Reproduction

  • reproduction - production of offspring

    • sexual

      • merging of haploid gametes from 2 distinct individuals

      • produces new allele combos

      • diversity + adaptation

      • driven by environmental change

    • asexual

      • produces genetically identical offspring

      • involves only 1 parent

      • optimized for stable, existing conditions

  • meiosis - produces haploid eggs + sperm

    • sexual reproduction

    • maintains diploid number of chromosomes

      • fusion of egg + sperm → diploid zygote

    • creates genetic diversity

      • crossing over

      • independent assortment

      • fertilization of gametes = random

  • Sperm and Egg

    • both are gametes

      • fuse to form zygotes

    • egg size > sperm size

    • sperm

      • 0.005 mmm

      • produced in testes

      • millions released per ejaculation

      • motile - swim to egg

      • continuous production

        • billions in lifetime

      • X or Y chromosome

    • egg

      • 0.1 mm

      • produced in ovaries

      • 1 egg released per month

      • contains cytoplasm + nutrients

      • limited supply

        • 400-500 per lifetime

      • X chromosome only

  • Male reproductive system

  • Scrotum

    • sack enclosing balls/testis

    • keeps at correct temperature

  • Testis

    • makes sperm/spermatogonia + testosterone

  • Epididymis

    • stores sperm

  • vas deferens

    • moves sperm from epididymis → urethra

  • cowper’s gland

    • makes lubrication for urethra before ejaculation

  • seminal vesicle

    • makes fluid for semen (70%)

    • nurtures sperm

      • fructose

  • prostate gland

    • 30% of semen

    • alkaline

  • urethra

    • carries sperm + urine

  • penis

    • male organ inserted into vagina

  • Female reproductive system

  • ovary

    • make + store + release eggs into fallopian tubes

      • during ovulation

  • oviduct/fallopian tube

    • 2 tubes linking uterus to ovaries

    • where fertilization occurs

    • fimbrae - projections at the ends of fallopian tubes closest to ovaries

      • catch egg that ovaries release → sweep into fallopian tube

  • uterus

    • organ where baby grows during pregnancy

    • made of muscles

  • cervix

    • where vagina + uterus join

    • widens during birth to let baby pass

  • vagina

    • hollow tube linking uterus to outside body

    • menstrual blood + baby exits

    • penis inserted during sex

  • labia

    • inner + outer

      • outer covered in pubic hair

    • skin flaps that surround vagina + urethra

  • clitoris

    • small sensory organ w nerve endings

    • causes pleasure during sex

  • endometrium

    • inner lining of uterus

    • sheds during period

    • where embryo implants

  • myometrium

    • muscular layer

    • contracts during period + birth + orgasm

  • perimetrium

    • protective tissue layer

    • keeps uterus intact

  • spermatogenesis - production of spermatozoa (sperm)

    • epididymis - site of maturation

    • seminiferous tubules - site of spermatogenesis

      • epithelial (germ) cells give rise to spermatogonia

        • near outer wall of tubules

      • cells undergo mitosis/meiosis → cells migrate to Lumen

      • cells nourished by sertoli cells (supporting cells)

        • sertoli cells get signals from pituitary gland via FSH

          • triggers meiosis I + supports spermatogenesis

    • Leydig cells - produce testosterone

      • clustered outside tubules

      • have receptors for pituitary hormone LH

      • drive meiosis II + differentiation into mature sperm

    • Sperm production

      • Step 1

        • (diploid) spermatogonia undergo mitosis + growth → primary spermatocyte

      • Step 2

        • (diploid) primary spermatocyte undergoes meiosis I → 2 secondary spermatocyte

      • Step 3

        • (haploid) secondary spermatocyte undergo meiosis II → each produces 2 spermatids

      • Step 4

        • (haploid) spermatids undergo differentiation → sperm

      • After spermatogenesis → sperm go to epidiymis
            gain motility + storage

  • oogenesis - production of ova (eggs)

