Download Why are recessive disorders more common than dominant ones?

Why are recessive disorders more
common than dominant ones?
Agenda
1. Genetic disorders
2. 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?
Agenda
1. Genetic Disorder Notes
2. 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?
Agenda
1. Pedigree Review
2. Pedigree Practice
3. 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
Agenda
1.Finish
yesterday’s
movie
2.Lorenzo’s oil