Mechanisms of Genetic
Transmission
 Genetic information is combined and
transmitted by gametes, the reproductive
cells of a child’s parent
 In the father the gametes are produced in
the testicles (each is called a sperm cell)
 In the mother they are developed in the
ovaries (each is called an ovum or egg cell)
Mechanisms of Genetic
Transmission (continued)
 The sperm and egg cells contain genetic
information molecular structure called
genes
 The genes form threads called
chromosomes
 Genetic material that the child will inherit
from the parent is contained in the
chromosomes
Mechanisms of Genetic
Transmission (continued)
 Each human sperm or egg cell contains 23
chromosomes
 All other cells of the body contain 46
chromosomes and about 100,000 genes
 A single chromosome may contain as many
as 20,000 genes
DNA
 The genes are made up of DNA
(deoxyribonucleic acid)
 DNA have a spiral chemical structure that
allows them to divide easily and duplicate
DNA molecules
 DNA contains the genetic information that
directs the form and function of each body
cell as it develops
DNA (continued)
 DNA is shared at conception when a sperm
(father) penetrates the egg from the mother
 Within a few hours the walls of the sperm
cell and the nucleus of the egg cell both
begin to disintegrate releasing its
chromosomes which join to form a new cell
 The new cell formed is called a zygote
Meiosis and Mitosis
 All cells of the body develop from this
original zygote through a process called cell
division
 The sperm and ova contains only 23
chromosomes making them unique from
other body cells
 This ensures that when an egg and sperm join
to form a new zygote the zygote will contain
the complete set of 46 chromosomes (23 pair)
The human
body
contains
100 trillion
cells.
There is a
nucleus inside
each human
cell (except red
blood cells).
Each nucleus
contains 46
chromosomes,
arranged in
23 pairs.
One
chromosome
of every pair is
from each
parent.
The
chromosomes
are filled with
tightly coiled
strands of
DNA.
Genes are
segments
of DNA that contain
instructions to make
proteins— the
building blocks
of life.
Meiosis and Mitosis (continued)
 The zygote contain the genetic materials
from which all of an individual’s cells are
formed
 The reproductive cells (gametes) divide by a
process called meiosis and recombine into a
zygote at conception
 All other cells will develop from the zygote
through a simpler division called mitosis
Meiosis and Mitosis (continued)
 Mitosis involves:
 1. 23 pairs of chromosomes of a cell
duplicate themselves and divide into two
identical sets
 2. The two sets of chromosomes move to
opposite sides of the cell
 3. A new wall forms between them, resulting
in two new identical cells containing the
same set of chromosomes, genes and DNA
Gametes and Zygote
Sperm
Sperm
Ovum
Gametes
(reproductive cells)
Fertilization
Zygote
The Process of Meiosis for Sperm Cells
Cell with 46 chromosomes
(only one pair of
homologous
chromosomes is shown
here). Each member of the
pair has begun to replicate
similar to
mitotic cell division.
First meiotic cell division
begins, but does not proceed
as in mitosis. Instead of the
replicated chromosome splitting
apart, one member of each
homologous pair becomes a
part of the first-generation
daughter cell.
The second meiotic division
proceeds after the first is completed;
now the replicated chromosome
acquired in the first-generation
daughter cell splits apart.
Each of the four gametes
produced by the two-step process
now has acquired one member
of the pair of homologous
chromosomes.
