5 2 Studying Genetic Crosses SBI 3 U

5. 2 - Studying Genetic Crosses SBI 3 U 1 - Ferrari

Punnett Squares • Punnett Square- A grid used to illustrate all possible genotypes and phenotypes of offspring from genetic crosses • Shows probability • Each square represents a 25% chance of occurrence for that trait

Using Punnett Squares This is a monohybrid cross Possible F 1 outcomes from a cross between two heterozygous parents. The phenotype ratio is 3: 1 for flower colour (purple to white)

Test Crosses A cross between an individual of unknown genotype and homozygous recessive for that trait. Analyzing the phenotype should provide insight into the unknown genotype.

Mendel’s Dihybrid Crosses He crossed yellow, round seeds with green, wrinkled seeds YYRR x yyrr All F 1 generation displayed both dominant traits- yellow and round

The Law of Independent Assortment • Mendel found a 9: 3: 3: 1 ratio for every dihybrid cross he performed. • This law states that the alleles for one gene segregate or assort independently of the alleles for other genes during gamete formation.

The Chromosome Theory of Inheritance By early 1900 s scientists finally began to see the link between meiosis & inheritance Walter Sutton ( 1902) proposed that genes located on chromosomes and this provides the basis for the segregation and independent assortment of alleles.

Homework • 1) Please read and review 5. 2 ( Pgs. 208 -217) • 2) Punnett Square Practice Problems & Worksheets