Meiosis & the Gametes

What is meiosis?

cell division, where gametes (sperm cells or oocytes) are formed

What are replicated chromosomes (double-stranded chromosome)?

chromosome with 2 identical sister chromatids

What is a pair of chromosomes?

1 maternal and 1 paternal chromosome - humans have 23 pairs

What is a diploid?

a cell with 2 copies of each chromosome

What is a haploid?

a cell with a single copy of each chromosome

What happens during interphase?

DNA is replicated - cell has 23 pairs of replicated chromosomes - diploid

What happens in prophase 1?

homologous double-stranded chromosomes pair up - crossing over occurs - diploid

What happens in metaphase 1?

pairs of homologous chromosomes line up in the middle of the cell and spindle fibers attach to replicated chromosomes - diploid

What happens during anaphase 1?

pairs of homologous chromosomes separate and pulled to opposite ends of the cell - diploid -> haploid

What happens during telophase 1?

cell finished 1st mitotic division, producing 2 daughter cells - daughter cells have 23 replicated chromosomes (parent cell had 23 pairs, but daughter cells only have 23 chromosomes) - haploid

What happens during prophase 2?

replicated chromosomes gather - crossing over does not occur - haploid

What happens during metaphase 2?

replicated chromosomes align at the center of the cell - spindle fibers attach - haploid

What happens during anaphase 2?

sister chromatids pulled apart to opposite ends of the cell - become single stranded chromosomes - haploid

What happens during telophase 2?

4 cells (gametes) produced, each with 23 single stranded chromosomes - cytokinesis begins - haploid

What is nondisjunction?

a process by which the chromatids fail to properly separate during meiosis

What is trisomy?

an extra copy pf chromosome (24 chromosomes)

What is monosomy?

a single/missing copy of a chromosome (22 chromosomes)

What are spermatogonia?

"stem cells" that help produce sperm - contain 23 PAIRS of chromosomes (total 46 - diploid) - divide by mitosis

What are sustentacular cells?

cells that support, protect, and nourish the developing sperm

After spermatogonia divide my mitosis, what do they produce?

primary spermatocytes

What are primary spermatocytes?

cells that have 23 PAIRS of chromosomes (46 total - diploid) - divide by meiosis

After primary spermatocytes divide by meiosis, what do they produce?

secondary spermatocytes

What are secondary spermatocytes?

cells that contain 23 chromosomes only (haploid)

After secondary spermatocytes finish the second meiotic division, what do they produce?

spermatids

What are spermatids?

immature sperm - contains 23 chromosomes only (haploid)

What do spermatids develop into?

sperm (spermatozoa)

What do sperm shed to develop their head, midpiece, and tail?

the cytoplasm from the spermatid

Sperm head components

nucleus/DNA and acrosome cap (enzymes)

Sperm midpiece components

mitochondria

Sperm tail components

flagellum

Where is sperm released from and then eventually enter into?

the sustentacular cell cytoplasm, and enter the lumen of the seminiferous tubule

What is a primordial follicle?

a primary oocyte + single layer of flattened (squamous) follicle cells

What is a primary follicle?

primary oocyte + layer of cuboidal cells

What are follicle cells called?

granulosa cells

What is a secondary follicle?

primary oocyte + multiple layers of granulosa ells

What is an antral follicle?

primary oocyte + granulosa cells + antrum

What does a mature follicle cell contain?

secondary oocyte

What is the corpus luteum?

the ruptured follicle what underwent ovulation - yellowish

What is the function of the corpus luteum?

secrete estrogen and progesterone

What is the curpus albicans?

degenerated corpus luteum - white connective tissue scar

During oogenesis, what occurs before birth (during the fetal period)?

oogonia (oocyte "stem/parent cells") - contain 23 pairs of chromosomes (46 total) - primary oocytes start process of meiosis but stop at prophase 1 - ovary will contain primordial follicles (which have primary oocytes in them)

During oogenesis, what occurs during childhood?

ovary is inactive - primordial follicles contain primary oocytes stuck in prophase 1

During oogenesis, what occurs at puberty?

anterior pituitary secrets FSH and LH which stimulate follicle development - about 20 primordial follicles develop into primary follicles - some primary follicles degenerate while other become secondary and antral follicles - usually one antral follicle develops into a mature follicle

In the mature follicle at puberty what happens?

the primary oocyte in the mature follicle completes meiosis 1 but gets (re-)stopped in metaphase 2

What type of oocyte do you end with at puberty?

secondary oocyte

What hormone causes ovulation?

LH

What day does ovulation usually occur at?

day 14

During oogensis, what occurs during ovulation?

a peak in LH induces ovulation - a secondary oocyte is ecpelled - oocyte is still suspended win metaphase 2 and will not complete meiosis until it is fertilized by a a sperm

During oogensis, what occurs after ovulation?

FSH and LH levels decline - ruptured ovarian follicle becomes the corpus luteum - corpus luteum eventually becomes a corpus albicans