The Process of Mitosis
Cell nucleus with a pair
of chromosomes
Chromosomes split
and replicate to produce
two identical pairs
The pairs separate,
and the cell divides
Each daughter cell
now has a pair of
chromosomes that is
identical to the
original pair
GENOTYPE AND PHENOTYPE
 GENOTYPE: Set of genetic traits a
person inherits; a person’s inborn
capacity or potential
 PHENOTYPE: Set of traits a person
actually displays, resulting from a
combination of the person’s genotype
(potential) and life experiences that
modify that potential
Individual Genetic Expression
(continued)
 Examples of phenotype may include a
certain height, intelligence score, shyness
 Phenotype results from all the interactions
of the person’s genotype with the
environment from conception onward
Genes (dominant and recessive)
 Genes are inherited in pairs (one from each
parent)
 Dominant gene--in a paired set of genes,
the gene with the greater influence in
determining physical characteristics
 Recessive gene--in a paired set of genes,
the gene that influences or determining
physical characteristics only when no
dominant gene is present
Genes (dominant and recessive)
continued
 A dominant gene will influence a child’s
phenotype even if it is paired with a
recessive gene
 A recessive gene must be paired with
another recessive gene to be able to
influence the phenotype
 If paired with a dominant gene its influence
is blocked
Genes (dominant and recessive)
continued
 Eye color--blue eyes (recessive trait), brown
eyes (dominant trait)
 a child’s eyes will remain blue only if they
have received the appropriate blueproducing gene from both parents
 If they received it from only one parent or
from neither they will end up with brown
eyes (dominant)
Genes (dominant and recessive)
continued
 Genes may take on two or more alternatives
forms called alleles
 a person who inherits two identical alleles
for a particular trait is homozygous for that
trait
 if they inherit two different alleles for the
trait it is heterozygous
Polygenic
 Blood type and eye color have a limited
number of distinct ways of transmission
 height, weight, skin color, personality,
behavioral traits are polygenic (involve
many genes)
 Environment influence them in important
ways (can diet and change weight)
Determination of Sex
 One pair of chromosomes among the 23 is
largely responsible for determining whether
a child is male or female
 In women the pair of chromosomes is XX
 In men the pair is XY
 all eggs cells contain a single X chromosome
 a sperm cell may contain either an X or Y
Determination of Sex (continued)
 If a Y bearing sperm fertilizes the egg, a
male (XY) zygote develops
 If a X bearing sperm fertilizes the egg a
female (XX) zygote develops
Genetic Abnormalities
 Sometime too many or too few
chromosomes transfer (or transfer a
defective gene) to newly forming zygote
 This may affect a child mentally, physically
or both
 Inheriting too many or too few
chromosomes is usually fatal
Genetic Abnormalities (continued)
 In a few cases children with a missing or an
extra chromosome survive
 Down syndrome--caused by extra 21st
chromosome or transfer or part of the 21st
on to another chromosome
Genetic Abnormalities (continued)







Characteristics of Down’s Syndrome
almond shaped eyes, round head
stubby hands and feet
may have abnormal heart and intestinal tract
facial deformities
vulnerable to diseases such as leukemia
as they age fall behind developmentally
Genetic Abnormalities (continued)
 Usually levels out at the moderately
retarded level
 most live until middle adulthood
 they are able to do simple routines and hold
these type of jobs
 more frequent in mothers over the age of 35
FREQUENCY OF DOWN SYNDROME (PER 1000)
Relationship Between Maternal Age and
the Incidence of Down Syndrome
100
90
80
70
60
50
40
30
20
10
0
15
20
25
30
35
40
MATERNAL AGE (YEARS)
45
50
Pictures of Down’s syndrome
individuals
Down Picture #2
An adult Down’s person
Genetic Abnormalities (continued)
 Klinefelter Syndrome- results from inheriting an extra chromosome
(usually an X) resulting in an XXY pattern
 affects males (they are sterile, have small
testes)
 have normal intelligence
 affect about 1/800
Klinefelter Syndrome is caused by a chromosome variation
involving the sex chromosomes. The person with Klinefelter
Syndrome is a male who, because of this chromosome variation,
has a hormone imbalance. While Dr. Harry Klinefelter accurately
described this condition in 1942, it was not until 1956 that
other researchers reported that many boys with this description
had 47 chromosomes in each cell of their bodies instead of the
usual number of 46. This extra sex (X) chromosome causes the
distinctive make-up of these boys. All men have one X
chromosome and one Y chromosome, but sometimes a variation
will result in a male with an extra X. This is Klinefelter Syndrome
and is often written as 47,XXY. There are other, less common
variations such as 48,XXYY; 48,XXXY; 49,XXXXY ; and
XY/XXY mosaic. All of these are considered Klinefelter
Syndrome variants.
Klinefelter Karotype
Klinefelter individual
Genetic Abnormalities (continued)
 Turner syndrome- results from having only one sex
chromosome (X0) affecting females
 will develop learning disabilities
 not fully sexually differentiated
 are very short as adults (4 and 5 ft.)
 have webbed necks
 ears are set lower than usual
Adults with Turner syndrome are short, averaging around four
feet, eight inches in height. But girls with Turner syndrome
don't start life as very short individuals - they become short over
time, growing more slowly than their sisters and friends
with each passing year. Studies have shown that a medicine
called recombinant human growth hormone, or GH, can
improve the height of girls with Turner syndrome. However,
these studies have tended to start GH treatment around age 9
or later, after years of deteriorating growth. So, even with
treatment, many girls remain shorter than would be expected
based on the heights of their parents. The purpose of this new
study is to determine if GH started at a young age can
prevent the growth failure typical of girls with Turner syndrome.
