Chapter 3

pumpkincentersulkyBiotechnologie

16 déc. 2012 (il y a 4 années et 10 mois)

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Forming a New Life

Chapter 3




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Genetic Testing and Engineering


Genomics

the study of functions and
interactions of various genes


Genetic testing:

Should children be
tested?



Would you want to know if you were
predisposed for a particular disease?


Are there potential ethical and moral issues
with genetic testing?


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Guideposts for Study


How does conception normally occur, and what
causes multiple births?


How does heredity operate in determining sex
and transmitting normal and abnormal traits?


How do scientists study the relative influences of
heredity and environment, and how do heredity
and environment work together?


What roles do heredity and environment play in
physical health, intelligence, and personality?


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Guideposts for Study


What are the three stages of prenatal
development, and what happens during
each stage?


What environmental influences can
affect prenatal development?


What techniques can assess a fetus

s
health, and why is prenatal care
important?


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Conceiving New Life


Fertilization


Union of sperm and ovum to produce a
single
-
celled zygote


Also called conception


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Two Types of Multiple Births


Monozygotic (MZ)


One egg


One sperm


Identical twins


Share 100% of genes


Dizygotic (DZ)


Two eggs


Two sperm


More common


Fraternal twins


Share 50% of genes


just like non
-
twin siblings


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Rise in Multiple Birth Rate


Factors


Rising trend toward delaying childbirth


Increasing use of fertility drugs


Related Risks


Pregnancy complications


Premature delivery and lower birth weight


Infant disability or death


Chromosome (DNA molecule)

-

Long strands of genes


Humans have 22 pairs
autosomes and one pair of
sex chromosomes (for a total
of 46)


Gene

-

A region of a chromosome


It makes a specific protein that affects
one or more hereditary
characteristics


Chromosomes and Genes



Genes
affect every aspect of human behavior, including social




and
cognitive behavior


What is so important about proteins?


Genes are made of Proteins


Proteins
makes up nearly 17 percent of total body weight.


Almost everything is a protein.


Basic structural molecule of all the tissues in the body (cell walls,
blood vessels, etc.).


Major components in neurotransmitters, enzymes,
hormones, antibodies, and in determining eye, hair, and
skin color
.

9


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Determination of Sex



Autosomes
:



22
pairs not related to
sexual expression



Sex
chromosomes:


1 pair determining sex


XX = female


XY = male



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Trait Inheritance


Alleles


Homozygous:

Identical copies of gene


Heterozygous:

Different copies of gene


Polygenic inheritance


Interaction of several genes for a trait


Most traits


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Dominant
-
Recessive Inheritance:

Tongue Curling Example

I


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Gene Expression


Genotype


Actual genetic makeup or allele combinations


Tongue curling ability: DD or Dd


Phenotype


Observable expression of genetic makeup


Product of the genotype


Multifactorial transmission


Experience modifies the expression of a genotype


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Epigenesis


Epigenetic framework or chemical molecules
that alter the way a cell

reads


the gene

s
DNA


Epigenetic markers may contribute to cancer,
diabetes or heart disease


Epigenetic markers may change due to
environment factors


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Inherited Defects


Dominant abnormal
gene


Abnormality inherited from 1 parent


D
-
r or D
-
D

have abnormality, r
-
r does not


1,800 known
disorders (
text
-

p. 62
)


Recessive abnormal gene


Abnormality inherited from both parents


D
-
D has abnormality, D
-
r or r
-
r do not


Incomplete
: Partial dominance


Trait is not fully
expressed



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Sex
-
Linked Inheritance


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Sex
-
Linked Defects


Disorders linked to genes on sex
chromosomes


Red/green color blindness, hemophilia


Affects males and females differently


Carrier


Individual unaffected by disorder but
passes on gene to offspring

Chromosomal Abnormalities


Errors in cell
division shortly after conception


NOT known to be caused by external factors


Types:


Numerical Abnormalities

-

missing or (usually) extra
chromosomes.
NOT
inherited
.


Structural Abnormalities



missing, duplicated, or
mis
-
located genes. Can be inherited.


A factor that most often correlates with chromosomal
abnormalities is the age of the
mother


Examples
-

See text
p.
64


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Numerical
Chromosomal
Abnormalities


Down Syndrome (Trisomy 21)


Individual has 3 copies of chromosome 21 rather
than 2.


Occurs
in about 1 in 740 newborns.


Responsible for 40% of moderate to severe
mental
retardation


People with Down syndrome may be born with a
variety of birth defects.


