proceeds from simple undifferentiated state to more complex, differntiated condition 

occurs b/c of regulation of gene activity

breakdown of the body in old age

• senescence due to accumulation of free radicals from metabolism
• antioxidants-eliminate free radicals 

• 1st-all major organs appear
• 2nd-completes organ develp.
• 3rd-rapid fetal growth

fertilization-8 weeks

fertilization

cleavage

blastcyst formation

implatation

fertilization

• usually occurs w/i 24 hrs of ovulation
• usually in fallopian tubes
• sperm-200 mill in vagina
• 2 mill in cervix
• 200 at 2^o oocyte
• sperm-acrosome's enzymes allow penetrartion of 2 layers around oocyte
• oocyte finishes meiosis II
• usually in fallopian tubes

contractions in female 

move sperm

cell divisions w/ no increase in size

• occurs w/i fallopian tubes
• monozygotic (identical) twinning may occur (1st 8 days)
• dizygotic twins (non-identical twins)- from fertilization of > 1 egg
• results in morula (solid center) comprised of blastomeres ( cells)

• occurs in fallopian tubes
• morula enlarges and becomes a hallow ball of cells
• trophoblast-outer layer of cells (eventually becomes placenta)
• blastocoel-hallow inner cavity
• embryoblast-embryonic tissue
• also called inner cell mass

• blastocyst attaches to endo metrium-uterus
• embryoblast toward wall
• endometrium-more vascularized

• 2 parts
• secretes enzymes-able to get into urine lining 
• secretes human chorionic gonadotropin 

Human choronic gonaotropin

hCG

maintains corpus luteum- p & e, prevents menstruantion

• formation of germ layers
• occurs during embryonic pd
• embryonblast folds in on itself (=blastopore), creating 3 layers:
• endoderm: inner (forms the gut)
• eventually all structures of digestive, urinary, & respiratory systems
• mesoderm-middle
• eventually muscular, skeletal, & cardiovascular systems
• ectoderm-outer
• nervous system, skin, &hair

coelom

also forms

membrane-lined inner body cavity (peritoneum and pleura)

1. yolk sac
2. amnion
3. chorion
4. allantois

surrounds embryo, keeps amniotic fluid in place

fluid shock absorber

formerly trophblast, becomes placenta

• secretes human chorionicgonadotropin (hCG)-stimulates the corpus luteum to continue prod. of progesterone and estrogen
• human chorionic somatomammotropin (hCS) aka human placental lactogen-inceases in proportion to placental mass, reaching maximum levels after 32 weeks and remaining relatively constant after that 

• pregesterone secretion by corpus luteum maintains endometrium
• primary source of nourishment
• until placenta built

(3rd-9th month)

• functional placenta (embryo now a fetus)
• increase in size of structures created durig gastrulation
• increase in height-hair vs. smooth -1/2 weight after
• decrease in proportion of head size- 1/2-1/4 length of body 
• limbs -1/8-1/2 length of body  

birth (9th month)

• dialation
• expulsion
• placenta

uterine contraction to expel fetus

controlled of oxytocin (+ feedback loop)

after birth expelled

produces corticotropin-releasing hormone (CRH)-part of the clock tht establishes timing  of birth

outward expression of the genotype

-physical appearance 

heterozygote is intermediate-1-2 alleles

~red allele, white allele produce pink phenotype

~~human example: sickle cell anaemia

heterozygous expresses bothe alleles

~e.g. red & whitet allele prod. fur composed of some red and white hairs 

~human example=bl types

1 gene that influences prod. of more than 1 aspect of the phenotype 

~sickle cell allele

1. males=xy; female=xx
2. non-disjunction
3. 4 chromosomes necessary
4. specific gene-SR4 (sex determining region of 4)

failure of homologs to seperate during meiosis I

• in sex chrom. can result i
• turner's syndrome=x (phenotype female)
• Klinefelter's syndrome= xxy (phenotype male)
• shows that presence of 4 (& not # of x) determines sex in humans 

carried on x chrom.

1. more often expressed in males
2. often expressed in alternating generations
3. ex. color blindness
• x⁺=normal; x^c=color blindness

sex determining region of Y

• needs to be present & functional
• if genotype is XY but SRY defective-phenotype will be female
• cells do not recognie Ts, XY ind. phenotype will be female 

• genes on 22 pairs of regular chrmosomes
• may skip generations if recessive
• occur in males & female 
• albinism
• recessive trait-defect in prod. of melanin
• results in absence of pigment in skin, hair,eyes

• off spring - 50% chance of inheriting
• ex. huntington's disease
• degenerative disorder-affects basal ganglia region-muscle coordination
• chromosome 4

• proportion of individuals w/ gene who develop disease
• due to environment, gene interactions
• ex. BRCA I & II
• not all inds. who have gene develop breast or ovarian cancer
• if 100% then complete penetrance
• ex. huntington's disease

• trait expressed
• even though ind. may have trait severity differs betw inds. 
• i.e. phenotypes differs betw inds. w/ same genotype
• environment, gene interaction
• ex. emphysema (loss of elasticity in lungs)
• gene-a/AT
• smoking-increase severity
• both imcomp. pent. & var. express. diff. phen., same genotype

PKU-newborns

BRCA I & II- 1990s

TCFTLR- susceptible to type 2 diabetes