    • initial steps begin when female is a fetus

      • oogonia - stem cells for egg formation

        • no longer exists at birth

    • puberty - FSH promotes growth of follicle cells + drives primary oocyte to continue process of meiosis

    • Ova production

      • step 1

        • fetal development

        • (diploid) oogonia formed

      • step 2

        • (diploid) oogonia undergoes mitosis + growth → primary oocyte

        • mitotic arrest at P1 (pause)

      • Step 3

        • FSH → puberty

        • (diploid) primary oocyte undergoes meiosis I → 1 polar body + 1 (haploid) secondary oocyte

          • corona radiata - follicle cell that stays with secondary oocyte

      • Step 4

        • LH → ovulation - process where secondary oocytes erupt from the ovary

          • corpus luteum formed from remaining follicle cells

        • (haploid) secondary oocyte undergoes meiosis II → 1 polar body + (haploid) ovum

        • final products (per primary oocyte): ovum + 3 polar bodies

  • Oogenesis and spermatogenesis

    • BOTH

      • growth + mitosis

      • 2 series of meiosis

      • reduction in chromosome number to haploid

      • differentiation

      • regulation via hormones

    • OOGENESIS

      • unequal division of cytoplasm

      • 1 ovum + polar bodies

      • pauses

        • Prophase 1 + metaphase II

      • polar bodies exist

      • release 1 secondary oocyte a month

      • location in ovary

      • begins during embryonic development

      • stops during menopause

    • Spermatogenesis

      • equal division of cytoplasm

      • 4 sperm

      • no pauses

      • no polar bodies

      • many/frequent releasees

      • location in testes

      • begins during puberty

      • stops at death

  • Sperm

    • small + streamlined shape

      • adapted to swimming

  • Haploid nucleus

    • in head of sperm

    • contains paternal genetic info

  • acrosome

    • in head of sperm

    • hydrolytic enzymes

      • aid in fertilization

  • midpiece

    • contains mitochondria → ATP to swim

  • flagellum

    • sperm can swim + reach egg

  • Ova

    • large cells

    • contain haploid nucleus

  • zona pellucida

    • prevents polyspermy

  • cortical granules

    • vesicles

    • make zona pellucida impenetrable to sperm after fertilization

  • lipid droplets

    • in cytoplasm

    • provide developing embryo w energy

  • corona radiata

    • layer of follicle cells on very outside

    • gives vital proteins to the cell + shields egg from environmental damage

  • hormones + puberty

    • childhood - secretion of FSH + LH inihibted by low levels of gonadotropin releasing hormone

      • FSH - follicle stimulating hormone

      • LH - luteinizing hormone

    • certain stage of development during childhood

      • hypothalamus increases secretion of GnRH → increase in FSH and LH

      • males

        • LH → testosterone

        • FSH → sperm

      • females

        • FSH + LSH FSH + LH regulate menstrual cycle + production of oestradiol/progesterone

    • sex hormones → secondary sex characeristics

      • girls

        • breasts

        • bigger hips

        • pubic/armpit hair

      • boys

        • deeper voice

        • facial hair

        • more muscle

  • menstrual cycle

    • menstruation (0-5)

      • all hormones low

      • low P + oestradiol at very beginning → endometrium shed

      • FSH increases

      • some ovarian follicles start growing

      • near end → oestradiol (oestrogen) starts to increase

    • days 5-14

      • dominant follicle emerges → oestradiol produced

      • oestradiol → thickens uterine lining

      • oestradiol negative feedback FSH

        • aka decrease in FSH

    • ovulation (day 14)

      • oestradiol peak → slight positive feedback to release LH (pituitary)

