5 & 6 Problem Solving

the proportion of times a specific outcome occurs in a series of events

eg. in a pregnancy: 1/2 girl, 1/2 boy

the outcome of one event does NOT depend on outcome of other event

eg. a previous pregnancy does NOT affect a future one

each conception: 1/2 boys, 1/2 girls

if 2 events are INDEPENDENT of each other, the probability of outcome of both occurrences happening is the product of each outcome

eg. the chance of having 3 children & all of them be girls = 1/2 * 1/2 * 1/2 = 1/8

• the probability of one outcome OR another is the addition of each outcome
• boy or girl = 1/2 + 1/2 = 1

• • probability of getting EITHER 2 heads in a row OR 2 tails in a row =
• (1/2 * 1/2) + (1/2 * 1/2) = 1/4 + 1/4 = 1

frequency of the dominant ALLELE in a population (present in people with both AA & Aa)

frequency of the recessive ALLELE in a population (present in people with both Aa & aa)

1

how many people have the aa genotype

• the incidence of homozygous recessive people in a population

• eg. CF (AR) has an incidence of 1/2500
• - that means 1 in every 2500 people HAS CF, so q² = 1/2500

how many people have the Aa genotype

• the incidence of heterozygous people in a population

• what you’re looking for if someone asks you what a CARRIER RATE is

how many people have the AA genotype

• the incidence of homozygous dominant people in a population

multiply each of their chances

eg. for 2 siblings: 1/4 * 1/4 = 1/16 chance that all are affected

multiply each of their chances

eg. for 2 siblings: 3/4 * 3/4 = 9/16 chance that none of them are affected

1 — NONE

eg. from above example, 1 - 9/16 = 7/16 chance at least 1 child will be AFFECTED

• eg. if Penetrance = 60%, then there’s a 60% chance each affected individual expresses the trait

~ 0.5%

• if a child’s risk for being affected by a condition is LOWER than the risk of Amniocentesis, it’s NOT offered