Chapter 21 : Development and aging
Fertilization begins when sperm & egg unite
One sperm fertilizes the egg
Only one sperm can succeed : 2nd stage of meiosis is only completed when a sperm makes contact => Then,
secondary oocyte is surrounded by a protective covering ‘ZONA PELLUCIDA’ and a layer of granulosa cells from
the follice ‘CORONA RADIATA’.
When sperm encounters egg, tip of its head ‘ACROSOME’ releases enzymes=> digest path between granulosa cells
of corona radiata, thru zona pellicuda to the oocyte plasma membrane => When first one makes contact, special
protein “keys” of sperm recognize receptor protein “locks” in oocyte plasma membrane => plasma membranes of
egg & sperm fuse => sperm nucleus can enter the egg = begin of FERTILIZATION => triggers 2nd meiosis & formation
of haploid OVUM (= mature egg).
Fertilization is complete when both haploid nuclei form a SINGLE diploid cell or zygote with 46 chroms.
The cytoplasm of the egg must support 2-weeks of cell division until the ‘pre-embryo’ makes contact with the
uterine lining and begins to receive nutrients from the mother.
PAGINA 559 GROTE FIGUUR en FIGIIR 56O en 567
Twins may be fraternal or identical (changes 1/90)
Fraternal: ovulation of more than one oocyte
Identical : from one zyogte => up to 8-cell stage, all cells of pre-embryo are identical. Ball of cells breaks before
differentation has begun.
Development : Cleavage, morphogenesis, differentiation & growth
Cleavage : cell divisions (no growth or differentiation). First 4 days => Ball of identical cells with same size as original
zyogte. Only energy is stored in cytoplasm + little glycogen in oviduct.
Morphogenesis : changes in form & shape
Differentiation : cells take specialized form & functions (= primary cause of morphogenesis)
Growth : starts when embedded in endometrial lining of uterus (nutrients from mother)
Pre-embryonic development : The first 2 weeks
Fertilization begins when sperm & egg unite
One sperm fertilizes the egg
Only one sperm can succeed : 2nd stage of meiosis is only completed when a sperm makes contact => Then,
secondary oocyte is surrounded by a protective covering ‘ZONA PELLUCIDA’ and a layer of granulosa cells from
the follice ‘CORONA RADIATA’.
When sperm encounters egg, tip of its head ‘ACROSOME’ releases enzymes=> digest path between granulosa cells
of corona radiata, thru zona pellicuda to the oocyte plasma membrane => When first one makes contact, special
protein “keys” of sperm recognize receptor protein “locks” in oocyte plasma membrane => plasma membranes of
egg & sperm fuse => sperm nucleus can enter the egg = begin of FERTILIZATION => triggers 2nd meiosis & formation
of haploid OVUM (= mature egg).
Fertilization is complete when both haploid nuclei form a SINGLE diploid cell or zygote with 46 chroms.
The cytoplasm of the egg must support 2-weeks of cell division until the ‘pre-embryo’ makes contact with the
uterine lining and begins to receive nutrients from the mother.
PAGINA 559 GROTE FIGUUR en FIGIIR 56O en 567
Twins may be fraternal or identical (changes 1/90)
Fraternal: ovulation of more than one oocyte
Identical : from one zyogte => up to 8-cell stage, all cells of pre-embryo are identical. Ball of cells breaks before
differentation has begun.
Development : Cleavage, morphogenesis, differentiation & growth
Cleavage : cell divisions (no growth or differentiation). First 4 days => Ball of identical cells with same size as original
zyogte. Only energy is stored in cytoplasm + little glycogen in oviduct.
Morphogenesis : changes in form & shape
Differentiation : cells take specialized form & functions (= primary cause of morphogenesis)
Growth : starts when embedded in endometrial lining of uterus (nutrients from mother)
Pre-embryonic development : The first 2 weeks