In addition, the study will monitor all participants for
development of ear infections and hearing loss, problems that
trouble many girls with Turner syndrome.
A Turner’s syndrome infant
A Turner’s syndrome teen
Disorders from Abnormal Genes





Three types of genetic disorders:
1. dominant gene disorder
2. recessive gene disorder
3. multifactorial gene disorder
Dominant gene disorder require only one
abnormal gene from either parent to affect a
child
Disorders from Abnormal Genes
(continued)
 Huntington disease (dominant gene
disorder)
 gradual deterioration of the central nervous
system, causing mental retardation and
uncontrollable movements
 appear when person is in their 30’s or 40’s
 always fatal
Disorders from Abnormal Genes
(continued)
 Recessive gene disorder- can occur when the fetus inherits a pair of
recessive genes, one from each parent
 Cystic Fibrosis--involves production of
thick mucus, clogging the lungs
 causes delayed growth and sexual
maturation, shortened life and vulnerable to
infections
Disorders from Abnormal Genes
(continued)
 Sickle-Cell Disease--red blood cells take on
a sickle shape instead of a round shape
 These cells get caught in the blood vessels
cutting off circulation, reducing oxygen
supply causing pain
 have bacterial infections
 degeneration of organs (due to lack of
oxygen)
 few live past 40 years of age
Disorders from Abnormal Genes
(continued)
 Tay-Sachs Disease--disease of the nervous
system (chemical imbalance)
 about age 6 months will show poor tolerance
for sudden loud noises, seem weak and slow
to develop
 lead to seizures, deafness and blindness
 most die by age 3
Disorders from Abnormal Genes
(continued)
 Phenylketonuria (PKU)--occurs in 510/1000, inability to utilize an amino acid
called phenylalanine (found in milk, meat)
and needed for normal growth
 increases in levels of phenylalanine in the
blood and spinal fluid affects the brain
causing deterioration of cognitive
functioning and mental retardation
Disorders from Abnormal Genes
(continued)
 Multifactorial disorders- result from a combination of genetic and
environmental factors
 Neural tube defects--result when the tube
enclosing the spinal cord fails to close
completely or normally
 Sometimes the upper part of the brain is
absent or underdeveloped
Disorders from Abnormal Genes
(continued)
 Causes include heredity and environmental
aspects such as pollutants, poor nutrition,
diseases (diabetes)
 geographical background and racial/ethic
background)
 British Isles has the highest
 U.S. highest is in the the Appalachian region
Disorders from Abnormal Genes
(continued)
 Cleft palate/lip--when the upper lip and/or
roof of the mouth fail to grow resulting in a
split or “cleft”
 If severe may lead to difficulties breathing,
speaking, hearing and eating
 surgery can usually repair the problem
Disorders from Abnormal Genes
(continued)
 Congenital heart disease--structural and/or
electrical abnormalities in the formation of
the heart
 medication and surgery can usual correct
Prenatal Diagnostic Techniques
 Diagnostic techniques after conception but
before birth
 Ultrasound--high frequency sound waves
are projected through the mother’s womb
 Waves bounce off the fetus creating a
television image of the size, shape, and
position of the fetus
Prenatal Diagnostic Techniques
(continued)





Ultrasound can be used to:
determine age of fetus
multiple pregnancies
physical defects in internal/external organs
determine Down’s Syndrome (extra fold of
skin on the neck)
Prenatal Diagnostic Techniques
 Amniocentesis--performed at weeks 14-18
 Using, ultrasound a slender needle is inserted
through the mother’s abdomen into the
uterus and the amniotic sac and a sample of
amniotic fluid is withdrawn
 Fluid contain the cells which hold the genetic
makeup of the fetus
 can be used to determine if they have
abnormal chromosomes
Prenatal Diagnostic Techniques
(continued)
 Amniocentesis
 It can also determine disorders such as
Down’s Syndrome, neural tube defect and
sex of the baby
Prenatal Diagnostic Techniques
(continued)
 Chorionic Villus Sampling (CVS)
 tests for most of the same disorders as
amniocentesis does
 performed between the 8th & 10th week of
pregnancy
 involves collecting and analyzing tissue by
inserting a catheter through the vagina into
the uterus between the uterine lining and the
chorion (surrounds the embryo, becomes the
placenta later)
Prenatal Diagnostic Techniques
(continued)
 This technique lets parents know very early
whether the fetus has inherited any serious
defects
 primary risk of procedure is miscarriage
