oviduct and makes contact with the oocyte

Steps of fertilization

ovulation → fertilization → cleavage for cell duplication → cleavage continues → blastocyst implants into the endometrium

embryonic development

5 days(post fertilization) - inner cell mass, trophoblast, blastocyst

3 weeks → amniotic cavity, embryo

5 weeks → embryo, chorion, allantois, placenta, amniotic cavity

8 weeks → fetus, chorion, allantois, placenta, amniotic cavity

mammalian placenta

interface between mother and fetus, trades nutrients and waste through diffusion

composed of cells derived from both

formation of mammalian placenta

1. outermost cells of blastula differentiate to form trophoblast
2. trophoblast cells invade endometrium, forming an association that will become the placenta

First trimester placenta functions

* has vital endocrine function
* chorion secretes human chorionic gonadotropin(hCG) that causes the corpus luteum to continue secreting estrogen and progesterone

later in pregnancy placenta functions

produces estrogen and progesterone

Parturition(birth) in mammals

induced by contraction of smooth muscle(myometrium) of uterus

begins in response to series of hormonal changes

placenta expelled soon after birth → “afterbirth”

series of hormonal changes during parturition

* progesterone levels decrease allowing uterine muscle to contract
* prostaglandins and oxytocin positive feedback loop induces uterine contractions

Prostaglandins and oxytocin induce uterine contractions

* fetal cells produce oxytocin that causes the placenta to release prostaglandins
* hypothalamic-pituitary axis releases oxytocin

Positive feedback loop with oxytocin and prostaglandins

estradiol from ovaries induces oxytocin receptors on uterus → oxytocin from fetus and mother’s posterior pituitary stimulates uterus to contract + stimulates placenta to make prostaglandins → stimulate more contractions of uterus → contractions stimulate production of more prostaglandins and oxytocin from posterior pituitary