Pedigrees & Human Diseases

Additional Topics in Genetics

Bio 391

PEDIGREES another way to study inheritance

How to read a pedigree…

Carrier female

Carrier male

• What do you think the F1 generation (line II) # 2 and #5 offspring represent?

• Can you draw the Punnett Square for the Parent generation? (I)

Pedigrees• Helpful because human breeding experiments

are difficult• Show how traits are passed down through many

generations• Based mostly on phenotypes; after the fact• Show the actual offspring

– Punnett squares show the possible offspring

• Really only works well for single traits– Not polygenic traits

• Only works for inherited traits– Environmental factors play a large role in who we are

Inheriting Diseases

• Just like physical traits, some diseases can be inherited on our chromosomes.

• And, just like physical traits, some are X-linked, some are recessive, some are dominant or codominant.

• Are you predisposed??

Human Genetic Disorders• When a genetic disorder is autosomal

dominant, an individual with AA or Aa has the disorder.– Autosomal dominant disorders are rarely lethal– When a genetic disorder is autosomal recessive,

only aa individuals have the disorder.– Recall carriers are usually healthy

Most children with recessive disorders are born to parents with a normal phenotype (carriers).

• A key to assessing risk –identify carrier status• Recently developed tests for several disorders can

distinguish between normal phenotypes in heterozygotes from homozygous dominants.

• The results allow individuals with a family history of a genetic disorder to make informed decisions about having children.

• However, issues of confidentiality, discrimination, and adequate information and counseling arise.

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Prenatal Testing:

• Amniocentesis – sample of fluid surrounding fetus, contains some fetal cells –

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 14.17a

In utero testing to determine if a child will have a disorder

• Chorionic villus sampling (CVS)– Pieces of tissue (chorion connecting mother

and fetus) are removed

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 14.17b

Ethical Dilemma

• You are an employer and have 2 equally qualified candidates for a job. According to human resources, one of the candidates will develop Huntington disease and will likely be unable to work for longer than 10 years. What do you do?

• GINA – Genetic Information Nondiscrimination Act of 2008

Genetic DisordersGaucher disease

Duschene Muscular Dystrophy

Marfan syndromeColor blindnessHurler syndrome

HemophiliaLesch-Nyhan disease

SCIDSProgeria

AchondroplasiaEdwards SyndromeBloom’s syndrome

Prader-Willi SyndromeWilson’s disease

Fragile X syndromeTay-SachsAlbinism

Cystic FibrosisSickle cell anemia

PKULou Gehrig’s diseaseCri du Chat syndromeHuntington DiseaseTurner’s syndrome

Klinefelter syndromeDown syndromeFanconi anemia