Human Genetic Disorders

Harmful or Beneficial?

Human Genetic Disorders

• Mutations are key– DNA change change in alleles

• Chromosomal errors – nondisjunction

– Deletion, inversion, translocation

Disorders may be…

• In germ cells or somatic cells

• Dominant or recessive

• Autosomes or Sex linked

• Most such disorders are caused by autosomal recessive alleles– Examples:

cystic fibrosis, sickle-cell disease

Many inherited disorders in humans are controlled by a single gene

Figure 9.9A

D D

d d

NormalDd

NormalDd

DDNormal

DdNormal(carrier)

DdNormal(carrier)

ddDeaf

Eggs Sperm

PARENTS

OFFSPRING

• A few are caused by dominant alleles

Figure 9.9B

– Examples: achondroplasia, Huntington’s disease

Table 9.9

Tracking Traits & Prediction

• Before mating– Genetic screening - karyotype

– Punnets

– Pedigree analysis

• Family pedigrees are used to determine patterns of inheritance and individual genotypes

Figure 9.8B

DdJoshuaLambert

DdAbigailLinnell

D_Abigail

Lambert

Female

DdElizabeth

Eddy

D_JohnEddy

? D_HepzibahDaggett

?

?

ddDdDdDdddDdDd

MaleDeaf

Hearing

ddJonathanLambert

• Fetal cells can be obtained through amniocentesis

Genetic testing

Figure 9.10A

Amnioticfluid

Fetus(14-20weeks)

Placenta

Amnioticfluidwithdrawn

Centrifugation

Fetalcells

Fluid

Uterus Cervix Cell culture

Severalweeks later Karyotyping

Biochemicaltests

After fertilization• Amniocentesis• Chorionic villi sampling• Protein tests/biochemical tests via urine

samples• Ultrasound (sonogram)

• **Genetic counseling for all**

• Chorionic villus sampling obtains fetal cells for karyotyping

Figure 9.10B

Fetus(10-12weeks)

Placenta

Chorionic villi

Suction

Several hourslater

Fetal cells(from chorionic villi)

Karyotyping

Some biochemical

tests

• Uultrasound (sonogram)

Figure 9.10C, D

Risks to consider:

• Harm to baby– Invasive, risk of miscarriage

• Harm to mother– Invasive, risk of infection

• Ethical, moral, personal decisions