Download Zygote (2n)

A. Internal Fertilization
1. Penis deposits sperm into the vagina
2. Fertilization of the egg usually occurs in the
fallopian tubes (oviducts)
3. Sperm and egg combine chromosomes to form a zygote
In humans:
23
+
Sperm (n)
23
Egg (n)
=
46
Zygote (2n)
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?
8
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 spores D. produce more eggs
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
a) One side of blastula indents to
form the gastrula
b) Consists of 3 germ layers:
Endoderm: inner layer
Mesoderm: middle layer
Ectoderm: outer layer
4. Differentiation: Embryonic stem cells become
specialized
* Occurs during gastrulation
• Ectoderm  nervous system, skin, hair, nails
• Mesoderm  muscles, circulatory system,
skeleton, excretory system, reproductive system
• Endoderm  digestive and respiratory
systems, parts of the liver and pancreas
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:
attaches embryo to
placenta
4. Amniotic Fluid: protects
embryo from shock
Human Development at
6 weeks
Human Development at
4 months
D. Prenatal Development (Pregnancy)
1. Mother should:
a. Eat nutritious foods
b. Avoid alcohol, tobacco, and drugs
c. Receive proper medical attention
regularly
Where
are my arms???
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:
•Slow development
•Heart defects
•Facial abnormalities •Mental retardation
•Low birth weight
B. Cigarette Smoke:
•Placental problems
•Low birth weight
•Heart defects
•Asthma
•Correlated with SIDS
Some additional info…
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