About
half of all affected children have a heart
defect
.


Translocation Down syndrome
is extremely rare
and is the only form of Down syndrome that
appears to be
inherited.

Numerical Chromosomal
Abnormalities
-

Females


Turner Syndrome


A female is born with only 1 functioning X chromosome.


Short height, wide neck, incomplete development at puberty, infertility


N
ormal life when monitored by their doctor.


Extra X syndrome (
3 X most common)


A female is born with 3


5 X chromosomes


Taller than average, but otherwise normal


More
Xs

increases risk of learning disabilities and
delayed development of speech and language skills
and of motor skills.

Numerical Chromosomal
Abnormalities
-

Males


XYY Syndrome


A male is born with an extra Y chromosome


Taller than average, acne, but otherwise normal


Klinefelter

syndrome (XXY)


A male is born with an extra X chromosome


Taller than average, breasts, reduced secondary sexual
characteristics, infertility


Normal life when monitored by their doctor
.


Variants of
these
syndromes have extra
Xs

or
Ys


A
ssociated
with intellectual disability, distinctive facial features,
skeletal abnormalities, poor coordination, and severe problems
with speech.



Strructural Chromosomal
Abnormalities


Fragile X Syndrome


The FMR1 gene on the X chromosome mutates and
repeats many times


Fragile X syndrome is inherited


Second most common identifiable cause of genetic mental
retardation after Down Syndrome


Males are usually more severely affected by this disorder
than females.


Impairment can range from near normal to learning
disabilities to severe intellectual disability (mental
retardation)


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Genetic Counseling


Helps prospective parents assess risk of
bearing a child with a genetic defect


Karyotype chart shows chromosomal
abnormalities


Especially helpful when:



Already have biological children with defect


Family history


Ethnicity


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Behavioral Genetics


How does heredity and
environment influence traits?


Heritability:


Statistical estimate of heritable
influence on trait variance in a
population


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Measuring Heritability


Family Studies


The degree to which bio
-
relatives share traits


Adoption Studies


The degree to which adopted children resemble
biological relatives or adopted family members


Twin Studies


Concordance:

The degree to which MZ and DZ
twins resemble each other for a trait


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Heredity & Environment:

Working Together


Reaction Range:

Potential variation
in a trait


Canalization:

Heritable restrictions
on the range of trait development


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Intelligence and Reaction Range


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Genotype
-
Environment (G x E)
Correlations


Environment reflects or reinforces genetic
differences


Passive:

Parents provide environment that
fosters trait


Reactive or evocative:

Based on their traits,
children evoke different responses from others


Active or niche picking:

choosing an
environment that suits your traits


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Nonshared Environment


Development reflects unique
environment in which each
child grows up


Accidents


Illnesses


Unique interactions with
friends or peers


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Traits Influenced by

Heredity & Environment


Obesity


Intelligence, school achievement


Personality


Schizophrenia
-

maybe

Fertility


According to the American Society of Reproductive
Medicine


one
-
third of infertility cases are female factor infertility


one
-
third are male factor


one
-
third involve problems on both sides or unexplained


Smoking is a major environmental factor influencing


Women

s fertility


Men

s fertility


Health of


unborn child


unborn child

s children


31

Smoking and fertility


Her eggs are dying, reducing her chances of
conceiving by 10
-
40% per cycle


Some of her eggs have chromosome abnormalities


Damage is not reversible


She will reach menopause 10+ years ahead of her
non
-
smoking friends

32

Sexy?


-

It depends


His sperm count is low and most are malformed


His chances of having a male child are getting lower


Damage is reversible if he stops smoking


Smoking and fertility
-

Women


Nicotine has disruptive effects on egg maturation,
ovulation rates, and fertilization rates, and is
associated with egg chromosome abnormalities


Women who smoke take longer to conceive


Chances of conceiving fall by 10
-
40% per cycle (death
of eggs in the ovaries)


Even low levels of smoking can have a significant
impact


Both active and passive smoking delay conception


Among pill
-
users who smoke
-

the risk of a heart
attack is 20 times higher than non
-
smokers


33

Smoking and fertility


Smoking reduces the quality of semen, lowers sperm
count, and produces malformed sperm


Damage may result in more couples having baby
girls than boys because sperm cells carrying the Y
chromosome are more vulnerable to the toxins in
cigarette smoke


