Exam 3 Chapter 1 When Does Human Life Begin Fertilization and Pre Implantation Development o Zygote Cleavage Blastocyst Zygote single celled embryo Cleavage multiple cell divisions following fertilization early cell division Leads to formation of o Inner mass cells form the embryo o Trophoblast become the placenta extra embryonic o Blastocoel fluid filled space Blastocyst a 100 cell embryo The zona pellucida degrades after cleavage o Pre implantation can occur outside of the womb a k a in vitro or in a dish Post implantation CAN NOT o Fertilization human development begins by the fusion of female and male gametes egg and sperm Gametes have half the DNA of other cells They only have one of each chromosome instead of a pair meaning they are Haploid All other cells are Diploid meaning they have 2 chromosomes 2n Genome combination of all DNA in each cell of a person Genotype specific sequence of genes that helps determine phenotype Unique for each individual Creation of new genotype occurs when the pronucleus of the sperm and the pronucles of the egg fuse to create the nucleus of a zygote o DNA is contained in the nucleus Pronucleus the nucleus of a gamete which has only half the DNA Genes units of info in the DNA Gene expression use of the gene Gene repression not using the gene o Implantation Process where the blastocyst attaches to the mother s uterus and into the uterine lining Occurs 5 6 days after fertilization but usually not complete until end of Week 2 Chorion extra embryonic tissues of the child that develop from the trophoblast intermingle with the tissue of the uterine wall Forms the placenta Approx HALF of human embryos successfully implant other half are lost without awareness of pregnancy Premature hatching of the embryo from the zona pellucid the embryos shell must occur at right time premature hatching can lead to tubal pregnancy Tubal pregnancy embryo implants before it reaches the uterus Life threatening to mother Inability to hatch can lead to infertility o A woman is medically considered pregnant only after the embryo has been firmly implanted in the uterus o The First Trimester 60 days or 8 weeks Gestation period from implantation to birth Gastrulation and Germ Layer Formation days15 23 Knowledge of post implantation embryology is extremely primitive Gastrulation occurs around day16 where differentiation begins o Also when cells begin to move and communicate Differentiation ordered process where the single fertilized zygote produces all the different cell types Makes different cell types of the body somatic cells which are divided into three germ layers o Ectoderm skin and nervous o Mesoderm muscle blood blood vessels o Endoderm gut pancreas liver kidneys Makes the extra embryonic tissue which allows the exchange of wastes for nutrients with the mother Make the sex cells to reproduce Germ Cells the sperm and egg o Separated from the germ layers and kept in the Gonads testes and ovaries o Early separation prevents more divisions that could lead to mutation change in DNA sequence Fraternal twins result from fertilization of more than one egg in a single ovulation Identical twins genetically identical occurs from twinning Twinning two separate individuals come from one embryo occurring up to and during implantation Can no longer be formed after gastrulation begins Organogenesis Development after gastrulation Mark completion of 1st trimester about 1 3 embryos survive 1st Process of forming organs from basic plan laid down during gastrulation trimester Neuralation days21 25 beginning of Organogenesis formation of the neural tube becomes the brain and spinal cord Embryogenesis encompasses cleavage gastrulation and Organogenesis Describes developing offspring for the first 6 8 weeks after conception Fetus end of the 1st trimester day 56 or 8 weeks A fetus is neither male nor female sex is determined around week 11 Sex Determination o Meiosis cell division resulting in the formation of cells that have one of EACH chromosome Females and Males both give 23 chromosomes 22 are autosomal 1 is sex chromosome YY for females XY for males meaning males have the only X therefore the male chromosome dictates the gender of the offspring o Primary sex characteristics formation of gonads o Seconds characteristic physical traits and appearance o 2nd trimester o Consciousness o Birth 8 weeks Gonads form testes or ovaries 10 weeks Brain structure complete 12 20 weeks Mother first feels sensation of the baby called quickening 16 weeks first blood cells fingerprints and toeprints First sign that the brain is functioning first positive EEG at 25 weeks or 7 months Offspring s lungs mature mother s uterus is stimulated to contract Can NOT survive without medical assistance if born in 2nd trimester Chapter 2 Fertilization and Assisted Reproduction Gametogenesis formation of gametes o Spermatocyte developing sperm Oocytes developing egg Sperm consists of nothing but packaged DNA Acrosome explosive package to break through the egg shell Nucleus contains the DNA Mitochondria energy Centrole makes the Flagella the tail Fertilization process where Gametes fuse together o Localization penetration prevention of polysperm fusion of genetic material initiating development o Sperm activated binds to zona pellucid egg shell acrosomal reaction sperm makes hole in zona pellucid sperm and egg membranes fuse sperm enters egg o 92 of couples conceive within two years of trying o Fails when there is an inability to produce sufficient egg or sperm OR tubal blockage Can be genetic age smoking STDs body weight chemotherapy etc Males constantly replenish sperm throughout life Females produce all their Oocytes before they are born o IVF in vitro fertilization Artificial hormones given to woman to stimulate production of hormones Eggs collected Sperm collected and placed under thick solution to pick best swimmer 3 days after eggs retrieved and fertilized the best embryos are transferred to uterus Cell division occurs during certain time frame embryos developing too slow will not be picked PROBLEMS Women must take drugs larger chance of multiple births higher risk of tubal pregnancy collection process can lead to bleeding Can also lead to sperm mix ups clinics not properly cleaning sperm tube can end up in getting sperm from separate fathers Since IVF is fairly new there isn t much data on whether it produces healthy adults or not o Prenatal Diagnosis Sex Selection Determines genome of child Selection for certain
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