 Fetoscopy--inserting a fetoscope (telesopic
type fiber optic lens through the abdomen
into the uterus to observe the amniotic fluid,
placenta, and fetus
 performed 15th-18th week
Prenatal Diagnostic Techniques
(continued)
 Fetoscopy is used to observe already
identified problems or to confirm other
prenatal tests
 Maternal Serum Alpha Fetoprotein
 test measuring the amount of alphafetoprotein (AFP) in the mother’s blood
 performed 15th-18th week
 fetoprotein is produced by the fetus and
passes from the amniotic fluid through the
placenta into the mother’s bloodstream
Prenatal Diagnostic Techniques
(continued)
 High level of AFP are associated with
various problems as anencephaly (lacking a
brain), spina bifida, and Down’s Syndrome
 Percutaneous Umbilical Blood Sampling
(PUBS)
 experimental method of sampling fetal blood
by guiding a needle through the mother’s
abdomen and uterus and umbilical vein
 performed between the 18th and 36th week
Prenatal Diagnostic Techniques
(continued)
 Used to diagnosis numerous conditions, such
as Down Syndrome, neural tube defects,
cystic fibrosis)
Risk of Selected Genetic Disorders
Chromosomal
Down Syndrome
Klinefelter syndrome (XXY)
Fragile X syndrome
Turner syndrome (XO)
Dominant Gene
Polydactyly
Achondroplasia
Huntington disease
Recessive Gene
Cystic fibrosis
Sickle-cell disease
Tay-Sachs disease
1/800
1/800 men
1/1,200 male births
1/2,000 female births
1/3,00 women
1/300 - 1/100
1/2,300
1/15,000 - 1/5,000
1/2,500 white persons (risk of being a carrier is 1/25)
1/625 African Americans (risk of being a carrier is 1/10)
1/3,600 Eastern European Jews(risk of being a carrier is 1/30 1/300)
X Linked
Hemophilia
1/2,500 male babies
Multifactorial
Congenital heart disease
Neural tube defect
Cleft lip/cleft palate
1/125
1 - 2/1,000
1/1,000 - 1/5,000
Sources: ACOG (1990); Blatt (1988); Diamond (1989(; Hagerman (1996); Selekman (1993); Stratford (1994).
Who Should Seek Prenatal Counseling?
1. Couples who already have a child with some serious defect such as Down
syndrome, spina bifida, congenital heart disease, limb malformation, or
mental retardation
2. Couples with a family history of a genetic disease or mental retardation
3. Couples who are blood relatives (first or second cousins)
4. African Americans, Ashkenzzi Jews, Italians, Greeks, and other high-risk
ethnic groups
5. Women who have had a serious infection early in pregnancy (rubella or
toxoplasmosis) or who have been infected with HIV
6. Women who have taken potentially harmful medications early in
pregnancy or habitually use drugs or alcohol
7. Women who have had X rays taken early in pregnancy
8. Women who have experienced two or more of the following: stillbirth,
death of a newborn baby, miscarriage
9. Any woman thirty-five years or older
Source: Adapted from Fienbloom & Forman (1987) p. 129
Behavior Genetics
 Behavior genetics--is the study of how
genetic inheritance (genotype) and
environmental experience jointly influence
physical and behavioral development
(phenotype)
Behavior Genetics (continued)
 Four concepts of behavior genetics
 range of reaction-the range of possible
phenotypes that an individual with a
particular genotype might exhibit in
response to the specific sequence of
environmental influences they experience
 influences as neighborhood, child’s family,
school and community etc.
Behavior Genetics (continued)
 Canalization--tendency of genes to
narrowly restrict the development of certain
phenotypic characteristics to a single or
relatively limited number of outcomes in
spite of environmental pressures toward
other outcomes
 early perceptual-motor (crawling, sitting up
are canalized)
Behavior Genetics (continued)
 Others include personality, temperament,
intellectual functioning
 Gene-Environment Relationship patterns of interaction between a newborn
infant and his caregiving environment and
the extent to which that pattern supports the
expression and development of the child’s
inborn traits
Behavior Genetics (continued)




Examples include:
shyness
athletic ability
parents may display their own genetically
inherited traits that support the development
of similar traits in their children
Behavior Genetics (continued)
 A passive gene-environment relationship if support for the development of traits
come from others (parents and family
members)
 Evocative gene-environment relationship displayed by child of certain traits evokes
support from others
Behavior Genetics (continued)
 Active gene-environment relationship- when a child with a particular trait actively
seeks out support from others with similar
traits (sports, etc.)