chapter 3 - heredity

multiplication rule

apply when two events occur simultaneously

addition rule

apply when two events are mutually exclusive

shortest path

apply when there are many “paths” to giving a probability

conditional probability

occurs when we must apply a specific condition to a probability

In a pile of cards with six equally possible colors (red, blue, green, black, yellow, orange), what is the probability of drawing a red card?

1/6 chance

P(Red and Blue)

1/6 ×1/6 = 1/36

multiplication rule

P(Red or Blue) = P(Red) + P(Blue)

1/6 + 1/6 = 2/6 = 1/3

P(Not Red) = 1 - P(Red)

1 - 1/6 = 6/6 - 1/6 = 5/6

P(Red, then Blue, then Orange)

1/6 × 1/6 × 1/6 = 1/216

cystic fibrosis

caused by an autosomal recessive allele, leading to thick mucus buildup that affects multiple organ systems

genotype ratio

For two heterozygous pairs: 1:2:1 for both A and B.

Possible combinations of alleles (AA, Aa, aa with BB, Bb, bb) give 9 unique genotypes.

phenotype ratio

For a dihybrid cross with complete dominance: typical phenotype ratio: 9:3:3:1

method 1 - dihybrid punnett square

Create a 4x4 grid to represent all combinations for AaBb x AaBb

Resulting genotype ratio: 9 unique combinations

method 2 - multiplication rule

For independent traits, multiply individual trait probabilities: P(Aa) = 1/2, P(Bb) = 1/2

To get the probability of a specific combination, multiply these probabilities together.

method 3 - forked-line method

Use a forked-line diagram to separate the two traits (A and B).

Follow the possible combinations for each trait and multiply the probabilities for independent inheritance.

forked-line method

forked-line diagram method simplifies complex genetic crosses by visualizing the probabilities of each trait separately