        • LH peak

          • follicle ruptures → mature egg released

      • matures secondary oocyte + triggers ovulation/formation of corpus luteum

      • FSH short peak

    • Days 14-28

      • ruptured follicle → turned into corpus luteum

        • filled with cells

      • corpus luteum (ovary) secretes Progesterone + some oestradiol

      • Progesterone thickens + vascularizes + matures endometrium

      • low LH + FSH

      • progesterone peak

  • feedback loops

    • Days 12-14

      • more oestradiol → more LH/FSH from pituitary → more GnRH from hypothalamus

        • positive

    • Over most of cycle

      • more orestradial → less LH/FSH from pituitary → less GnRH from hypothalamus

  • Fertilization - fusion of egg + sperm

    • occurs in oviduct/fallopian tubes

    • sperm tail detaches + mitochondria destroyed

      • enters egg

    • nuclear membrane of sperm + egg break down → chromosomes from both condense → meiosis

    • Steps

      • sperm attracted by chemicals released in oocyte → swim toward it

      • first sperm breaks through corona radiata → binds to proteins in zona pellucida

      • binding → acrosome reaction → acrosome enzymes released

      • enzymes digest route to plasma membrane of oocyte

      • plasma membrane of oocyte + sperm fuse → nucleus of sperm enters oocyte → tail/mitochondria of sperm break

      • meiosis II completed in ovum

      • cortical reaction → cortical granules move toward the plasma membrane of ovum → release enzymes into zona pellucida

      • enzymes from cortical granules → cross linking of glycoproteins in zona pellucida

        • prevents polyspermy

  • IVF (in vitro fertilization) - fertilization occurs outside female body (in vitro = in glass)

    • first IVF baby = Louise Brown

    • Steps

      • normal menstrual cycle halted via oestriadol

      • high doses FSH injected to stimulate follicle development

        • superovulation - up to 20 oocytes can develop

      • human chorionic gonadotropin (hCG) injected into woman → stimulates oocytes to mature

        • mimics LH role

      • secondary oocytes harvested + sperm collected from male (sperm screened for health)

      • 2 ways for fertilization

        • oocytes mixed w up to 100k sperm at 37C

        • single sperm is injected directly into egg

      • fertilized egg → zygote → divides via mitosis → up to blastocyst

      • 1+ embryos placed into uterus after 2-5 days

        • screening maybe

      • extra progesterone inserted into vagina → maintains endometrium

      • pregnancy continues as normal

  • the zygote

    • product of fertilization

    • carries out mitosis + cytokininesis → 2 cell embryo

    • continues to divide → morula

      • morula - hollow ball of identical cells

    • morula begins to differentiate → blastocyst

      • blastocyst - hollow ball of cells w inner cell mass (embryo)

      • outer cells = placenta

      • formed around day 5

      • around 125 cells

        • embryonic layer = inner

        • trophoblast = pre-placental layers

    • Day 7-8 → blastocyst implants into endometrium

  • Blastocyst

    • outer layer develops finger-like projections → penetrate uterine lining

      • implantation

      • allows exchange of materials btwn parent and embryo

  • human chorionic gonadotropin (hCG) - released by embryo + developing placenta

    • maintains corpus luteum

      • ensures uterine lining does not break down

    • stimulates ovary to secrete progesterone in early pregnancy

      • embryo secrets hCG → replaces role of LH in maintianing corpus luteum → allows progesterone to be secreted to maintain endometrium

  • pregnancy tests

    • use monoclonal antibodies → bind to human chorionic gonadotropin

      • monoclonal antibodies - antibodies produced by a single cell line

        • all identical

      • hCG = antigen for monoclonal antibodies

  • 8 weeks of development → embryo gets bone tissue → foetus

    • foetus connects to placenta via umbilical cord

  • placenta - disc shaped structure with many projections (villi)

    • embedded in endometrium

    • maternal blood pools via open ended arterioles into intervillous spaces

      • placental (chorionic) villi extends to these spaces → large surface area for exchange of materials

  • Materials exchanged

    • foetus → adult (umbilical artery)

      • CO2 + Urea

        • diffusion

          • CO2 along conc gradients

      • water

      • hormones

        • ex. hCG

    • adult → foetus (umbilical vein)

