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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)