A. Internal Fertilization 1. Penis deposits sperm into the vagina 2. Fertilization of the egg usually occurs in the fallopian tubes (oviducts)

In humans: Sperm (n) Egg (n)Zygote (2n) 3. Sperm and egg combine chromosomes to form a zygote += 23 46

Brief Review

1.Sex cells that unite during fertilization, forming a single cell known as a ______________. zygote 2. The normal diploid chromosome number of a fruit fly is 8. How many chromosomes would a normal zygote of a fruit fly contain? 3. Compared to animals that carry on external fertilization, animals that carry on internal fertilization A. reproduce in water C. produce fewer eggs B. reproduce by sporesD. produce more eggs 8

B. Internal Embryonic Development 1. Cleavage: Repeated mitotic division of the embryo Cell number increases but individual cell size decreases

2. Embryonic Stages: a) Zygote:Single-celled embryo b) Morula:Solid ball of cells c) Blastula (blastocyst):Hollow ball of cells; filled with fluid d) Gastrula:Embryo consisting of 3 cell layers (germ layers)

3. Gastrulation Endoderm: inner layer Mesoderm: middle layer Ectoderm: outer layer a) One side of blastula indents to form the gastrula b) Consists of 3 germ layers:

Endoderm  digestive and respiratory systems, parts of the liver and pancreas Ectoderm  nervous system, skin, hair, nails Mesoderm  muscles, circulatory system, skeleton, excretory system, reproductive system 4. Differentiation: Embryonic stem cells become specialized * Occurs during gastrulation

C. Internal Development in Placental Mammals 1. Embryo develops in uterus 2. Placenta: temporary organ that exchanges gases, nutrients, and wastes between mother and child 3. Umbilical Cord: 4. Amniotic Fluid: protects attaches embryo to placenta embryo from shock

Human Development at 6 weeks Human Development at 4 months

D. Prenatal Development (Pregnancy) 1. Mother should: a. Eat nutritious foods c. Receive proper medical attention b. Avoid alcohol, tobacco, and drugs regularly

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Drug-Induced Birth Defects *Although the blood of the mother and baby never mix, certain chemicals are able to pass through the placenta to the baby’s blood. A. Fetal Alcohol Syndrome: Heart defects Facial abnormalities Low birth weight Slow development Mental retardation B. Cigarette Smoke: Placental problems Low birth weight Heart defects Asthma Correlated with SIDS

Some additional info…

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