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.

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.

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.

Figure 14.18

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

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

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.

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

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

Figure 14.UN05

Flower position

Stem length

Seed shape

Character Dominant Recessive

Axial (A)

Tall (T)

Round (R)

Terminal (a)

Dwarf (t)

Wrinkled (r)

Figure 14.UN07

George Arlene

Sandra Tom Sam Wilma Ann Michael

Carla

Daniel Alan Tina

Christopher

Figure 14.UN06

Figure 14.UN08

Figure 14.UN09

Figure 14.UN10

Figure 14.UN11

Figure 14.UN12

Figure 14.UN13

Figure 14.UN14