Genetics, Embryology, and Birth Defects
The development of powerful electron microscopes has enabled the rapid
increase in investigations in genetics* and embryology in the twenty-first
century. Traditionally, geneticists have studied genes and chromosomes,
and embryologists have studied the development of fetuses. However, in
the early 2000s, areas of research combined genetics and embryology to
understand why individuals develop birth defects. Study of the interplay
between genetic and environmental factors of the uterus allowed scientists
to understand these developmental abnormalities in humans.
Genetics In the nucleus* of most cells about six feet of deoxyribonucleic
acid (DNA) are packaged into 23 pairs of chromosomes*, threadlike
structures inside cells on which the genes* are located. Each gene is
a segment of DNA that holds the recipe for making a specific molecule,
usually a protein. These recipes are spelled out in varying sequences of the
four chemical bases in DNA: adenine (A), thymine (T), guanine (G), and
cytosine (C). A is always paired with T; G is always paired with C. The
two are called base pairs. The DNA molecule looks like two ladders with
a side taken off and twisted together; the rungs of the ladders are the base
pairs. Millions of these base pairs can make up a single gene. These genes
direct the growth and characteristics of the organism through the production
of chemical proteins. Proteins are made up of amino acids and
are the essential components of all organs and chemical activities. Their
functions depend on their shape and are determined by the 30,000 genes
in the cell nucleus. The complete makeup of the genes of an individual is
called the genome. Of course, with so many chemical reactions going on,
various problems may develop.
Embryology The origin of the genetic material or DNA that a person
inherits begins in the reproductive systems of parents. Sperm and
egg (ova) or cells, called gametes carrying half of the parent’s genes are
created through a process called meiosis* or reduction division. In this
complex process, the parent cells in the testes (sperm) of the male and
the ovaries of the female (ovum) reduce their DNA by half so that they
can join together and make a fertilized egg that contains one gene from
the mother and one gene from the father. Human body cells or somatic
cells have the full set of 46 chromosomes. However, each gamete has only
half that number, or 23. In males, meiosis takes place in the testicles and
occurs about every 74 hours, beginning at about 12 to 13 years of age
and continuing through life. Millions of sperm are produced daily, but as
many as 20 percent may be defective. A more complex process of meiosis
occurs in females, beginning about the fifth month after conception
when immature ova are formed. The ova remain in the premature form in
the ovaries until hormones signal the release. The egg does not complete
its development until conception when chemical changes occur as the
main part of the sperm enters the ovum. Unlike the male, the female is
born with all the ova she will ever have. At fertilization or conception, the
23 chromosomes of the father and 23 of the mother create a completely
new individual with 46 chromosomes and a unique genetic makeup.
Scientists have come a long way in understanding the development of
the embryo in utero, the Latin term for “in the uterus”. This knowledge
assists their understanding of genetic and birth defects. In the early stages
of development, the fertilized egg (now called a zygote) divides to form a
blastocyst; some of these cells become the three layers of the embryo:
tube reaches the uterus and implants in the uterus. At about 12 days after
conception, a band called the primitive streak appears along the back of
the mass of cells; the neural tube, which develops into the spinal cord
and brain, begins to develop at about this time and continues to develop
throughout pregnancy. At about five weeks the general form of the human
body becomes evident with traces of hands, feet, clavicle, and lower jaw.
During the first 12 weeks of development, the cells of the embryo are
rapidly dividing and becoming muscles, bones, and organs. Although during
the first three months, the embryo is most vulnerable, at any time
during the remaining six months, the fragile fetus is susceptible to many
factors that affect development.
increase in investigations in genetics* and embryology in the twenty-first
century. Traditionally, geneticists have studied genes and chromosomes,
and embryologists have studied the development of fetuses. However, in
the early 2000s, areas of research combined genetics and embryology to
understand why individuals develop birth defects. Study of the interplay
between genetic and environmental factors of the uterus allowed scientists
to understand these developmental abnormalities in humans.
Genetics In the nucleus* of most cells about six feet of deoxyribonucleic
acid (DNA) are packaged into 23 pairs of chromosomes*, threadlike
structures inside cells on which the genes* are located. Each gene is
a segment of DNA that holds the recipe for making a specific molecule,
usually a protein. These recipes are spelled out in varying sequences of the
four chemical bases in DNA: adenine (A), thymine (T), guanine (G), and
cytosine (C). A is always paired with T; G is always paired with C. The
two are called base pairs. The DNA molecule looks like two ladders with
a side taken off and twisted together; the rungs of the ladders are the base
pairs. Millions of these base pairs can make up a single gene. These genes
direct the growth and characteristics of the organism through the production
of chemical proteins. Proteins are made up of amino acids and
are the essential components of all organs and chemical activities. Their
functions depend on their shape and are determined by the 30,000 genes
in the cell nucleus. The complete makeup of the genes of an individual is
called the genome. Of course, with so many chemical reactions going on,
various problems may develop.
Embryology The origin of the genetic material or DNA that a person
inherits begins in the reproductive systems of parents. Sperm and
egg (ova) or cells, called gametes carrying half of the parent’s genes are
created through a process called meiosis* or reduction division. In this
complex process, the parent cells in the testes (sperm) of the male and
the ovaries of the female (ovum) reduce their DNA by half so that they
can join together and make a fertilized egg that contains one gene from
the mother and one gene from the father. Human body cells or somatic
cells have the full set of 46 chromosomes. However, each gamete has only
half that number, or 23. In males, meiosis takes place in the testicles and
occurs about every 74 hours, beginning at about 12 to 13 years of age
and continuing through life. Millions of sperm are produced daily, but as
many as 20 percent may be defective. A more complex process of meiosis
occurs in females, beginning about the fifth month after conception
when immature ova are formed. The ova remain in the premature form in
the ovaries until hormones signal the release. The egg does not complete
its development until conception when chemical changes occur as the
main part of the sperm enters the ovum. Unlike the male, the female is
born with all the ova she will ever have. At fertilization or conception, the
23 chromosomes of the father and 23 of the mother create a completely
new individual with 46 chromosomes and a unique genetic makeup.
Scientists have come a long way in understanding the development of
the embryo in utero, the Latin term for “in the uterus”. This knowledge
assists their understanding of genetic and birth defects. In the early stages
of development, the fertilized egg (now called a zygote) divides to form a
blastocyst; some of these cells become the three layers of the embryo:
- Ectoderm: the outer layer that gives rise to the hair, nails, skin,
sense organs, brain, and spinal cord - Mesoderm: the middle layer that gives rise to bones, muscles, circulatory
and most of the reproductive organs - Endoderm: the inner layer that eventually links the body cavity, the
respiratory system, digestive tract, and many glands
tube reaches the uterus and implants in the uterus. At about 12 days after
conception, a band called the primitive streak appears along the back of
the mass of cells; the neural tube, which develops into the spinal cord
and brain, begins to develop at about this time and continues to develop
throughout pregnancy. At about five weeks the general form of the human
body becomes evident with traces of hands, feet, clavicle, and lower jaw.
During the first 12 weeks of development, the cells of the embryo are
rapidly dividing and becoming muscles, bones, and organs. Although during
the first three months, the embryo is most vulnerable, at any time
during the remaining six months, the fragile fetus is susceptible to many
factors that affect development.
0 Response to "Genetics, Embryology, and Birth Defects"
Post a Comment