Objective: What is the purpose of a test-cross in genetics?

Do Now:

Black hair: B

Blonde hair: b

What would the gene combination look like for someone who is homozygous dominant for the trait?

Genotype

Genotype: the genetic makeup of an organism, or the combination of alleles (ex: BB)

Phenotype

Phenotype: Physical appearance of an organism, an observable trait (ex: black hair)

Punnett Square- A genetic cross that shows all

possible outcomes of offspring

Test Cross

- Breeds an individual of unknown genotype, but dominant phenotype with a homozygous recessive individual

- Ex: Are you Bb or BB? Perform a test cross with a bb to determine the possibilities!

Lets say you have Black hair…do you know your genotype? How could we figure out what your genotype is?

Law of Segregation

Law of Independent Assortment

• Law of segregation: When a parent forms sex cells (egg or sperm), the parent’s gene pairs separate, so the sex cells carry only 1 allele for a particular trait

• Law of independent assortment: gene pairs are inherited independently of the gene pairs for all other traits.

• Law of Dominance: Only need to inherit 1 dominant allele to show trait

Dihybrid CrossA cross between organisms that

differ in TWO characteristics (seed shape and seed color in pea plants)