This document discusses several genetic and environmental factors that can influence human development. Genetic factors like pleiotropy and mosaicism can result in syndromes with multiple abnormalities. The same genetic mutation can also produce different phenotypes depending on gene interactions. Environmental teratogens during critical periods of embryonic development can irreversibly damage organ formation, with alcohol, retinoic acid, and endocrine disruptors like bisphenol A and atrazine posing particular risks like fetal alcohol syndrome, cleft palate, lower sperm counts, and cancer. Both genetic and environmental heterogeneity contribute to the complexity of human development.

1. Development in
Health and
Disease

2. Abnormal
Development

3. The Role of
Chance
In protein synthesis, there
are random fluctuations in
transcription and translation
Cell migration, cell
specification, and signaling
are all influenced by random
fluctuations

4. Genetic
Factors in
Human
Development
• A syndrome is when there are several abnormalities together.
They can be caused by:
• Pleiotropy-
• the production of several effects by a gene
• the addition of deletion of a gene in the chromosome
• There are different kinds of pleiotropy:
• Relational- a defective gene in one part of an embryo
• Mosaic- a gene is critical in different parts of the
body, so the effects are in multiple places
• Mosaic syndromes can result from aneuploids-
an error in the number of particular
chromosomes. Down Syndrome is an example.

5. Genetic and Phenotypic Heterogeneity
Genetic Heterogeneity is when
mutations in different genes can
cause the production of similar
phenotypes
• Alzheimer's disease is an
example. There are multiple
alleles responsible for the
symptoms
Phenotypic Heterogeneity is
when the same mutation
produces a different phenotype
in different individuals
• This is because genes often
interact with other genes

6. Environmental Effects on Animal Development
• Agents that cause birth defects are called teratogens.
• In embryonic development, there are critical periods when damage done is
irreversible
• This is found more in the embryonic period- when organ systems are
forming
• This happens through week eight
• The maximum damage can be done in weeks three through eight
• After this it is referred to as a fetal period
• In the fetal period there is mainly growth and remodeling.
• Examples of teratogens are drugs, chemicals, viruses and radiation

8. Alcohol
Alcohol is probably the worst
teratogen in terms of the
number of people it effects
Roughly 1 in 650 children are
born with fetal alcohol
syndrome (FAS).
• Those with FAS often have:
• Smaller brains
• Significantly Lower IQ
• Small head size
• Low nose bridge
Some studies suggest that
even two drinks in one sitting
can have a negative effect on
fetal brain cells

10. Retinoic Acid
• Retinoic Acid is important in many aspects of
the anterior-posterior axis specification.
• It is a derivative of vitamin A
• Accutane, used to treat acne, contains high
doses of retinoic acid
• This is often the same age group that might be
pregnant and not know for a while
• Neural crest cells might not migrate to the
pharyngeal arches
• This effects facial development like ears and
jaws. Another sign is a cleft palate

11. Endocrine Disruptors
These interfere with the endocrine
system during development. They can:
• Mimic the effect of a hormone
• Antagonize or inhibit a hormone
• Effect the synthesis, transportation,
or elimination of a hormone
• Make the organism artificially more
sensitive to a hormone later in life
Endocrine disruptors can be found
everywhere
• Plastic bottles
• Cans
• Pesticides and herbicides

12. Bisphenol A
(BPA)
Found in plastic bottles, cans, cash register
receipts among other places
Shown to affect the meiotic process in mice
Can cross the placenta
Causes higher miscarriage rates
May predispose women to breast cancer
later in life

13. Atrazine
Contains the enzyme aromatase which can
convert testosterone to estrogen
It is very common in weed killers
Studies have shown lower sperm counts and
decreased fertility in men