Gametogenesis Flashcards
What is the main goal of meiosis?
-reduce chromosome #s (diploid -> haploid in gametes)
-crossing over & exchange of genetic material between male-female chromatids
-produce 4 daughter cells (genetically distinct)
Describe gametogenesis.
-formation of male & female gametes
-sperm & ova from spermatogonia & oogonia
Describe mitosis.
-spermatogonia & oogonia (gonadal stem cells) multiply within gonad with a full set or diploid # of chromosomes (2N) specific to the species
Describe meiosis I & II.
-Spermatocytes & oocytes are produced & exchange genetic material between male & female chromatids
-divide to ensure haploid # of chromosomes (1N) in sperm & ova
Describe fertilization.
-sperm penetrates ovum to restore diploid # of chromosomes (2N) to make zygote
Describe the hypothalamic-pituitary-gonadal axis.
negative feedback
Gonads = endocrine & gametogenic functions
Describe primordial germ cells.
-primary undifferentiated stem cells that will differentiate into female & male germ cells = spermatogonia or oogonia = develop into mature male & female gametes = spermatozoa or ova through spermatogenesis or oogenesis
-PGCs appear during early embryo development
-PGCs proliferate & migrate toward genital ridge of developing gonad
Describe the male gonad (testis).
Key hormones:
-GnRH
-FSH
-LH
-testosterone
-inhibin
Key mechanism:
-LH -> leydig cells -> testosterone
-FSH -> Sertoli cells -> inhibin, ABP
Describe leydig cells.
-respond to LH to make testosterone or other androgens that help w sexual development & support to Sertoli cells
Describe Sertoli cells.
-respond to FSH to make inhibin & androgen binding proteins & nourish developing sperm cells
Picture of Sertoli & cells of leydig.
Describe spermatogenesis steps.
- spermatogenesis: begins at puberty when HPG axis matures & testosterone rises (continuous after puberty)
- mitosis: spermatogonia divide to make diploid primary spermatocytes
- Meiosis I: primary spermatocytes duplicate paternal & maternal chromosomes, homologous chromosomes crossover, exchange DNA, & divide to make haploid secondary spermatocytes
- Meiosis II: divide to make spermatids
- Maturation: transform spermatids to spermatozoa or sperm
Describe sperm characteristics.
-each sperm is genetically distinct
-X or Y chromosome
-acrosome of head = enzymes to penetrate ovum
-midpiece = mitochondria to make ATP (energy to propel sperm to site of fertilization)
Describe sperm morphology in species.
shape & size of sperm head + length is species specific
-disc = ruminants
-pear = man, stallion
-hook = rodents
-spoon = guinea pig
-filiform = bird
Describe the spermatogenic cycle & wave.
12 stages
-spermatogenic cycle = time of one cycle
-spermatic wave = distance between stages
Describe sperm storage & exit.
STORAGE:
lumen of seminiferous tubules -> rete testis -> efferent ducts -> head of epididymis -> body & tail (stored here)
EJACULATION:
Vas deferens -> urethra (mixes w seminal plasma) -> glans penis (exit)
desposition in female = vagina, cervix, uterus
Ovary of a bitch. (Picture)
Preovulatory follicle (picture).
Describe the female gonad (ovary) endocrine gland.
-follicle
-corpus luteum
Describe folliculogenesis.
-cohort of follicle growth
-follicle selection
Spermatogenesis VS oogenesis.
Folliculogenesis VS oogenesis.
Describe fertilization.
-union of 2 haploid gametes (spermatozoa & ovum) to restore the diploid state to form a zygote through process of ovum activation & start mitotic divisions = result in cell differentiation & embryo development
Describe the steps of fertilization.
- Sperm prep = capacitation & acrosome reaction
- Sperm-ovum fusion & penetration of sperm
- Sperm & ovum pronuclei fusion
- Activate zygote
Describe capacitation.
-maturation process in response to uterine & oviductal fluid secretion to prepare sperm for the acrosome reaction & fertilization
Describe acrosome reaction.
-acrosomal digestive enzymes released to start fusion with ovum & penetrate through zona pellucida & PM of ovum
Describe polyspermy.
-ovum is fertilization by more than one sperm
-too many centrosomes can be bad for survival of embryo
-block polyspermy: fast & slow
Describe fast block.
-change in electric potential of PM preventing fusion of sperm
-influx of Na
Describe slow block.
-cortical granules release enzymes = formation of a fertilization envelope around ovum
-release of Ca
Pro nuclear fusion. (Picture)
Pronuclei picture.
Gametogeneis VS embryology.