      • O2

        • diffusion along conc. gradients

      • nutrients, vitamins, minerls

        • facilitated diffusion + active transport

      • water

      • hormones

      • antibodies

        • endocytosis

      • alcohol, drugs, nicotine

      • viruses

  • placenta secretes hormones → maintain pregnancy

    • oestradiol + progesterone + hCG

    • allows human foetus to be retained in uterus until later stage of development than mammals that dont get placentas

  • hormones maintaining pregnancy

    • progesterone + oestradiol

      • secreted by corpus luteum early in pregnancy

        • maintain uterine lining

      • later secreted by placenta to maintain pregnancy

    • hCG

      • maintains corpus luteum

  • childbirth regulated by interactions btwn hormones

    • high levels progesterone during pregnancy → prevent contractions

      • inhibit oxytocin while fetus develops

    • foetus grows larger + pushes against uterine wall → stress hormones released by baby + parent during last few weeks of gestation → oestradiol increase → inhibit progesterone release + increase density of oxytocin receptors in uterine wall (positive feedback effect)

    • uterine contractions + servical stretching stimulate posterior pituitary gland → oxytocin released → oxytocin binds to oxytocin receptors → stronger contractions → more contractions + cervix dilation

      • positive feedback loop

  • levels of oestradiol + progesteron decrease → menopause

    • reduction → increased risk of bone fractures + osteoporosis

  • Hormone replacement therapy (HRT) - treats w additional hormones to relieve symptoms of menopause

    • some ppl had reduced or increased incidence of coronary heart disease

  • flowers have both male (stamen) and female (carpels)

  • many plants produce sexually

    • sperm in pollen fertilizes egg in ovule

    • some hemaphrodites but still have sexual reproduction

  • pollination - transfer of pollen from male anther → female stigma

  • fertilization

    • occurs in ovary of the carpel (pistil)

  • seed dispersal - movement of seed away from parent plant

  • pollen lands on stigma of carpel → produces a pollen tube

    • tube grows down the style into the ovary → 2 sperm move down pollen tube → pollen tube enters ovule → fertilization

    • second sperm fuses w two polar nuclei → triploid endosperm

      • provides nutrients for actual embryo

  • Sepal

    • protects flower before blooming

  • petal

    • colorful/scented to attract insects

  • stamen

    • male part

    • filament + anther

  • filament

    • supports anther

  • anther

    • produces pollen w haploid sperm

  • carpel

    • female part

    • stigma, style, ovary

  • stigma

    • sticky tip

    • traps pollen

  • style

    • connects stigma + ovary

    • pollen tube grows down

  • ovary

    • contains ovules + haploid eggs

  • prevent self pollination

    • reduces genetic diversity → BAD

    • structural differences

      • different lengths of styles/stamen

    • temporal separation of male/female    

      • develop at different times

    • genetic incompatability systems

      • rejection by stigma based on self recognition of pollen genotype

  • mechanisms to promote cross fertilization !!

    • different maturation time for pollen + style

    • some plants have separate male + female flowers on same plant

    • some species have separate male + female plants

  • plants evolved to be pollinated by animals or wind

    • animal-pollinated (ANIMALS INCLUDES BUGS)

      • large, bright, scented petals

      • short stamens

      • low quantities of sticky pollen

        • attaches to bodies of animal pollinators

      • stigma inside flower

        • brushes against animals entering

    • wind pollinated

      • small reduced petals

      • stamens outside flower w long filaments

      • produce large quantities of light, feathery pollen

        • easily carried by wind

      • stigma outside flower

        • traps pollen as it blows past

  • germination - development/growth of plant embryo → seedling

    • Steps

      • water absorbed

      • gibberellins synthesized by embryo

      • gibberellin stimulates aleurone layer cells → synthesize amylase

      • amylase hydrolyses starch → maltose

      • maltose → glucose

      • glucose transported to embryo → energy for growth

    • use oxygen + glucose for aerobic respiration

    • respiring embryo uses nutrients in seed