NOTES AND TEST
Beginning of Life : 23 pairs of
chromosomes
1. Mechanisms of heredity
a.
Humans have 23 pairs of chromosomes, of which 22 pairs are the
autosomes plus the sex chromosomes
b. Genotype
– is the actual set of genes an individual inherits.
Phenotype –
refers to the genes that are expressed. The result of the
interaction of the genotype and the environment
c.
Alleles – are different forms of the same gene.
Homozygous – a
person who inherits the same allele on a pair of chromosomes. The
biochemical instructions on the allele are followed
Heterozygous –
a person who inherits different alleles on a pair of chromosomes.
The biochemical instructions of the dominant allele are followed
whereas those instructions of the recessive allele are ignored.
A number of behavioral and psychological phenotypes (intelligence,
extroversion, introversion) involve differences along an
underlying continuum. These phenotypes involve polygenic
inheritance, and the phenotype reflects the combined activity of
a number of distinct genes. The influence of heredity and
environment is revealed by studying twins and adopted children
2. Genetic Disorders
a. Genetic disorders – the result of inheriting harmful genes, usually recessive resulting in diseases such as PKU
b.
Genetic disorders can also result because an extra, a missing or
a damaged chromosome. Most of the fertilized eggs that do
not have 46 chromosomes – 44 autosomes and 2 sex chromosomes-
are spontaneously aborted soon after conception. One
exception is Down syndrome, in which the individual has and extra
21st chromosome. Individuals with Down syndrome
have a distinctive appearance and are mentally retarded.
c.
Genetic disorders can also result because an extra, a missing or
a damaged chromosome. Most of the fertilized eggs that do
not have 46 chromosomes – 44 autosomes and 2 sex chromosomes-
are spontaneously aborted soon after conception. One
exception is Down syndrome, in which the individual has and extra
21st chromosome. Individuals with Down syndrome
have a distinctive appearance and are mentally retarded.
d.
More common are disorders of the sex chromosomes, because these
chromosomes contain less genetic material. One of those
disorders is Klinefelter’s syndrome, Turner’s syndrome,
XYY complement, and XXX syndrome
3. Genes and Environment
a.
PKU - is an inherited disorder. Phenylalanine
accumulates in the body, and damages the nervous system. The
result is mental retardation, which can be avoided with a diet
that is low in phenylalanine. PKU demonstrates the
concept of reaction range, which is the outcome of heredity
depends upon the environment in which the development occurs
b.
Heredity can have an influence on the types of experiences
children have. Individuals usually seek environments that
fit their genotype, this process is known as niche-picking.
4.
From Conception to Birth
a.
Period of the Zygote
This period begins with the fertilization of the egg by the sperm and ends when the zygote is implanted in the wall of the uterus, usually about two weeks after conception.
b.
Period of the Embryo
During this period
there is rapid growth, and most of the major body structures are
created. It ends at 8 weeks after conception
c. Period of the Fetus
This period last
until birth. The fetus becomes much larger and the majority
of the systems of the body that are necessary for life begin to
function
5.
Influences on Prenatal Development
a.
General Risk Factors
Maternal age,
maternal nutrition, amount of stress the mother experiences
during her pregnancy
b.
Teratogens: Drugs, Disease and Environmental hazards
Exposure to
teratogens can cause prenatal development to go wrong. Major
categories of teratogens include drugs (alcohol, cocaine, heroin,
etc), diseases (AIDS, rubella) and finally environmental hazards
(PCBs and x-rays)
c.
Influence of teratogens in prenatal development
The impact that a
teratogens will have greatly depends upon the genotype of the
organism, the period of prenatal development when the organism
was exposed, and the amount of exposure. Teratogens usually
affect a specific aspect of prenatal development and sometimes
the impact they have is not evident until later in life
6.
Prenatal Diagnosis and Treatment
Medical procedures that help determine if prenatal development is progressing normally include utltrasound, amniocentisis and chorionic villus sampling
7.
Labor and Delivery
a.
Stages of Labor
Labor consists of
three stages: the initial phase in which the cervix enlarges, the
baby’s birth, and the delivery of the placenta
b.
Approaches to Childbirth
A number of women
prefer natural childbirth; one of the aims of this approach is to
reduce labor pain by relaxing (Lamaze method). Today in the
U.S. the majority of the babies are born in hospitals, however
some couples choose to give birth at home or in a birth center
c.
Birth Complications
One birth
complication is that some newborns experience lack of oxygen
because the umbilical cord is pinched closed during delivery or
because their lungs do not work.
Another one happens
when babies are born prematurely or with low birth weight. Those
babies usually lag behind the babies that were born full-term
during the first year, but soon catch up.
Newborns with low
birth weight can develop normally if they have excellent medical
care and a supportive environment, but babies with very low or
extremely low birth weight usually do not fare well
8.
Infant Mortality
The infant
mortality in the United States is quite high, with 9 infants out
of 1000 living less than one year. This high rate is the
result of the high incidence of low birth weight babies.