unit 13 development

the process whereby all diffrent cell types are produced through selective changes in the genetic activity

• fertilization: fusion of the male and female gametes
• embryological development: firdt 2 months after fertilization
• fetal development: from the begining of the 9th week until birth
• postnatal development: commences at birth

involves the fusion of 2 haploid gametes with 23 chromosomes each to produce a zygote that contains 46 chromosomes

occurs in the uterine tube within one day

the protective layer of cells

• 10,000 enter the tube
• less than 100 reach the egg

contains the hylurondase which breaks down the bonds between the cells of the corona radiata

• single sperm makes contact with the oocyte membrane
• it is activated and completes meiosis II which results in teh production of the second polar body. the oocyte has a single set of 23 chromosomes
• the sperm is absorbed into the oocyte cytoplasm

• a male pronucleus and female pronucleus form the fuse
• the result is the formation of a zygote with 2 pairs of 23 chromosomes (46 in all)

time spent in prenatal development

embryological development and early fetal development this trimester begins with fertilization the structure of all major organs systems appear

ddevelopment of the organs and organ systems. by the end of this trimester the fetus looks human

characterized by rapid fetal growth. early this trimester most of the organ systems become fully functional this trimester ends in birth