objective 8 pt 2 Flashcards
consists of one stage
produces diploid cells
produces 2 idential daughter cells with the same number of chromosomes as parent cell
body cells
mitosis
consists of two stages
produces haploid cells
produces 4 genetically different daughter cells
gamete formation
involves two consecutive cell divisions but only one round of DNA replication
meiosis
what are the functions of meiosis?
- Number of chromosomes are cut in half (2n to n)
- Introduces genetic diversity, as all daughter cells are genetically different
from original cell
reduces chromosome number from 2n –> n
reduction division of meiosis
what are the stages of meiosis?
prophase, metaphase, anaphase, telophase
has events not seen in mitosis or meiosis 2
prophase 1
each chromosome is split in two and homologous chromosomes pair up forming tetrads consisting of 4 chromatids
synapsis
exchange of genetic material between chromatids
genetically called recombination
crossover (chiasmata)
the pairs of chromosomes become arranged in homologous pairs connected b y centromeres
metaphase I
the chromosomes are divided so that there are equal amounts on either side of the cell. as there are 46 chromosomes in a human cell, 23 end up on either side
anaphase I
the two daughter cells are completely divided, a nucleic envelope forms and the chromosomes become less visible. there are 23 chromosomes in each of these cells with chromosomal combination different from those originally present in the parent
telophase I
the two cells prepare to divide again
meiosis II
the chromosomes become visible, the nuclear envelope disappears and the centrioles form the spindle fibers
prophase II
the chromosomes line up along the middle
metaphase II
the chromosomes get split into its two stands of DNA
anaphase II
the cells are compleatly divided. the nucleic envelope reforms and four new cells with different DNA are created
telophase II
production of sperm in seminiferous tubules; begins at puberty
spermatogenesis
the diploid (2n) immature sperm cells
dividing by mitosis
spermatogonia
give rise to sperm
spermatogenic cells
what are the 3 steps of spermatogenesis
mitosis
meiosis
spermiogenesis
spermatogonia (stem cell) forms spermatocytes
each mitotic division yields 2 daughter cells
mitosis (spermatogenesis)
spermatocytes form spermatids (haploid male gamete)
meiosis (spermatogenesis)
primary spermatocyte (2n) undergoes ___, forming 2 secondary spermatocytes
meiosis 1 (spermatogenesis)
each secondary spermatocyte (n) rapidly undergoes _____ to become two spermatids (n)
meiosis II (spermatogenesis)
spermatids become functional sperm
spermiogenesis
spermatid elongates and forms a tail to become…
spermatozoon
what are the major regions of sperm?
head
midpiece
tail
genetic region that includes nucleus and helmetlike acrosome containing hydrolytic enzymes that enable sperm to penetrate egg
head
metabolic region containing mitochondria that produce ATP to move tail
midpiece
locomotor region that includes flagellum
tail
- Extend through wall of tubule and surround
developing cells - Provide nutrients and signals to dividing cells
- Move spermatocytes and spermatids along to the
lumen - Secrete testicular fluid into lumen for sperm
transport - Phagocytize faulty germ cells and excess
cytoplasm - Produce chemical mediators to regulate
spermatogenesis
sertoli cells (large supporting cells)
tight junctions in sustenocytes form ____
* Prevents sperm antigens from escaping into
blood and causing activation of immune system
* Sperm is not formed until puberty, so it is
absent during immune system development
* Results in sperm not being recognized as
“self”
* Therefore, sperm needs to be kept separated
from rest of body to avoid being attacked by
immune system
blood testis barrier
how long does spermatogenesis take?
64-72 days if conditions are hospitable
- Production of gametes and sex
hormones is regulated by
sequence of hormonal events
involving hypothalamus,
anterior pituitary gland, and
testes
hypothalamic-pituitary-gonadal axis (HPG)
what hormones does HPG involve?
GnRH, FSH, LH, testosterone, and inhibin
what are the sequence of events of hypothalamic-pituitary-gonadal axis?
- Hypothalamus releases gonadotropin-releasing
hormone (GnRH) - GnRH binds to receptors on anterior pituitary,
causing them to secrete:
* Follicle-stimulating hormone (FSH)
* Lutenizing hormone (LH) - FSH stimulates spermatogenesis indirectly by
stimulating sustentocytes to release androgen-
binding protein (ABP)
* ABP keeps concentration of testosterone high
promoting spermatogenesis - LH binds to receptors prodding them to secrete
testosterone
* Rising testosterone levels trigger
spermatogenesis - Testosterone entering blood stimulates sex
organ maturation, development/maintenance
of secondary sex characteristics, and libido - Rising testosterone levels inhibit GnRH release and
gonadal hormone release - Inhibin: released by sustenocytes when sperm count
high; inhibits GnRH and FSH release
