Biological and Environmental Causes of Developmental Disabilities
Biological and Environmental Causes of Developmental Disabilities
Biological and Environmental Causes of Developmental Disabilities
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.
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.
DNA
Gene – specific sequence of the four
nucleotide bases whose sequences
carry the information for constructing
proteins.
Some Principles of
Genetic
Determination
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. (66)
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.
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.
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.
Genetoype
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.
The Biological Sources of
Developmental
Disabilities
Basic terms in Human Reproduction
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.
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.
Caucasian baby
At 3 months, the fetus is about 3 inches long
and weighs about one ounce.
At 4 months, the fetus is five and a half
inches long. Weighing about four ounces.
At 5 months, the fetus is ten to twelve inches
long and weighs one half to one pound or
almost half a kilo.
At six months, the fetus is 14 inches long and
has gained one half to one pound.