Evidence indicates smoking may cause male sexual
impotence


2X higher than nonsmokers


Smoking increases the risk of impotence by around 50% for
men in their 30s and 40s


34

Effects of smoking may be passed
down through generations


Children's Health Study @ University of Southern
California


Studied parents or guardians of 908 school
-
age children


Children of women who smoked while pregnant were 1.5 times
as likely to develop asthma compared to children of nonsmokers


If the child

s mother and grandmother smoked during
pregnancy, risk increased to 2.6 times


Most surprising, even when a mother did not smoke while she
was pregnant … her child had nearly double the risk of
developing asthma as a child from a smoke
-
free home if the
child

s grandmother smoked during pregnancy

35

Conception


When a sperm penetrates an egg, changes occur in
the protein coating around it to prevent other sperm
from entering the egg.


Gametes (sperm & egg) fuse to become a zygote


Detecting Pregnancy


Human Chorionic
Gonadotrophin

(
hCG
)


Present in blood from the time of conception


Usually takes 3 to 4weeks from the first day of last period
for the levels of
hCG

to be high enough to be detected by
pregnancy tests.




36

Periods of prenatal development


Germinal Period (0
-
2 weeks)


Embryonic Period (2
-
8 weeks)


Fetal Period (9 weeks
-
birth)



Months 4
-
6




Months 7
-
9


37

1
st

trimester

2
nd

trimester

3
rd

trimester

Germinal Stage Development

outside

inside



Zygote
divides into multiple
cells (the blastocyst)
that take on
distinct characteristics and move toward particular
positions.

Blastocyst just before
implantation



Outer
layer of blastocyst becomes outer layer of
placenta

Embryonic Stage Characteristics


Organs and major body systems develop
rapidly


Respiratory,
Digestive, Nervous


Over 90% of the 4500 designated structures of
the adult body are established


This pregnancy phase is very vulnerable


Structural deformities are produced most often
during this time


Ends when the first bone cells appear


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Development During Fetal Stage


Organs and body become
bigger and
more
complex



Finishing Touches

added


toenails,
eyelids


Brain development is
significant
between
10 and 26 weeks after
conception


Age of viability occurs around 22
weeks

Preparing to Survive


Age of viability


22 weeks after conception a fetus
can survive outside the mother

s
uterus if specialized medical care
is available


Before 22 weeks… Brain is not
developed enough to control the
organs and bodily functions




41

From Viability to Full Term


Difference between preterm and newborn is the maturation
of neurological, respiratory, cardiovascular systems

42


Born at just under 22 weeks gestation,
Amillia

is the world's youngest surviving
premature baby.


She was just 9 1/2 inches at birth and
weighed less than 10 ounces


She will still require oxygen at home and a
developmental specialist will follow up with
her to track her neurological development


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Maternal Factors


Teratogenic: birth defect producing


Nutrition and maternal weight


Drug and alcohol intake


Nicotine


Caffeine


Maternal illnesses


Sexually transmitted diseases (HIV/AIDS)


Maternal age and stress


Outside environmental hazards


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Paternal Factors


May affect quality of sperm:


Exposure to lead


Marijuana or tobacco smoke


Alcohol or radiation


Pesticides


Paternal age

Teratogens produce specific
abnormalities at specific times


Conception until implantation


Do not cause non
-
genetic congenital malformations unless
the agent persists in the body beyond this period


Embryonic period


Period of maximum sensitivity to teratogens


Exposure to
teratogenic

agents during this period has the
greatest likelihood of causing a
structural

anomaly


Fetal phase


Teratogen exposure affects
size

or
function

of an organ.

45

Genetic Vulnerability


46

Smoking: Pregnancy
complications


Adverse effects of smoking in pregnancy are due mainly to
smoking in the second and third trimesters


Cigarettes can impede the flow of blood in the placenta which
in turn restricts the amount of nutrients that reach the fetus.


Cigarette smoking has been linked to


Spontaneous abortion (miscarriage)


Substantially higher in women who smoke


Premature birth


Low birth weight


Sudden Infant Death Syndrome


Inadequate breast milk production and nutrients in the milk


47


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Monitoring Prenatal Development


Ultrasound and amniocentesis


Chorionic villus sampling CVS)


Embryoscopy


Maternal blood test


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Prenatal Care


Includes:


Education


Social services


Nutritional services



Helps protect the life and health of the
infant and mother


Not evenly distributed among SES, ethnic
groups


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Preconception care


CDC recommendations include:


Physical examinations


Vaccinations


Risk screening


Counseling