Lecture 7 Population Genetics

Bayes’s Theorem Prenatal Screening

Mother is 20 years old= 1/1500 risk

Fetus is positive for nuchal translucency

5% of healthy fetuses are positive

75% of affected fetuses are positive

/(P(does not have down syndrome +P(does have down syndrome)

Q1. what is the risk that III2 is a carrier for Duchenne muscular dystrophy (DMD)

X linked recessive

We can assume that other females are carrier

Serum creative kinase is normal (indicator of subclinical muscle damage common in DMD carriers)

2/3 carriers have abnormal results

1/3 of carriers have normal results

All healthy people have normal results

A. ¼

Describe Retinoblastoma? How is it inherited?

Hereditary retinoblastoma (Rb), which is a
cancer of the retina occurring before the age
of 5
²Autosomal Dominant

The risk that II1 has the genotype without the phenotype is 1/6

What are the odds that III1 has the mutated allele

The reason we don’t do bayes is because they are independent events

8/9

Q3 Estimating carrier incidence

A disease is inherited as AR

Disease incidence is 1/1600 in population X

What are the odds that a random person from pop X is a carrier?