Why are recessive disorders more common than dominant ones?

Agenda1.Genetic disorders2.Pedigrees

What are the chances of 2 carriers of cystic fibrosis will have a child with CF?• The odds of one carrier (1/23.6) marrying

another carrier (1/23.6) is 1/500

• The occurrence of CF is about 1/2000

How can we see the prevalence of a trait in a family over a long period of

time?Agenda1.Genetic Disorder Notes2.Pedigrees

Nondisjunction

• Cell division chromosomes separate– Nondisjunction occurs when chromosomes fail to

separate

• More chromosomes than usual– Trisomy – set of three chromosomes of one kind– Monosomy – set of 1 chromosome

Nondisjunction• Down Syndrome

Pedigrees

• Pedigree – diagram that traces the inheritance of a particular trait through several generations

Pedigrees

Symbols

Analyzing Pedigrees

Inferring Genotypes

• Use pedigrees to infer genotypes– Determine genotype from phenotype– Dominant traits are easier to identify

• dominant traits are exhibited in the phenotype

• If good records have been kept you can predict disorders in future offspring

Polydactyl – Dominant Disorder

Questions• Is this trait dominant or recessive? Explain your

answer.• Name the 2 individuals that were carriers of

hemophilia• How are individuals III-1 and III-2 related? • How many children did individuals I-1 and I-2

have• How many girls did II-1 and II-2 have? How many

have hemophilia?

Is this a recessive or dominant trait?How are person II2 and II3 related?Agenda1.Pedigree Review2.Pedigree Practice3.Movie

The pedigree to the right shows a family’s pedigree for colorblindness (a sex linked trait)

Which sex can be carriers of colorblindness and not have it?Why does individual IV-7 have colorblindness?  Why do all the daughters in generation II carry the colorblind

gene? IV

Agenda1.Finish yesterday’s movie2.Lorenzo’s oil