Chapter 4, the biological and environmental causes of disease

2. discussed by:
LESTER, NORIEL,
GIAN, MANAMAY
Subject : FTC
THE BIOLOGICAL AND
ENVIRONMENTAL CAUSES
OF DEVELOPMENTAL
DISABILITIES

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Basic concepts of human reproduction
Heredity- the mechanism for the transmission of human
characteristics from one generation to the next.
Genome- genetic code; complete set of coded instructions for
making and maintaining an organism. Inherited from both parents.
• Chromosomes- are thread-like structures located inside the
nucleus of animal and plant cells. Each chromosome is made of
protein and a single molecule of deoxyribonucleic acid (DNA).
Passed from parents to offspring, DNA contains the specific
instructions that make each type of living creature unique.

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Deoxyribonucleic acid (DNA) -long threadlike molecule
and genetic substance. Is a complex molecule that contains
the genome.
Double helix- two strands of twisted ladder-shaped
structure that wrap around each other.
Gene - specific sequence of the four nucleotide bases
whose sequences carry the information for constructing
proteins.

5. Dominant-Recessive Genes Principle • The principle that if one
gene of a pair is dominant and the other is recessive, the dominant
gene exerts its effect, overriding the potential influence of the
recessive gene. A recessive gene exerts its influence only if both
genes in the pair are recessive.
Sex-linked Genes Principle A particularly important category of
genetic linkage has to do with the X and Y sex chromosomes. These
not only carry the genes that determine male and female traits but
also those for some other characteristics as well. Genes that are
carried by either sex chromosome are said to be sex linked.
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Some Principles of Genetic Determination

6. Men normally have an X and a Y
combination of sex chromosomes,
while women have two X's. Since only
men inherit Y chromosomes, they are
the only ones to inherit Y-linked traits.
Men and women can get the X-linked
ones since both inherit X
chromosomes.
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Some Principles of Genetic Determination

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Polygenic Inheritance Principle
Poly (many) genic (genes)
inheritance describes the
interaction of many genes to produce
a particular characteristic.
Considering that there are as many as
140,000 genes, the huge number of
combinations possible is hard to
imagine. Traits that are produced by
the mixing of genes are sais to be
polygenically determined.

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Genotype
The Genotype is that part (DNA sequence) of the genetic makeup of a cell, and therefore of an organism or
individual, which determines a specific characteristic (phenotype) of that cell/organism/individual.
Genotype is one of three factors that determine phenotype, the other two being inherited epigenetic
factors, and non-inherited environmental factors. DNA mutations which are acquired rather than inherited,
such as cancer mutations, are not part of the individual's genotype.
Phenotype
A phenotype (from Greek phainein, meaning "to show", and typos, meaning "type") is the composite of
an organism's observable characteristics or traits, such as its morphology, development, biochemical or
physiological properties, phenology, behavior, and products of behavior (such as a bird's nest). A
phenotype results from the expression of an organism's genes as well as the influence of environmental
factors and the interactions between the two. When two or more clearly different phenotypes exist in
the same population of a species, the species is called polymorph.

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The Biological Sources of Developmental Disabilities Basic
terms in Human Reproduction
Gametes- are human reproduction cells
which are created in the reproductive
organs.
Ovum- egg cells; which the ovaries of
the female produce
Spermatozoa- sperm cells; which the
testicles/testes of the male produce

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Meiosis
The process of cell division in which each pair of
chromosomes in the cell separates, with one member of each
pair going into each gamete or daughter cell. Thus, each
gamete, the ovum and the sperm, has twenty-three unpaired
chromosomes.

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Fertilization - is the union of a human egg and sperm,
usually occurring in the ampulla of the uterine tube. The
result of this union is the production of a zygote, or
fertilized egg, initiating prenatal development.
zygote- fertilization results in the formation of a single cell.
In the zygote, 2 sets of 23 unpaired chromosomes, one set
each from the male and female combine to form one set of
paired chromosomes. In this manner, each parent
contributes 50% or half of the zygote's genetic code or
genome.

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Critical periods and developmental vulnerability during
pregnancy
Vulnerability- refers to how susceptible the organism is to being
injured or altered by a traumatic accident.
A traumatic incident includes such broad occurrences as teratogens
or toxic agents.
Deviancy - from the normal course of prenatal development
results to the occurrence of developmental disabilities.

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The Course of Prenatal
Development

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Germinal Phase
-the initial stage of prenatal development covers first two
weeks of fertilization.
3 significant developments:
1. Creation of zygote- reproduction begins with the fertilization
of a female's ovum by a male sperm
Ovulation- is when a mature egg is released from the ovary,
pushed down the fallopian tube, and is available to be fertilized.
Approximately every month an egg will mature within one of your
ovaries.

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Fertilization- takes place when the union of the genetic materials in
the ovum and sperm cells.
Zygote- new cell w/c results from the transmission of the genetic
materials 24 to 23 hours after fertilization.
2. Continuous cell division and cell tissue differentiation
Cell division- occurs very rapidly in the first few days and progress with
considerable speed. Cell differentiation- continues as the inner and
outer layers of the organism are formed.

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Blastocyst- inner layer of cells w/c develop the embryo later on
Trophoblast- outer layer of cells that provides nutrition and support
for the embryo.
3. Implantation or attachment of the zygote to the uterine
wall
what can go wrong during the germinal phase?
genetic disorders can be transmitted such as;

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3. Polygenic Inheritances
polygenic inheritance is a fancy term for those genetic
traits that are controlled by more than 1 gene
human skin color involves the interaction of at least 3
genes
skin color variation can be modified by environmental
factors
obesity, autism, cancer, diabetes

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Embryonic Phase
the second phase of human development occurs from the end of the germinal
phase to the second month of pregnancy. The mass of cells is now called the
Embryo.
3 main process during this phase;
intensification of cell differentiation
1.
a. ectoderm - outermost layers of cells that will then be develop into surface
body parts
b. mesoderm - the middle layer that will develop into body parts sorrounding
the internal areas
c. endoderm - the inner most layers of cell that will develop into epithelium

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3. Organogenesis is the process of organ formation and the
apperance of body parts
what can go wrong with the embryonic phase?
physical abnormalities can result at birth, there are
infants who are born with extra or missing limbs, fingers,
ears and other body parts.
a tail-like protrusion, heart or brain, digestive or
respiratory organs or outside the body.

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Fetal Phase
the third phase covers seven months that last
from the third to ninth of preganncy on the
average.

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environmental-causes-of-developmental-disabilities