LESSON 1: Dihybrid crosses: The Principle of Independent Assortment

haploid gametes

produced by a plant contain one copy of each gene.

THE PUNNETT SQUARE METHOD

- Used when showing the cross between one or two genes.

- Gametes are write down and combine them systematically to generate the array of zygotic phenotypes.

G

= yellow (dominant) Dihybrid cross

g

= green (recessive) Dihybrid cross

W

= round (dominant) Dihybrid cross

w

= wrinkle (recessive) Dihybrid cross

Phenylketonuria (PKU)

- caused by a recessive allele that doesn't code for the enzyme that breaks down the amino acid phenylalanine.

- This disease can result in mental retardation or death.

- "E"

"E"

represent the normal enzyme.

"G"

- represent the normal allele for galactose digestion.

- = normal for galactose digestion

g

= galactose intolerance

THE FORKED-LINE METHOD

- Another procedure for predicting the outcome of a cross involving two or more genes.

- Tallying the gametes in a diagram of branching lines.