Cell Differentiation: cells are genetically programmed to be specialized and will assume unique structural & functional attributes Fertilized Egg = totipotential stem cells vs. pleuripotential stem cells

Oocyte with sperm = fertilization Zygote=fertilized egg

Series of mitotic divisions = cleavage 2-cell stage (30 hours post fertilization)

Zygote 2-Cell Morula 16-32 Cells

8-Cell Stage…                                  

Morula= solid ball of cells (32 cells +)

Blastocyst=hollow ball of cells, implants in uterus 6-7 days after fertilization (500-2000 cells) Trophoblast= Chorion placenta Inner cell mass= embryo + amniotic sac

Embryonic disk develops from inner cell mass gastrulation= endoderm Somites mesoderm ectoderm (2nd week) = embryonic stage

Endoderm (inner layer)= -respiratory system -Pharnyx (throat) -Pancreas -Liver -GI tract Mesoderm (middle)= -gonads -kidneys -circulatory system -Somites = muscles, skeleton

Ectoderm (outer layer)= -skin -hair -inner ear -lens of eye -nervous system -connective tissues

Neurulation= nervous system forms (3rd week) (2mm long)

Spina Bifida

Anencephaly

Extraembryonic Membranes Trophoblast= placenta + chorion Inner cell mass= embryo + amniotic sac + allantois (bladder & umbilicus) + yolk sac (nutrients & germ cells)

4th week= Organogenesis -heart begins to beat (70 bpm) [2.5 billion beats per 70 years] -5 mm long -susceptible to teratogens [thalidomide]

2nd Month = Morphogenesis -arms, legs, tail bone form -25 mm long -major organs continue to form 6 week embryo

7th week= sexual differentiation occurs                                          

8th week embryo becomes a “fetus”

-most major organs are formed -placenta takes over pregnancy End of 1st trimester -most major organs are formed -placenta takes over pregnancy 2nd trimester (175 mm; 225 gm) -organs grow -nervous system continues development 3rd trimester -baby grows rapidly! -6th month=1.3 lbs; 1 ft long                             

What controls growth & development? GENES!                                         

Hutchinson-Gilford Syndrome (Progeria) 8 year old child with Hutchinson-Gilford Syndrome (Progeria)                                

Homeotic Genes (Hox)= act as switches and control pattern formation during development Dermatomes

Mutations: changes made in normal genetic sequence of DNA A. Cells have DNA repair mechanisms but… ~ 1 out of 1 billion mutations aren’t repaired B. If change affects last nucleotide of codon = okay if 1st codon affected = bad Why? [Overhead] C. Mutagens: agents which cause mutations (e.g., radiation… UV-B, X-rays, sodium nitrite, cigarettes

Mutations Point mutations: one nitrogen base gets substituted for another. Ex. DNA normally read as…. …GGTCTTCTC… UV radiation zaps and changes message to…. …GGTCATCTC The result is Valine gets substituted for Glutamine… causing the disease….

Sickle Cell Anemia

Sickle Cell Anemia:

e.g. Sickle Cell Anemia HbA HbS HbA/HbA HbA/HbS HbS/HbS ¼ normal; ½ sickle cell trait; ¼ sickle cell anemia

Sickle Cell Anemia and Malaria

Malaria & Sickle Cell Allele Distribution

Mutations b. Frame-shift: an extra nucleotide gets slipped into message… THE CAT RAN FAR….. THE QCA TRA NFA R c. Insertions: extra messages added THE FAT CAT RAN FAR d. Deletions: messages removed THE RAN FAR

A Deletion Mutation…

Mutations: e. Trisomy: extra chromosomes are added to our “Karyotype” = usually lethal

Trisomy 21 and Down’s Syndrome