Prenatal development

somatic cells

all cells in body that aren’t gametes

• diploids (2n) = 2 sets of chromosomes

• divide by mitosis

gametes

sex cells - haploid (n) = 1 set of chromosomes

• divide by meiosis

meiosis 1

1. prophase 1 - homologous chromosomes condense, pair up and crossing over

2. metaphase 1 - line up along metaphase plate

3. anaphase 1 - homologous chromosomes separate to opposite poles

4. telophase 1 - cell divides into two haploid cells (each cell has 2 non-identical chromatids)

meiosis 2

1. prophase 2 starting cells are haploid and condense

2. metaphase 2 - line up along plate

3. anaphase 2 - sister chromatides separate to opposite ends

4. telophase 2 - cell divides into four non-identical haploid gametes.

3 phases of prenatal development

1. zygote period - 0-14 days conception to implantation tino wall of uterus

2. embryo period -3-8 weeks - major organs are formed

3. fetus period - 9th week until birth - major organs begin to function and developing organism grows

zygote period

zygote dives and redivides via mitosis to form blastocyst

what does blastocyst form

differentiates into 3 layers

1. ectoderm (upper) - forms epidermis, nails, teeth and sensory organs and nervous system

2. mesoderm (middle) - forms dermis, muscles, skeleton and circulatory and excretory system

3. endoderm (lower) forms digestive system, liver, salivary galnds and respiratory system

placenta, umbilical cord and amniotic sac also forms from blastocyst cells

mitosis

1. interphase - DNA has been copied but uncondensed

2. prophase - chromosomes condense and spindle forms

3. metaphase - lines along plate

4. anaphase - sister chromatids separated to different poles

5. telophase and cytokinesis - 2 identical diploid cells

mono vs dizygotic twins

• mono - 1 zygote splits into 2 embryos

• di - 2 eggs fertilised

cephalocaudal growth

head-to-toe direction - head and upper body developing before the lower body.

proximodistal

development occurs from the center of the body outward towards the extremities.

support structures

• amnion - watertight sace filled with fluid = cushion, regulates temp and weightless environment

• chorion - membrane surrounding amnion that becomes lining of placenta

• allantois forms umbilical cord

neural tube

u-shaped groove formed down centre of ectoderm - tops of groove move together and fuse creating neural tube

• 1 end swells and develops into brain rest becomes spinal cord

fetal learning

in last 3 months, CNS developed enough for learning

• habituation - decreased response to repeated stiumuli response returns with a new stimulus (dishabituation) - visual and auditory stimuli

• neonate association learning - parent’s voice and conditioning to taste stimuli

teratogens

external environmental agents that can cause damage or death during prenatal period

fetal alcohol syndrome disorder (FASD)

set of symptoms including lower birth weight, lack of responsiveness and arousability, increased occurrences of heart and respiratory abnormalities in infants, and impacts cognitive and behavioural functioning

thalidomide

drug used in late 1950s-60s to treat morning sickness or as sedative = babies born with defects

• sensitive period - major limb deformities if taken 4-6 weeks after conception

• 21 days - born without ears

• 25-27 - no arms or deformed arms

• 28-36 - derformed/no legs

• 40+ days - usually no effect