Understanding Fertilization: Meiosis, Mitosis, and the Formation of Gametes, Slides of Family and Consumer Science

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Fertilization

Concept 2

Overview

• Babies can’t happen

without pregnancy.

• Pregnancy can’t happen

without fertilization.

• Fertilization can’t

(naturally) happen without

copulation.

• Copulation can’t result in

offspring without an egg

and a sperm.

• So where do these cells come

from??

Review

Starts with: Meiosis

Ends with:

But then how does this

happen??

But then how does this

happen??

Review

• Mitosis : the process of cell division that makes

identical copies of somatic cells

• Produces identical diploid body cells
  • Diploid = 2 full sets of chromosomes (so all 46 in humans!)
• After fertilization the zygote does mitosis repeatedly, and these identical cells will later differentiate and organize into specific tissues à organs à organ systems to make up the organism

Creation of diploid somatic cells Throughout your life Throughout body For growth and repair PMAT once 2 identical diploid somatic cells Creation of haploid sex cells Females: before you are born; Males: throughout life In the gonads (ovaries and testes) To make babies PMAT twice 4 unique haploid gametes Sexual

Review

Asexual

Spermatogenesis

• The process of forming male gametes
  • Occurs in the seminiferous tubules of the testes
  • At puberty (around 14 years in males) , the release of

testosterone causes this process to start and continue

throughout life

• Takes 1 spermatogonium cell and makes 4 spermatids
  • Must go through spermiogenesis to become motile

Sperm

3 parts:

• Head : genetic region; contains flattened nucleus and compacted DNA - Acrosome = surrounds the nucleus and secretes hydrolytic

enzymes that will help the sperm penetrate the egg

• Midpiece : metabolic region; packed with mitochondria
• Tail : locomotor region; flagellum that propels the sperm

Oogenesis

• The process of forming female gametes
  • Occurs in the ovaries
  • Females are born with all of the primary oocytes (early eggs) they will ever have - Meiosis in these cells has ”paused” in late prophase I and will resume after puberty begins à Secondary oocytes
  • Secondary oocytes do not finish meiosis until fertilization occurs
  • Takes 1 oogonium cell and makes 1 functional gamete = ovum (egg) - The other 3 are “polar bodies” that degenerate

Follicles

• Each primary oocyte is contained in an ovarian follicle = a cluster of cells that all nourish 1 oocyte - Primordial follicles : the follicles in the fetus - The majority of these remain dormant, stuck in prophase 1 - 99.9% go through atresia = apoptosis of the follicle and its surrounding cells #1 = primordial follicles

Follicles

• After puberty begins, FSH causes 20 or less follicles to be “recruited” a month, developing into primary follicles à secondary follicles à vesicular follicles #2 = primary follicle
• Only one will develop into the dominant follicle that escapes atresia and is ovulated - The secondary oocyte in the dominant follicle is the only one that actually resumes meiosis I #3 = developing follicle #4 = dominant follicle #5 = ovulation #6-8 = formation and degradation of corpus luteum

Fertilization

• When a sperm’s chromosomes combine with

those of an oocyte to form a fertilized egg

( zygote )

• Sperm first has to reach the ovulated secondary oocyte in the Fallopian tube - Must make it into vagina à cervix à uterus à Fallopian tube
• Must also go through capacitation = the biochemical process that changes the sperm so that it will be able to penetrate the oocyte and thus fertilize the egg