genetic testing and counseling genetic counselors can provide information to prospective parents...
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Genetic Testing and Counseling
• Genetic counselors can provide information to prospective parents concerned about a family history for a specific disease
© 2011 Pearson Education, Inc.
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Counseling Based on Mendelian Genetics and Probability Rules
• Using family histories, genetic counselors help couples determine the odds that their children will have genetic disorders
• Probabilities are predicted on the most accurate information at the time; predicted probabilities may change as new information is available
© 2011 Pearson Education, Inc.
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Tests for Identifying Carriers
• For a growing number of diseases, tests are available that identify carriers and help define the odds more accurately
© 2011 Pearson Education, Inc.
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Figure 14.18
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Fetal Testing
• In amniocentesis, the liquid that bathes the fetus is removed and tested
• In chorionic villus sampling (CVS), a sample of the placenta is removed and tested
• Other techniques, such as ultrasound and fetoscopy, allow fetal health to be assessed visually in utero
© 2011 Pearson Education, Inc.
Video: Ultrasound of Human Fetus I
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Figure 14.19
(a) Amniocentesis (b) Chorionic villus sampling (CVS)
Ultrasound monitor
Amnioticfluidwithdrawn
FetusPlacentaUterus Cervix
Centrifugation
Fluid
Fetal cells
Several hours
Severalweeks
Several weeks
Biochemicaland genetic
tests
Karyotyping
Ultrasoundmonitor
Fetus
Placenta
Chorionic villi
Uterus
Cervix
Suctiontubeinsertedthroughcervix
Several hours
Fetal cells
Several hours
1
1
2
2
3
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Newborn Screening
• Some genetic disorders can be detected at birth by simple tests that are now routinely performed in most hospitals in the United States
© 2011 Pearson Education, Inc.
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Figure 14.UN03
Complete dominanceof one allele
Relationship amongalleles of a single gene
Description Example
Incomplete dominanceof either allele
Codominance
Multiple alleles
Pleiotropy
Heterozygous phenotypesame as that of homo-zygous dominant
Heterozygous phenotypeintermediate betweenthe two homozygousphenotypes
Both phenotypesexpressed inheterozygotes
In the whole population,some genes have morethan two alleles
One gene is able to affectmultiple phenotypiccharacters
ABO blood group alleles
Sickle-cell disease
PP Pp
CRCR CRCW CWCW
IAIB
IA, IB, i
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Figure 14.UN04
Epistasis
Polygenic inheritance
Relationship amongtwo or more genes Description Example
The phenotypicexpression of onegene affects thatof another
A single phenotypiccharacter is affectedby two or more genes
9 : 3 : 4
BbEe BbEe
BEBE
bE
bE
Be
Be
be
be
AaBbCc AaBbCc
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Figure 14.UN05
Flower position
Stem length
Seed shape
Character Dominant Recessive
Axial (A)
Tall (T)
Round (R)
Terminal (a)
Dwarf (t)
Wrinkled (r)
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Figure 14.UN07
George Arlene
Sandra Tom Sam Wilma Ann Michael
Carla
Daniel Alan Tina
Christopher
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Figure 14.UN06
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Figure 14.UN08
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Figure 14.UN09
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Figure 14.UN10
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Figure 14.UN14