This document summarizes key concepts in human reproduction including heredity, chromosomes, DNA, genes, genetic principles of dominance-recessive and sex-linked genes. It describes meiosis, fertilization which results in a zygote, and the three phases of prenatal development: germinal phase involving cell division and implantation; embryonic phase of cell differentiation and organogenesis; and fetal phase of growth over seven months. Critical periods of vulnerability to teratogens are noted where genetic disorders, physical abnormalities or developmental disabilities can occur.

1. Chapter 4
By: Mrose 

2. The 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.

4.  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.

5. DNA

6.  Gene – specific sequence of the four
nucleotide bases whose sequences
carry the information for constructing
proteins.

7. Some Principles of
Genetic
Determination

8. 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)

10. 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.

12. 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.

14. 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.

15. 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.

17. 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

19. 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.

20.  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.

21. zygote

23. 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.

24. The Course of Prenatal
Development

25. GERMINAL PHASE
-the initial stage of prenatal development
covers first two weeks after fertilization.
3 significant developments :
1. Creation of zygote- reproduction begins
with the fertilization of a female’s ovum
by a male sperm

26. 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.

27. 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.

28. Blastocyst- inner layer of cells w/c develop into
the embryo later on
Trophoblast- outer layer of cells that provides
nutrition and support for the embryo.

29. 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:

30. 1. Dominant and recessive diseases like:

31. Genetic mutation

32. 2. Sex-linked inheritances such as:

34. 3. Polygenic inheritances

35. 4. Chromosomal deviations

36. 5. Sex chromosomal anomalies like:
Klinefelter syndrome

37. 6. Cranial or skull malformations such as:

38. significant developments in the
germinal period

39. 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 :
1. Intensification of cell differentiation
a. ectoderm –outermost layer of cells that
will develop into the surface body parts

40. b. mesoderm- the middle layer that will develop
into the body parts surrounding the internal
areas
c. endoderm- the inner layer of cells that will
develop into the epithelium

41. 2. Development of the life support systems

42. 3. Organogenesis – is the process of organ
formation and the appearance of body organs
during the first two months.
What can go wrong during the embryonic phase?
Physical abnormalities can result. At birth,
there are infants born with extra or missing
limbs and fingers, ears and other body parts, a
tail-like protrusion, heart or brain, digestive or
respiratory organs outside the body.

44. Fetal Phase
 The third phase covers seven months that
lasts from the third to ninth month of
pregnancy on the average.
Caucasian baby

45.  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.