BSC1005 Exam 3 Chapter 1 DNA is packaged and contained in nucleus Pronucleus the nucleus of a gamete which has only half the DNA of other cells when the sperms pronucleus first enters the egg both the pronucli migrate toward each other creation of a new genotype occurs when the pronucleus of the sperm and the pronucleus of the egg fuse to from the nucleus of the zygote this leads to the formation of Inner mass cells form what is known as the embryo Trophoblast become the placenta not the embryo itself extra embryonic Blastococl fluid filled space Pre implantation but not the post implantation can occur outside of the mothers s womb in a dish After cleavage the zona pellucida degrades During the first week following ovulation the egg is fertilized while traveling down the oviduct divides through a process called cleavage to form a morula and later a blastocyst until it reaches the uterus where it undergoes implantation in the uterine wall cited from Human Reproduction in the 21 st century Implantation second week is over The process blastocyst attaches to the mothers uterus and buries itself into the uterine lining This occurs between days 5 and 6 after fertilization but usually not fully completed until the Chorion an extra embryonic tissue of the child that develops from the trophoblast intermingle with the tissue of the uterine wall deciduas this froms the placenta approx only one half of the human embryos successfully implant the other half become lost without the awareness of pregnancy the embryo must hatch from the shell zona pellucid in order to implant hatching from the zona pellucid must occur at the right time and right place if not premature hatching occurs which can lead to a tubal pregnancy in turn tubal pregnancy is the embryo implanting before it reaches the uterus note that this is life threatening for a mother an inability to hatch can lead to infertility When is a woman considered pregnant in the medical community she is not considering pregnant until the embryo has been firmly implanted into the uterus After the blastocyst attaches to the uterine lining the ICM cells proliferate increase in number according to cell division ICM cells also expand to create amniotic cavity where the embryo itself will develop amniotic cavity contains fetal cells that can be drawn for diagnostic tests in the process known as amniocentesis The first trimester 60 days or 8 weeks gestation the period from implantation to birth our knowledge of post implantation human embryology is extremely primitive Cell lineages the family tree of what kind of cells are made at each cell division gastrulation and germ layer formation days 15 through 23 differentiation many cells in the human body the ordered process by which the single fertilized zygote produces all these different cell types 3 major purposes to differentiation in mammals 1 make different cell types of the body somatic cells 2 make the cell types and structures that allow the exchange of wastes for nutrients with the mother extra embryonic tissue 3 make the cell types that ensure the next generation germ cells Somatic cells are divided into 3 germ layers nothing to do with germ cells though 1 ecoderm skin and nerves 2 mesoderm muscle blood blood vessels 3 endoderm gut pancreas liver kidneys all cells have the same genetic info but each cell only listens to some and ignore other genes present unit of info within DNA genes gene expression use of genes gene repression not using the genes extra embryonic tissue largely derived from trophoblast which goes to placenta amnion amniotic cavity protective sac in which the embryo develops allantois embryos first toilet gastrulation occurs roughly at day 16 after fertilization the stage in which differentiation of the embryo begins also marks the stage where cells begin to move and communicate with each other which means tell each other what kind of cells to communicate with cell communication identical twins can no longer be formed after gastrulation begins fraternal twins result from fertilization of more than 1 egg in a single ovulation related genetically like two siblings but born at same time identical twins genetically identical twinning which can occur in many stages early in embryogenesis splitting of the embryo before implantation twinning produces 2 separate individuals from a single embryo and can occur up to and during implantation during gastrulation organogenesis marks the completion of the first trimester 1 3 embryos survive this first trimester development after gastrulation process of forming organs from the basic plan laid down days 21 through 25 neuralation which is the beginning of organogenesis or the formation of the neural tube later this becomes the brain spinal cord Second Trimester 8 weeks week 8 gonads testes or ovaries form Actual genitalia surfaces about 11weeks week 10 brain structure not the function complete 61 68 days weeks 12 through 20 quickening mother first feels sensation of the baby week 16 first blood cells finger prints and toe prints embryogenesis encompasses cleavage gastrulation and organogenesis and describes the developing offspring for the first 6 to 8 weeks following conception Sex determination Meiosis cell division that results in the formation of cells that have 1 of each chromosome Females have 23 pairs of chromosomes including their 22 autosomal chromosomes non sex chromosomes Males have 22 pairs of autosomes and 1 x and 1 y Males determine sex of children either by donating the x for a girl or a y for a boy primary sex characteristics formation of gonads secondary sex characteristics everything else ie body fat hair muscle mass voice tone bone structure etc Ex testosterone is secreted by testes These in time bind to testosterone receptors Someone with AIS androgen insensitivity have normal testes but lack testosterone receptors thus these males often resemble a female both socially and physically but genetically are still a male Consciousness Birth first positive EEG sign that brain is functioning was at 25 weeks 7 months offsprings lungs mature mothers uterus is stimulated to contract the fetus can t be born and survive in the second trimester without medical assistance Chapter 2 Fertalization and Assisted Reproduction Vocabulary Gametogenesis Formation of Gametes Spermatocyte is the developing sperm Sperm a mean clean DNA machine consisting of nothing but packaged DNA Acrosome Explosive package to break through the egg shell Oocytes is
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